Docker Intensif

Docker Intensif

```

These slides have been built from commit: af86f36

[shared/title.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/shared/title.md)]
---

Docker Intensif

.footnote[
**Slides[:](https://www.youtube.com/watch?v=h16zyxiwDLY) https://2022-02-enix.container.training/**
]

<!--
WiFi: **Something** 
Password: **Something**

**Be kind to the WiFi!** 
*Use the 5G network.*
*Don't use your hotspot.* 
*Don't stream videos or download big files during the workshop* 
*Thank you!*
-->

.debug[[shared/title.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/shared/title.md)]
---
## Introductions

- Hello!

- On stage: Jérôme ([@jpetazzo])

- Backstage: Alexandre, Amy, Antoine, Aurélien (x2), Benji, David, Julien, Kostas, Nicolas, Thibault

- The training will run from 9:30 to 13:00

- There will be a break at (approximately) 11:00

- You ~~should~~ must ask questions! Lots of questions!

- Use [Mattermost](https://highfive.container.training/mattermost) to ask questions, get help, etc.

[@alexbuisine]: https://twitter.com/alexbuisine
[EphemeraSearch]: https://ephemerasearch.com/
[@jpetazzo]: https://twitter.com/jpetazzo
[@s0ulshake]: https://twitter.com/s0ulshake
[Quantgene]: https://www.quantgene.com/

.debug[[logistics.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/logistics.md)]
---

## Exercises

- At the end of each day, there is a series of exercises

- To make the most out of the training, please try the exercises!

(it will help to practice and memorize the content of the day)

- We recommend to take at least one hour to work on the exercises

(if you understood the content of the day, it will be much faster)

- Each day will start with a quick review of the exercises of the previous day

.debug[[logistics.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/logistics.md)]
---
## A brief introduction

- This was initially written to support in-person, instructor-led workshops and tutorials

- These materials are maintained by [Jérôme Petazzoni](https://twitter.com/jpetazzo) and [multiple contributors](https://github.com/jpetazzo/container.training/graphs/contributors)

- You can also follow along on your own, at your own pace

- We included as much information as possible in these slides

- We recommend having a mentor to help you ...

- ... Or be comfortable spending some time reading the Docker
 [documentation](https://docs.docker.com/) ...

- ... And looking for answers in the [Docker forums](forums.docker.com),
  [StackOverflow](http://stackoverflow.com/questions/tagged/docker),
  and other outlets

.debug[[containers/intro.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/intro.md)]
---

## Hands on, you shall practice

- Nobody ever became a Jedi by spending their lives reading Wookiepedia

- Likewise, it will take more than merely *reading* these slides
  to make you an expert

- These slides include *tons* of demos, exercises, and examples

- They assume that you have access to a machine running Docker

- If you are attending a workshop or tutorial:
 you will be given specific instructions to access a cloud VM

- If you are doing this on your own:
 we will tell you how to install Docker or access a Docker environment

.debug[[containers/intro.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/intro.md)]
---
## Accessing these slides now

- We recommend that you open these slides in your browser:

https://2022-02-enix.container.training/

- Use arrows to move to next/previous slide

(up, down, left, right, page up, page down)

- Type a slide number + ENTER to go to that slide

- The slide number is also visible in the URL bar

(e.g. .../#123 for slide 123)

.debug[[shared/about-slides.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/shared/about-slides.md)]
---

## Accessing these slides later

- Slides will remain online so you can review them later if needed

(let's say we'll keep them online at least 1 year, how about that?)

- You can download the slides using that URL:

https://2022-02-enix.container.training/slides.zip

(then open the file `1.yml.html`)

- You will find new versions of these slides on:

https://container.training/

.debug[[shared/about-slides.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/shared/about-slides.md)]
---

## These slides are open source

- You are welcome to use, re-use, share these slides

- These slides are written in Markdown

- The sources of these slides are available in a public GitHub repository:

https://github.com/jpetazzo/container.training

- Typos? Mistakes? Questions? Feel free to hover over the bottom of the slide ...

.footnote[👇 Try it! The source file will be shown and you can view it on GitHub and fork and edit it.]

.debug[[shared/about-slides.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/shared/about-slides.md)]
---

## Extra details

- This slide has a little magnifying glass in the top left corner

- This magnifying glass indicates slides that provide extra details

- Feel free to skip them if:

- you are in a hurry

- you are new to this and want to avoid cognitive overload

- you want only the most essential information

- You can review these slides another time if you want, they'll be waiting for you ☺

.debug[[shared/about-slides.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/shared/about-slides.md)]
---
## Chat room

- We've set up a chat room that we will monitor during the workshop

- Don't hesitate to use it to ask questions, or get help, or share feedback

- The chat room will also be available after the workshop

- Join the chat room: [Mattermost](https://highfive.container.training/mattermost)

- Say hi in the chat room!

.debug[[shared/chat-room-im.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/shared/chat-room-im.md)]
---

## Part 1

- [Our training environment](#toc-our-training-environment)

- [Our first containers](#toc-our-first-containers)

- [Background containers](#toc-background-containers)

- [Understanding Docker images](#toc-understanding-docker-images)

- [Building images interactively](#toc-building-images-interactively)

- [Building Docker images with a Dockerfile](#toc-building-docker-images-with-a-dockerfile)

- [`CMD` and `ENTRYPOINT`](#toc-cmd-and-entrypoint)

- [Copying files during the build](#toc-copying-files-during-the-build)

- [Exercise — writing Dockerfiles](#toc-exercise--writing-dockerfiles)

## Part 2

- [Container networking basics](#toc-container-networking-basics)

- [Local development workflow with Docker](#toc-local-development-workflow-with-docker)

- [The Container Network Model](#toc-the-container-network-model)

- [Service discovery with containers](#toc-service-discovery-with-containers)

- [Compose for development stacks](#toc-compose-for-development-stacks)

- [Exercise — writing a Compose file](#toc-exercise--writing-a-compose-file)

## Part 3

- [Restarting and attaching to containers](#toc-restarting-and-attaching-to-containers)
- [Naming and inspecting containers](#toc-naming-and-inspecting-containers)
- [Labels](#toc-labels)
- [Getting inside a container](#toc-getting-inside-a-container)
- [Tips for efficient Dockerfiles](#toc-tips-for-efficient-dockerfiles)
- [Dockerfile examples](#toc-dockerfile-examples)
- [Advanced Dockerfile Syntax](#toc-advanced-dockerfile-syntax)
- [Reducing image size](#toc-reducing-image-size)
- [Multi-stage builds](#toc-multi-stage-builds)
- [Publishing images to the Docker Hub](#toc-publishing-images-to-the-docker-hub)
- [Exercise — writing better Dockerfiles](#toc-exercise--writing-better-dockerfiles)

## Part 4

- [Buildkit](#toc-buildkit)

- [Container network drivers](#toc-container-network-drivers)

- [Deep dive into container internals](#toc-deep-dive-into-container-internals)

- [Control groups](#toc-control-groups)

- [Namespaces](#toc-namespaces)

- [Security features](#toc-security-features)

- [Orchestration, an overview](#toc-orchestration-an-overview)

.debug[[shared/toc.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/shared/toc.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/Container-Ship-Freighter-Navigation-Elbe-Romance-1782991.jpg)]

---

Our training environment

.nav[
[Previous part](#toc-)
|
[Back to table of contents](#toc-part-1)
|
[Next part](#toc-our-first-containers)
]

---

# Our training environment

![SSH terminal](images/title-our-training-environment.jpg)

.debug[[containers/Training_Environment.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Training_Environment.md)]
---

## Our training environment

- If you are attending a tutorial or workshop:

- a VM has been provisioned for each student

- If you are doing or re-doing this course on your own, you can:

- install Docker locally (as explained in the chapter "Installing Docker")

- install Docker on e.g. a cloud VM

- use https://www.play-with-docker.com/ to instantly get a training environment

.debug[[containers/Training_Environment.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Training_Environment.md)]
---

## Our Docker VM

*This section assumes that you are following this course as part of
a tutorial, training or workshop, where each student is given an
individual Docker VM.*

- The VM is created just before the training.

- It will stay up during the whole training.

- It will be destroyed shortly after the training.

- It comes pre-loaded with Docker and some other useful tools.

.debug[[containers/Training_Environment.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Training_Environment.md)]
---

## What *is* Docker?

- "Installing Docker" really means "Installing the Docker Engine and CLI".

- The Docker Engine is a daemon (a service running in the background).

- This daemon manages containers, the same way that a hypervisor manages VMs.

- We interact with the Docker Engine by using the Docker CLI.

- The Docker CLI and the Docker Engine communicate through an API.

- There are many other programs and client libraries which use that API.

.debug[[containers/Training_Environment.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Training_Environment.md)]
---

## Why don't we run Docker locally?

- We are going to download container images and distribution packages.

- This could put a bit of stress on the local WiFi and slow us down.

- Instead, we use a remote VM that has a good connectivity

- In some rare cases, installing Docker locally is challenging:

- no administrator/root access (computer managed by strict corp IT)

- 32-bit CPU or OS

- old OS version (e.g. CentOS 6, OSX pre-Yosemite, Windows 7)

- It's better to spend time learning containers than fiddling with the installer!

.debug[[containers/Training_Environment.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Training_Environment.md)]
---

## Connecting to your Virtual Machine

You need an SSH client.

* On OS X, Linux, and other UNIX systems, just use `ssh`:

```bash
$ ssh <login>@<ip-address>
```

* On Windows, if you don't have an SSH client, you can download:

* Putty (www.putty.org)

* Git BASH (https://git-for-windows.github.io/)

* MobaXterm (https://mobaxterm.mobatek.net/)

.debug[[containers/Training_Environment.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Training_Environment.md)]
---

## `tailhist`

The shell history of the instructor is available online in real time.

Note the IP address of the instructor's virtual machine (A.B.C.D).

Open http://A.B.C.D:1088 in your browser and you should see the history.

The history is updated in real time (using a WebSocket connection).

It should be green when the WebSocket is connected.

If it turns red, reloading the page should fix it.

.debug[[containers/Training_Environment.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Training_Environment.md)]
---

## Checking your Virtual Machine

Once logged in, make sure that you can run a basic Docker command:

.small[
```bash
$ docker version
Client:
 Version:       18.03.0-ce
 API version:   1.37
 Go version:    go1.9.4
 Git commit:    0520e24
 Built:         Wed Mar 21 23:10:06 2018
 OS/Arch:       linux/amd64
 Experimental:  false
 Orchestrator:  swarm

Server:
 Engine:
  Version:      18.03.0-ce
  API version:  1.37 (minimum version 1.12)
  Go version:   go1.9.4
  Git commit:   0520e24
  Built:        Wed Mar 21 23:08:35 2018
  OS/Arch:      linux/amd64
  Experimental: false
```
]

If this doesn't work, raise your hand so that an instructor can assist you!

???

:EN:Container concepts
:FR:Premier contact avec les conteneurs

:EN:- What's a container engine?
:FR:- Qu'est-ce qu'un *container engine* ?

.debug[[containers/Training_Environment.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Training_Environment.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/ShippingContainerSFBay.jpg)]

---

Our first containers

.nav[
[Previous part](#toc-our-training-environment)
|
[Back to table of contents](#toc-part-1)
|
[Next part](#toc-background-containers)
]

---

# Our first containers

![Colorful plastic tubs](images/title-our-first-containers.jpg)

.debug[[containers/First_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/First_Containers.md)]
---

## Objectives

At the end of this lesson, you will have:

* Seen Docker in action.

* Started your first containers.

.debug[[containers/First_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/First_Containers.md)]
---

## Hello World

In your Docker environment, just run the following command:

```bash
$ docker run busybox echo hello world
hello world
```

(If your Docker install is brand new, you will also see a few extra lines,
corresponding to the download of the `busybox` image.)

.debug[[containers/First_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/First_Containers.md)]
---

## That was our first container!

* We used one of the smallest, simplest images available: `busybox`.

* `busybox` is typically used in embedded systems (phones, routers...)

* We ran a single process and echo'ed `hello world`.

.debug[[containers/First_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/First_Containers.md)]
---

## A more useful container

Let's run a more exciting container:

```bash
$ docker run -it ubuntu
root@04c0bb0a6c07:/#
```

* This is a brand new container.

* It runs a bare-bones, no-frills `ubuntu` system.

* `-it` is shorthand for `-i -t`.

* `-i` tells Docker to connect us to the container's stdin.

* `-t` tells Docker that we want a pseudo-terminal.

.debug[[containers/First_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/First_Containers.md)]
---

## Do something in our container

Try to run `figlet` in our container.

```bash
root@04c0bb0a6c07:/# figlet hello
bash: figlet: command not found
```

Alright, we need to install it.

.debug[[containers/First_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/First_Containers.md)]
---

## Install a package in our container

We want `figlet`, so let's install it:

```bash
root@04c0bb0a6c07:/# apt-get update
...
Fetched 1514 kB in 14s (103 kB/s)
Reading package lists... Done
root@04c0bb0a6c07:/# apt-get install figlet
Reading package lists... Done
...
```

One minute later, `figlet` is installed!

.debug[[containers/First_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/First_Containers.md)]
---

## Try to run our freshly installed program

The `figlet` program takes a message as parameter.

```bash
root@04c0bb0a6c07:/# figlet hello
 _          _ _       
| |__   ___| | | ___  
| '_ \ / _ \ | |/ _ \ 
| | | |  __/ | | (_) |
|_| |_|\___|_|_|\___/ 
```

Beautiful! 😍

.debug[[containers/First_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/First_Containers.md)]
---

## Counting packages in the container

Let's check how many packages are installed there.

```bash
root@04c0bb0a6c07:/# dpkg -l | wc -l
97
```

* `dpkg -l` lists the packages installed in our container

* `wc -l` counts them

How many packages do we have on our host?

.debug[[containers/First_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/First_Containers.md)]
---

## Counting packages on the host

Exit the container by logging out of the shell, like you would usually do.

(E.g. with `^D` or `exit`)

```bash
root@04c0bb0a6c07:/# exit
```

Now, try to:

* run `dpkg -l | wc -l`. How many packages are installed?

* run `figlet`. Does that work?

.debug[[containers/First_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/First_Containers.md)]
---

## Comparing the container and the host

Exit the container by logging out of the shell, with `^D` or `exit`.

Now try to run `figlet`. Does that work?

(It shouldn't; except if, by coincidence, you are running on a machine where figlet was installed before.)

.debug[[containers/First_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/First_Containers.md)]
---

## Host and containers are independent things

* We ran an `ubuntu` container on an Linux/Windows/macOS host.

* They have different, independent packages.

* Installing something on the host doesn't expose it to the container.

* And vice-versa.

* Even if both the host and the container have the same Linux distro!

* We can run *any container* on *any host*.

(One exception: Windows containers can only run on Windows hosts; at least for now.)

.debug[[containers/First_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/First_Containers.md)]
---

## Where's our container?

* Our container is now in a *stopped* state.

* It still exists on disk, but all compute resources have been freed up.

* We will see later how to get back to that container.

.debug[[containers/First_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/First_Containers.md)]
---

## Starting another container

What if we start a new container, and try to run `figlet` again?
 
```bash
$ docker run -it ubuntu
root@b13c164401fb:/# figlet
bash: figlet: command not found
```

* We started a *brand new container*.

* The basic Ubuntu image was used, and `figlet` is not here.

.debug[[containers/First_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/First_Containers.md)]
---

## Where's my container?

* Can we reuse that container that we took time to customize?

*We can, but that's not the default workflow with Docker.*

* What's the default workflow, then?

*Always start with a fresh container.*
 
 *If we need something installed in our container, build a custom image.*

* That seems complicated!

*We'll see that it's actually pretty easy!*

* And what's the point?

*This puts a strong emphasis on automation and repeatability. Let's see why ...*

.debug[[containers/First_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/First_Containers.md)]
---

## Pets vs. Cattle

* In the "pets vs. cattle" metaphor, there are two kinds of servers.

* Pets:

* have distinctive names and unique configurations

* when they have an outage, we do everything we can to fix them

* Cattle:

* have generic names (e.g. with numbers) and generic configuration

* configuration is enforced by configuration management, golden images ...

* when they have an outage, we can replace them immediately with a new server

* What's the connection with Docker and containers?

.debug[[containers/First_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/First_Containers.md)]
---

## Local development environments

* When we use local VMs (with e.g. VirtualBox or VMware), our workflow looks like this:

* create VM from base template (Ubuntu, CentOS...)

* install packages, set up environment

* work on project

* when done, shut down VM

* next time we need to work on project, restart VM as we left it

* if we need to tweak the environment, we do it live

* Over time, the VM configuration evolves, diverges.

* We don't have a clean, reliable, deterministic way to provision that environment.

.debug[[containers/First_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/First_Containers.md)]
---

## Local development with Docker

* With Docker, the workflow looks like this:

* create container image with our dev environment

* run container with that image

* work on project

* when done, shut down container

* next time we need to work on project, start a new container

* if we need to tweak the environment, we create a new image

* We have a clear definition of our environment, and can share it reliably with others.

* Let's see in the next chapters how to bake a custom image with `figlet`!

???

:EN:- Running our first container
:FR:- Lancer nos premiers conteneurs

.debug[[containers/First_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/First_Containers.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/aerial-view-of-containers.jpg)]

---

Background containers

.nav[
[Previous part](#toc-our-first-containers)
|
[Back to table of contents](#toc-part-1)
|
[Next part](#toc-understanding-docker-images)
]

---

# Background containers

![Background containers](images/title-background-containers.jpg)

.debug[[containers/Background_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Background_Containers.md)]
---

## Objectives

Our first containers were *interactive*.

We will now see how to:

* Run a non-interactive container.
* Run a container in the background.
* List running containers.
* Check the logs of a container.
* Stop a container.
* List stopped containers.

.debug[[containers/Background_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Background_Containers.md)]
---

## A non-interactive container

We will run a small custom container.

This container just displays the time every second.

```bash
$ docker run jpetazzo/clock
Fri Feb 20 00:28:53 UTC 2015
Fri Feb 20 00:28:54 UTC 2015
Fri Feb 20 00:28:55 UTC 2015
...
```

* This container will run forever.
* To stop it, press `^C`.
* Docker has automatically downloaded the image `jpetazzo/clock`.
* This image is a user image, created by `jpetazzo`.
* We will hear more about user images (and other types of images) later.

.debug[[containers/Background_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Background_Containers.md)]
---

## When `^C` doesn't work...

Sometimes, `^C` won't be enough.

Why? And how can we stop the container in that case?

.debug[[containers/Background_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Background_Containers.md)]
---

## What happens when we hit `^C`

`SIGINT` gets sent to the container, which means:

- `SIGINT` gets sent to PID 1 (default case)

- `SIGINT` gets sent to *foreground processes* when running with `-ti`

But there is a special case for PID 1: it ignores all signals!

- except `SIGKILL` and `SIGSTOP`

- except signals handled explicitly

TL,DR: there are many circumstances when `^C` won't stop the container.

.debug[[containers/Background_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Background_Containers.md)]
---

## Why is PID 1 special?

- PID 1 has some extra responsibilities:

- it starts (directly or indirectly) every other process

- when a process exits, its processes are "reparented" under PID 1

- When PID 1 exits, everything stops:

- on a "regular" machine, it causes a kernel panic

- in a container, it kills all the processes

- We don't want PID 1 to stop accidentally

- That's why it has these extra protections

.debug[[containers/Background_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Background_Containers.md)]
---

## How to stop these containers, then?

- Start another terminal and forget about them

(for now!)

- We'll shortly learn about `docker kill`

.debug[[containers/Background_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Background_Containers.md)]
---

## Run a container in the background

Containers can be started in the background, with the `-d` flag (daemon mode):

```bash
$ docker run -d jpetazzo/clock
47d677dcfba4277c6cc68fcaa51f932b544cab1a187c853b7d0caf4e8debe5ad
```

* We don't see the output of the container.
* But don't worry: Docker collects that output and logs it!
* Docker gives us the ID of the container.

.debug[[containers/Background_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Background_Containers.md)]
---

## List running containers

How can we check that our container is still running?

With `docker ps`, just like the UNIX `ps` command, lists running processes.

```bash
$ docker ps
CONTAINER ID  IMAGE           ...  CREATED        STATUS        ...
47d677dcfba4  jpetazzo/clock  ...  2 minutes ago  Up 2 minutes  ...
```

Docker tells us:

* The (truncated) ID of our container.
* The image used to start the container.
* That our container has been running (`Up`) for a couple of minutes.
* Other information (COMMAND, PORTS, NAMES) that we will explain later.

.debug[[containers/Background_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Background_Containers.md)]
---

## Starting more containers

Let's start two more containers.

```bash
$ docker run -d jpetazzo/clock
57ad9bdfc06bb4407c47220cf59ce21585dce9a1298d7a67488359aeaea8ae2a
```

```bash
$ docker run -d jpetazzo/clock
068cc994ffd0190bbe025ba74e4c0771a5d8f14734af772ddee8dc1aaf20567d
```

Check that `docker ps` correctly reports all 3 containers.

.debug[[containers/Background_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Background_Containers.md)]
---

## Viewing only the last container started

When many containers are already running, it can be useful to
see only the last container that was started.

This can be achieved with the `-l` ("Last") flag:

```bash
$ docker ps -l
CONTAINER ID  IMAGE           ...  CREATED        STATUS        ...
068cc994ffd0  jpetazzo/clock  ...  2 minutes ago  Up 2 minutes  ...
```

.debug[[containers/Background_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Background_Containers.md)]
---

## View only the IDs of the containers

Many Docker commands will work on container IDs: `docker stop`, `docker rm`...

If we want to list only the IDs of our containers (without the other columns
or the header line),
we can use the `-q` ("Quiet", "Quick") flag:

```bash
$ docker ps -q
068cc994ffd0
57ad9bdfc06b
47d677dcfba4
```

.debug[[containers/Background_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Background_Containers.md)]
---

## Combining flags

We can combine `-l` and `-q` to see only the ID of the last container started:

```bash
$ docker ps -lq
068cc994ffd0
```

At a first glance, it looks like this would be particularly useful in scripts.

However, if we want to start a container and get its ID in a reliable way,
it is better to use `docker run -d`, which we will cover in a bit.

(Using `docker ps -lq` is prone to race conditions: what happens if someone
else, or another program or script, starts another container just before
we run `docker ps -lq`?)

.debug[[containers/Background_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Background_Containers.md)]
---

## View the logs of a container

We told you that Docker was logging the container output.

Let's see that now.

```bash
$ docker logs 068
Fri Feb 20 00:39:52 UTC 2015
Fri Feb 20 00:39:53 UTC 2015
...
```

* We specified a *prefix* of the full container ID.
* You can, of course, specify the full ID.
* The `logs` command will output the *entire* logs of the container.
 (Sometimes, that will be too much. Let's see how to address that.)

.debug[[containers/Background_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Background_Containers.md)]
---

## View only the tail of the logs

To avoid being spammed with eleventy pages of output,
we can use the `--tail` option:

```bash
$ docker logs --tail 3 068
Fri Feb 20 00:55:35 UTC 2015
Fri Feb 20 00:55:36 UTC 2015
Fri Feb 20 00:55:37 UTC 2015
```

* The parameter is the number of lines that we want to see.

.debug[[containers/Background_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Background_Containers.md)]
---

## Follow the logs in real time

Just like with the standard UNIX command `tail -f`, we can
follow the logs of our container:

```bash
$ docker logs --tail 1 --follow 068
Fri Feb 20 00:57:12 UTC 2015
Fri Feb 20 00:57:13 UTC 2015
^C
```

* This will display the last line in the log file.
* Then, it will continue to display the logs in real time.
* Use `^C` to exit.

.debug[[containers/Background_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Background_Containers.md)]
---

## Stop our container

There are two ways we can terminate our detached container.

* Killing it using the `docker kill` command.
* Stopping it using the `docker stop` command.

The first one stops the container immediately, by using the
`KILL` signal.

The second one is more graceful. It sends a `TERM` signal,
and after 10 seconds, if the container has not stopped, it
sends `KILL.`

Reminder: the `KILL` signal cannot be intercepted, and will
forcibly terminate the container.

.debug[[containers/Background_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Background_Containers.md)]
---

## Stopping our containers

Let's stop one of those containers:

```bash
$ docker stop 47d6
47d6
```

This will take 10 seconds:

* Docker sends the TERM signal;
* the container doesn't react to this signal
  (it's a simple Shell script with no special
  signal handling);
* 10 seconds later, since the container is still
  running, Docker sends the KILL signal;
* this terminates the container.

.debug[[containers/Background_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Background_Containers.md)]
---

## Killing the remaining containers

Let's be less patient with the two other containers:

```bash
$ docker kill 068 57ad
068
57ad
```

The `stop` and `kill` commands can take multiple container IDs.

Those containers will be terminated immediately (without
the 10-second delay).

Let's check that our containers don't show up anymore:

```bash
$ docker ps
```

.debug[[containers/Background_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Background_Containers.md)]
---

## List stopped containers

We can also see stopped containers, with the `-a` (`--all`) option.

```bash
$ docker ps -a
CONTAINER ID  IMAGE           ...  CREATED      STATUS
068cc994ffd0  jpetazzo/clock  ...  21 min. ago  Exited (137) 3 min. ago
57ad9bdfc06b  jpetazzo/clock  ...  21 min. ago  Exited (137) 3 min. ago
47d677dcfba4  jpetazzo/clock  ...  23 min. ago  Exited (137) 3 min. ago
5c1dfd4d81f1  jpetazzo/clock  ...  40 min. ago  Exited (0) 40 min. ago
b13c164401fb  ubuntu          ...  55 min. ago  Exited (130) 53 min. ago
```

???

:EN:- Foreground and background containers
:FR:- Exécution interactive ou en arrière-plan

.debug[[containers/Background_Containers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Background_Containers.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/blue-containers.jpg)]

---

Understanding Docker images

.nav[
[Previous part](#toc-background-containers)
|
[Back to table of contents](#toc-part-1)
|
[Next part](#toc-building-images-interactively)
]

---

# Understanding Docker images

![image](images/title-understanding-docker-images.png)

.debug[[containers/Initial_Images.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Initial_Images.md)]
---

## Objectives

In this section, we will explain:

* What is an image.

* What is a layer.

* The various image namespaces.

* How to search and download images.

* Image tags and when to use them.

.debug[[containers/Initial_Images.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Initial_Images.md)]
---

## What is an image?

* Image = files + metadata

* These files form the root filesystem of our container.

* The metadata can indicate a number of things, e.g.:

* the author of the image
  * the command to execute in the container when starting it
  * environment variables to be set
  * etc.

* Images are made of *layers*, conceptually stacked on top of each other.

* Each layer can add, change, and remove files and/or metadata.

* Images can share layers to optimize disk usage, transfer times, and memory use.

.debug[[containers/Initial_Images.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Initial_Images.md)]
---

## Example for a Java webapp

Each of the following items will correspond to one layer:

* CentOS base layer
* Packages and configuration files added by our local IT
* JRE
* Tomcat
* Our application's dependencies
* Our application code and assets
* Our application configuration

(Note: app config is generally added by orchestration facilities.)

.debug[[containers/Initial_Images.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Initial_Images.md)]
---

## The read-write layer

![layers](images/container-layers.jpg)

.debug[[containers/Initial_Images.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Initial_Images.md)]
---

## Differences between containers and images

* An image is a read-only filesystem.

* A container is an encapsulated set of processes,

running in a read-write copy of that filesystem.

* To optimize container boot time, *copy-on-write* is used
  instead of regular copy.

* `docker run` starts a container from a given image.

.debug[[containers/Initial_Images.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Initial_Images.md)]
---

## Multiple containers sharing the same image

![layers](images/sharing-layers.jpg)

.debug[[containers/Initial_Images.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Initial_Images.md)]
---

## Comparison with object-oriented programming

* Images are conceptually similar to *classes*.

* Layers are conceptually similar to *inheritance*.

* Containers are conceptually similar to *instances*.

.debug[[containers/Initial_Images.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Initial_Images.md)]
---

## Wait a minute...

If an image is read-only, how do we change it?

* We don't.

* We create a new container from that image.

* Then we make changes to that container.

* When we are satisfied with those changes, we transform them into a new layer.

* A new image is created by stacking the new layer on top of the old image.

.debug[[containers/Initial_Images.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Initial_Images.md)]
---

## A chicken-and-egg problem

* The only way to create an image is by "freezing" a container.

* The only way to create a container is by instantiating an image.

* Help!

.debug[[containers/Initial_Images.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Initial_Images.md)]
---

## Creating the first images

There is a special empty image called `scratch`.

* It allows to *build from scratch*.

The `docker import` command loads a tarball into Docker.

* The imported tarball becomes a standalone image.
* That new image has a single layer.

Note: you will probably never have to do this yourself.

.debug[[containers/Initial_Images.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Initial_Images.md)]
---

## Creating other images

`docker commit`

* Saves all the changes made to a container into a new layer.
* Creates a new image (effectively a copy of the container).

`docker build` **(used 99% of the time)**

* Performs a repeatable build sequence.
* This is the preferred method!

We will explain both methods in a moment.

.debug[[containers/Initial_Images.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Initial_Images.md)]
---

## Images namespaces

There are three namespaces:

* Official images

e.g. `ubuntu`, `busybox` ...

* User (and organizations) images

e.g. `jpetazzo/clock`

* Self-hosted images

e.g. `registry.example.com:5000/my-private/image`

Let's explain each of them.

.debug[[containers/Initial_Images.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Initial_Images.md)]
---

## Root namespace

The root namespace is for official images.

They are gated by Docker Inc.

They are generally authored and maintained by third parties.

Those images include:

* Small, "swiss-army-knife" images like busybox.

* Distro images to be used as bases for your builds, like ubuntu, fedora...

* Ready-to-use components and services, like redis, postgresql...

* Over 150 at this point!

.debug[[containers/Initial_Images.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Initial_Images.md)]
---

## User namespace

The user namespace holds images for Docker Hub users and organizations.

For example:

```bash
jpetazzo/clock
```

The Docker Hub user is:

```bash
jpetazzo
```

The image name is:

```bash
clock
```

.debug[[containers/Initial_Images.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Initial_Images.md)]
---

## Self-hosted namespace

This namespace holds images which are not hosted on Docker Hub, but on third
party registries.

They contain the hostname (or IP address), and optionally the port, of the
registry server.

For example:

```bash
localhost:5000/wordpress
```

* `localhost:5000` is the host and port of the registry
* `wordpress` is the name of the image

Other examples:

```bash
quay.io/coreos/etcd
gcr.io/google-containers/hugo
```

.debug[[containers/Initial_Images.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Initial_Images.md)]
---

## How do you store and manage images?

Images can be stored:

* On your Docker host.
* In a Docker registry.

You can use the Docker client to download (pull) or upload (push) images.

To be more accurate: you can use the Docker client to tell a Docker Engine
to push and pull images to and from a registry.

.debug[[containers/Initial_Images.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Initial_Images.md)]
---

## Showing current images

Let's look at what images are on our host now.

```bash
$ docker images
REPOSITORY       TAG       IMAGE ID       CREATED         SIZE
fedora           latest    ddd5c9c1d0f2   3 days ago      204.7 MB
centos           latest    d0e7f81ca65c   3 days ago      196.6 MB
ubuntu           latest    07c86167cdc4   4 days ago      188 MB
redis            latest    4f5f397d4b7c   5 days ago      177.6 MB
postgres         latest    afe2b5e1859b   5 days ago      264.5 MB
alpine           latest    70c557e50ed6   5 days ago      4.798 MB
debian           latest    f50f9524513f   6 days ago      125.1 MB
busybox          latest    3240943c9ea3   2 weeks ago     1.114 MB
training/namer   latest    902673acc741   9 months ago    289.3 MB
jpetazzo/clock   latest    12068b93616f   12 months ago   2.433 MB
```

.debug[[containers/Initial_Images.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Initial_Images.md)]
---

## Searching for images

We cannot list *all* images on a remote registry, but
we can search for a specific keyword:

```bash
$ docker search marathon
NAME                     DESCRIPTION                     STARS  OFFICIAL  AUTOMATED
mesosphere/marathon      A cluster-wide init and co...   105              [OK]
mesoscloud/marathon      Marathon                        31               [OK]
mesosphere/marathon-lb   Script to update haproxy b...   22               [OK]
tobilg/mongodb-marathon  A Docker image to start a ...   4                [OK]
```

* "Stars" indicate the popularity of the image.

* "Official" images are those in the root namespace.

* "Automated" images are built automatically by the Docker Hub.
 (This means that their build recipe is always available.)

.debug[[containers/Initial_Images.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Initial_Images.md)]
---

## Downloading images

There are two ways to download images.

* Explicitly, with `docker pull`.

* Implicitly, when executing `docker run` and the image is not found locally.

.debug[[containers/Initial_Images.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Initial_Images.md)]
---

## Pulling an image

```bash
$ docker pull debian:jessie
Pulling repository debian
b164861940b8: Download complete
b164861940b8: Pulling image (jessie) from debian
d1881793a057: Download complete
```

* As seen previously, images are made up of layers.

* Docker has downloaded all the necessary layers.

* In this example, `:jessie` indicates which exact version of Debian
  we would like.

It is a *version tag*.

.debug[[containers/Initial_Images.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Initial_Images.md)]
---

## Image and tags

* Images can have tags.

* Tags define image versions or variants.

* `docker pull ubuntu` will refer to `ubuntu:latest`.

* The `:latest` tag is generally updated often.

.debug[[containers/Initial_Images.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Initial_Images.md)]
---

## When to (not) use tags

Don't specify tags:

* When doing rapid testing and prototyping.
* When experimenting.
* When you want the latest version.

Do specify tags:

* When recording a procedure into a script.
* When going to production.
* To ensure that the same version will be used everywhere.
* To ensure repeatability later.

This is similar to what we would do with `pip install`, `npm install`, etc.

.debug[[containers/Initial_Images.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Initial_Images.md)]
---

## Multi-arch images

- An image can support multiple architectures

- More precisely, a specific *tag* in a given *repository* can have either:

- a single *manifest* referencing an image for a single architecture

- a *manifest list* (or *fat manifest*) referencing multiple images

- In a *manifest list*, each image is identified by a combination of:

- `os` (linux, windows)

- `architecture` (amd64, arm, arm64...)

- optional fields like `variant` (for arm and arm64), `os.version` (for windows)

.debug[[containers/Initial_Images.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Initial_Images.md)]
---

## Working with multi-arch images

- The Docker Engine will pull "native" images when available

(images matching its own os/architecture/variant)

- We can ask for a specific image platform with `--platform`

- The Docker Engine can run non-native images thanks to QEMU+binfmt

(automatically on Docker Desktop; with a bit of setup on Linux)

.debug[[containers/Initial_Images.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Initial_Images.md)]
---

## Section summary

We've learned how to:

* Understand images and layers.
* Understand Docker image namespacing.
* Search and download images.

???

:EN:Building images
:EN:- Containers, images, and layers
:EN:- Image addresses and tags
:EN:- Finding and transferring images

:FR:Construire des images
:FR:- La différence entre un conteneur et une image
:FR:- La notion de *layer* partagé entre images

.debug[[containers/Initial_Images.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Initial_Images.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/chinook-helicopter-container.jpg)]

---

Building images interactively

.nav[
[Previous part](#toc-understanding-docker-images)
|
[Back to table of contents](#toc-part-1)
|
[Next part](#toc-building-docker-images-with-a-dockerfile)
]

---
# Building images interactively

In this section, we will create our first container image.

It will be a basic distribution image, but we will pre-install
the package `figlet`.

We will:

* Create a container from a base image.

* Install software manually in the container, and turn it
  into a new image.

* Learn about new commands: `docker commit`, `docker tag`, and `docker diff`.

.debug[[containers/Building_Images_Interactively.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_Interactively.md)]
---

## The plan

1. Create a container (with `docker run`) using our base distro of choice.

2. Run a bunch of commands to install and set up our software in the container.

3. (Optionally) review changes in the container with `docker diff`.

4. Turn the container into a new image with `docker commit`.

5. (Optionally) add tags to the image with `docker tag`.

.debug[[containers/Building_Images_Interactively.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_Interactively.md)]
---

## Setting up our container

Start an Ubuntu container:

```bash
$ docker run -it ubuntu
root@<yourContainerId>:#/
```

Run the command `apt-get update` to refresh the list of packages available to install.

Then run the command `apt-get install figlet` to install the program we are interested in.

```bash
root@<yourContainerId>:#/ apt-get update && apt-get install figlet
.... OUTPUT OF APT-GET COMMANDS ....
```

.debug[[containers/Building_Images_Interactively.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_Interactively.md)]
---

## Inspect the changes

Type `exit` at the container prompt to leave the interactive session.

Now let's run `docker diff` to see the difference between the base image
and our container.

```bash
$ docker diff <yourContainerId>
C /root
A /root/.bash_history
C /tmp
C /usr
C /usr/bin
A /usr/bin/figlet
...
```

.debug[[containers/Building_Images_Interactively.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_Interactively.md)]
---

## Docker tracks filesystem changes

As explained before:

* An image is read-only.

* When we make changes, they happen in a copy of the image.

* Docker can show the difference between the image, and its copy.

* For performance, Docker uses copy-on-write systems.
 (i.e. starting a container based on a big image
 doesn't incur a huge copy.)

.debug[[containers/Building_Images_Interactively.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_Interactively.md)]
---

## Copy-on-write security benefits

* `docker diff` gives us an easy way to audit changes

(à la Tripwire)

* Containers can also be started in read-only mode

(their root filesystem will be read-only, but they can still have read-write data volumes)

.debug[[containers/Building_Images_Interactively.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_Interactively.md)]
---

## Commit our changes into a new image

The `docker commit` command will create a new layer with those changes,
and a new image using this new layer.

```bash
$ docker commit <yourContainerId>
<newImageId>
```

The output of the `docker commit` command will be the ID for your newly created image.

We can use it as an argument to `docker run`.

.debug[[containers/Building_Images_Interactively.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_Interactively.md)]
---

## Testing our new image

Let's run this image:

```bash
$ docker run -it <newImageId>
root@fcfb62f0bfde:/# figlet hello
 _ _ _ 
| |__ ___| | | ___ 
| '_ \ / _ \ | |/ _ \ 
| | | | __/ | | (_) |
|_| |_|\___|_|_|\___/ 
```

It works! 🎉

.debug[[containers/Building_Images_Interactively.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_Interactively.md)]
---

## Tagging images

Referring to an image by its ID is not convenient. Let's tag it instead.

We can use the `tag` command:

```bash
$ docker tag <newImageId> figlet
```

But we can also specify the tag as an extra argument to `commit`:

```bash
$ docker commit <containerId> figlet
```

And then run it using its tag:

```bash
$ docker run -it figlet
```

.debug[[containers/Building_Images_Interactively.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_Interactively.md)]
---

## What's next?

Manual process = bad.

Automated process = good.

In the next chapter, we will learn how to automate the build
process by writing a `Dockerfile`.

???

:EN:- Building our first images interactively
:FR:- Fabriquer nos premières images à la main

.debug[[containers/Building_Images_Interactively.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_Interactively.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/container-cranes.jpg)]

---

Building Docker images with a Dockerfile

.nav[
[Previous part](#toc-building-images-interactively)
|
[Back to table of contents](#toc-part-1)
|
[Next part](#toc-cmd-and-entrypoint)
]

---

# Building Docker images with a Dockerfile

![Construction site with containers](images/title-building-docker-images-with-a-dockerfile.jpg)

.debug[[containers/Building_Images_With_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_With_Dockerfiles.md)]
---

## Objectives

We will build a container image automatically, with a `Dockerfile`.

At the end of this lesson, you will be able to:

* Write a `Dockerfile`.

* Build an image from a `Dockerfile`.

.debug[[containers/Building_Images_With_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_With_Dockerfiles.md)]
---

## `Dockerfile` overview

* A `Dockerfile` is a build recipe for a Docker image.

* It contains a series of instructions telling Docker how an image is constructed.

* The `docker build` command builds an image from a `Dockerfile`.

.debug[[containers/Building_Images_With_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_With_Dockerfiles.md)]
---

## Writing our first `Dockerfile`

Our Dockerfile must be in a **new, empty directory**.

1. Create a directory to hold our `Dockerfile`.

```bash
$ mkdir myimage
```

2. Create a `Dockerfile` inside this directory.

```bash
$ cd myimage
$ vim Dockerfile
```

Of course, you can use any other editor of your choice.

.debug[[containers/Building_Images_With_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_With_Dockerfiles.md)]
---

## Type this into our Dockerfile...

```dockerfile
FROM ubuntu
RUN apt-get update
RUN apt-get install figlet
```

* `FROM` indicates the base image for our build.

* Each `RUN` line will be executed by Docker during the build.

* Our `RUN` commands **must be non-interactive.**
 (No input can be provided to Docker during the build.)

* In many cases, we will add the `-y` flag to `apt-get`.

.debug[[containers/Building_Images_With_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_With_Dockerfiles.md)]
---

## Build it!

Save our file, then execute:

```bash
$ docker build -t figlet .
```

* `-t` indicates the tag to apply to the image.

* `.` indicates the location of the *build context*.

We will talk more about the build context later.

To keep things simple for now: this is the directory where our Dockerfile is located.

.debug[[containers/Building_Images_With_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_With_Dockerfiles.md)]
---

## What happens when we build the image?

It depends if we're using BuildKit or not!

If there are lots of blue lines and the first line looks like this:
```
[+] Building 1.8s (4/6)
```
... then we're using BuildKit.

If the output is mostly black-and-white and the first line looks like this:
```
Sending build context to Docker daemon  2.048kB
```
... then we're using the "classic" or "old-style" builder.

.debug[[containers/Building_Images_With_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_With_Dockerfiles.md)]
---

## To BuildKit or Not To BuildKit

Classic builder:

- copies the whole "build context" to the Docker Engine

- linear (processes lines one after the other)

- requires a full Docker Engine

BuildKit:

- only transfers parts of the "build context" when needed

- will parallelize operations (when possible)

- can run in non-privileged containers (e.g. on Kubernetes)

.debug[[containers/Building_Images_With_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_With_Dockerfiles.md)]
---

## With the classic builder

The output of `docker build` looks like this:

.small[
```bash
docker build -t figlet .
Sending build context to Docker daemon  2.048kB
Step 1/3 : FROM ubuntu
 ---> f975c5035748
Step 2/3 : RUN apt-get update
 ---> Running in e01b294dbffd
(...output of the RUN command...)
Removing intermediate container e01b294dbffd
 ---> eb8d9b561b37
Step 3/3 : RUN apt-get install figlet
 ---> Running in c29230d70f9b
(...output of the RUN command...)
Removing intermediate container c29230d70f9b
 ---> 0dfd7a253f21
Successfully built 0dfd7a253f21
Successfully tagged figlet:latest
```
]

* The output of the `RUN` commands has been omitted.
* Let's explain what this output means.

.debug[[containers/Building_Images_With_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_With_Dockerfiles.md)]
---

## Sending the build context to Docker

```bash
Sending build context to Docker daemon 2.048 kB
```

* The build context is the `.` directory given to `docker build`.

* It is sent (as an archive) by the Docker client to the Docker daemon.

* This allows to use a remote machine to build using local files.

* Be careful (or patient) if that directory is big and your link is slow.

* You can speed up the process with a [`.dockerignore`](https://docs.docker.com/engine/reference/builder/#dockerignore-file) file

* It tells docker to ignore specific files in the directory

* Only ignore files that you won't need in the build context!

.debug[[containers/Building_Images_With_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_With_Dockerfiles.md)]
---

## Executing each step

```bash
Step 2/3 : RUN apt-get update
 ---> Running in e01b294dbffd
(...output of the RUN command...)
Removing intermediate container e01b294dbffd
 ---> eb8d9b561b37
```

* A container (`e01b294dbffd`) is created from the base image.

* The `RUN` command is executed in this container.

* The container is committed into an image (`eb8d9b561b37`).

* The build container (`e01b294dbffd`) is removed.

* The output of this step will be the base image for the next one.

.debug[[containers/Building_Images_With_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_With_Dockerfiles.md)]
---

## With BuildKit

.small[
```bash
[+] Building 7.9s (7/7) FINISHED
 => [internal] load build definition from Dockerfile                                                 0.0s
 => => transferring dockerfile: 98B                                                                  0.0s
 => [internal] load .dockerignore                                                                    0.0s
 => => transferring context: 2B                                                                      0.0s
 => [internal] load metadata for docker.io/library/ubuntu:latest                                     1.2s
 => [1/3] FROM docker.io/library/ubuntu@sha256:cf31af331f38d1d7158470e095b132acd126a7180a54f263d386  3.2s
 => => resolve docker.io/library/ubuntu@sha256:cf31af331f38d1d7158470e095b132acd126a7180a54f263d386  0.0s
 => => sha256:cf31af331f38d1d7158470e095b132acd126a7180a54f263d386da88eb681d93 1.20kB / 1.20kB       0.0s
 => => sha256:1de4c5e2d8954bf5fa9855f8b4c9d3c3b97d1d380efe19f60f3e4107a66f5cae 943B / 943B           0.0s
 => => sha256:6a98cbe39225dadebcaa04e21dbe5900ad604739b07a9fa351dd10a6ebad4c1b 3.31kB / 3.31kB       0.0s
 => => sha256:80bc30679ac1fd798f3241208c14accd6a364cb8a6224d1127dfb1577d10554f 27.14MB / 27.14MB     2.3s
 => => sha256:9bf18fab4cfbf479fa9f8409ad47e2702c63241304c2cdd4c33f2a1633c5f85e 850B / 850B           0.5s
 => => sha256:5979309c983a2adeff352538937475cf961d49c34194fa2aab142effe19ed9c1 189B / 189B           0.4s
 => => extracting sha256:80bc30679ac1fd798f3241208c14accd6a364cb8a6224d1127dfb1577d10554f            0.7s
 => => extracting sha256:9bf18fab4cfbf479fa9f8409ad47e2702c63241304c2cdd4c33f2a1633c5f85e            0.0s
 => => extracting sha256:5979309c983a2adeff352538937475cf961d49c34194fa2aab142effe19ed9c1            0.0s
 => [2/3] RUN apt-get update                                                                         2.5s
 => [3/3] RUN apt-get install figlet                                                                 0.9s
 => exporting to image                                                                               0.1s
 => => exporting layers                                                                              0.1s
 => => writing image sha256:3b8aee7b444ab775975dfba691a72d8ac24af2756e0a024e056e3858d5a23f7c         0.0s
 => => naming to docker.io/library/figlet                                                            0.0s
 ```
 ]

.debug[[containers/Building_Images_With_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_With_Dockerfiles.md)]
---

## Understanding BuildKit output

- BuildKit transfers the Dockerfile and the *build context*

(these are the first two `[internal]` stages)

- Then it executes the steps defined in the Dockerfile

(`[1/3]`, `[2/3]`, `[3/3]`)

- Finally, it exports the result of the build

(image definition + collection of layers)

.debug[[containers/Building_Images_With_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_With_Dockerfiles.md)]
---

## BuildKit plain output

- When running BuildKit in e.g. a CI pipeline, its output will be different

- We can see the same output format by using `--progress=plain`

.debug[[containers/Building_Images_With_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_With_Dockerfiles.md)]
---

## The caching system

If you run the same build again, it will be instantaneous. Why?

* After each build step, Docker takes a snapshot of the resulting image.

* Before executing a step, Docker checks if it has already built the same sequence.

* Docker uses the exact strings defined in your Dockerfile, so:

* `RUN apt-get install figlet cowsay`
 is different from
 `RUN apt-get install cowsay figlet`

* `RUN apt-get update` is not re-executed when the mirrors are updated

You can force a rebuild with `docker build --no-cache ...`.

.debug[[containers/Building_Images_With_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_With_Dockerfiles.md)]
---

## Running the image

The resulting image is not different from the one produced manually.

```bash
$ docker run -ti figlet
root@91f3c974c9a1:/# figlet hello
 _          _ _       
| |__   ___| | | ___  
| '_ \ / _ \ | |/ _ \ 
| | | |  __/ | | (_) |
|_| |_|\___|_|_|\___/ 
```

Yay! 🎉

.debug[[containers/Building_Images_With_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_With_Dockerfiles.md)]
---

## Using image and viewing history

The `history` command lists all the layers composing an image.

For each layer, it shows its creation time, size, and creation command.

When an image was built with a Dockerfile, each layer corresponds to
a line of the Dockerfile.

```bash
$ docker history figlet
IMAGE CREATED CREATED BY SIZE
f9e8f1642759 About an hour ago /bin/sh -c apt-get install fi 1.627 MB
7257c37726a1 About an hour ago /bin/sh -c apt-get update 21.58 MB
07c86167cdc4 4 days ago /bin/sh -c #(nop) CMD ["/bin 0 B
<missing> 4 days ago /bin/sh -c sed -i 's/^#\s*\( 1.895 kB
<missing> 4 days ago /bin/sh -c echo '#!/bin/sh' 194.5 kB
<missing> 4 days ago /bin/sh -c #(nop) ADD file:b 187.8 MB
```

.debug[[containers/Building_Images_With_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_With_Dockerfiles.md)]
---

## Why `sh -c`?

* On UNIX, to start a new program, we need two system calls:

- `fork()`, to create a new child process;

- `execve()`, to replace the new child process with the program to run.

* Conceptually, `execve()` works like this:

`execve(program, [list, of, arguments])`

* When we run a command, e.g. `ls -l /tmp`, something needs to parse the command.

(i.e. split the program and its arguments into a list.)

* The shell is usually doing that.

(It also takes care of expanding environment variables and special things like `~`.)

.debug[[containers/Building_Images_With_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_With_Dockerfiles.md)]
---

## Why `sh -c`?

* When we do `RUN ls -l /tmp`, the Docker builder needs to parse the command.

* Instead of implementing its own parser, it outsources the job to the shell.

* That's why we see `sh -c ls -l /tmp` in that case.

* But we can also do the parsing jobs ourselves.

* This means passing `RUN` a list of arguments.

* This is called the *exec syntax*.

.debug[[containers/Building_Images_With_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_With_Dockerfiles.md)]
---

## Shell syntax vs exec syntax

Dockerfile commands that execute something can have two forms:

* plain string, or *shell syntax*:
 `RUN apt-get install figlet`

* JSON list, or *exec syntax*:
 `RUN ["apt-get", "install", "figlet"]`

We are going to change our Dockerfile to see how it affects the resulting image.

.debug[[containers/Building_Images_With_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_With_Dockerfiles.md)]
---

## Using exec syntax in our Dockerfile

Let's change our Dockerfile as follows!

```dockerfile
FROM ubuntu
RUN apt-get update
RUN ["apt-get", "install", "figlet"]
```

Then build the new Dockerfile.

```bash
$ docker build -t figlet .
```

.debug[[containers/Building_Images_With_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_With_Dockerfiles.md)]
---

## History with exec syntax

Compare the new history:

```bash
$ docker history figlet
IMAGE CREATED CREATED BY SIZE
27954bb5faaf 10 seconds ago apt-get install figlet 1.627 MB
7257c37726a1 About an hour ago /bin/sh -c apt-get update 21.58 MB
07c86167cdc4 4 days ago /bin/sh -c #(nop) CMD ["/bin 0 B
<missing> 4 days ago /bin/sh -c sed -i 's/^#\s*\( 1.895 kB
<missing> 4 days ago /bin/sh -c echo '#!/bin/sh' 194.5 kB
<missing> 4 days ago /bin/sh -c #(nop) ADD file:b 187.8 MB
```

* Exec syntax specifies an *exact* command to execute.

* Shell syntax specifies a command to be wrapped within `/bin/sh -c "..."`.

.debug[[containers/Building_Images_With_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_With_Dockerfiles.md)]
---

## When to use exec syntax and shell syntax

* shell syntax:

* is easier to write
  * interpolates environment variables and other shell expressions
  * creates an extra process (`/bin/sh -c ...`) to parse the string
  * requires `/bin/sh` to exist in the container

* exec syntax:

* is harder to write (and read!)
  * passes all arguments without extra processing
  * doesn't create an extra process
  * doesn't require `/bin/sh` to exist in the container

.debug[[containers/Building_Images_With_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_With_Dockerfiles.md)]
---

## Pro-tip: the `exec` shell built-in

POSIX shells have a built-in command named `exec`.

`exec` should be followed by a program and its arguments.

From a user perspective:

- it looks like the shell exits right away after the command execution,

- in fact, the shell exits just *before* command execution;

- or rather, the shell gets *replaced* by the command.

.debug[[containers/Building_Images_With_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_With_Dockerfiles.md)]
---

## Example using `exec`

```dockerfile
CMD exec figlet -f script hello
```

In this example, `sh -c` will still be used, but
`figlet` will be PID 1 in the container.

The shell gets replaced by `figlet` when `figlet` starts execution.

This allows to run processes as PID 1 without using JSON.

???

:EN:- Towards automated, reproducible builds
:EN:- Writing our first Dockerfile
:FR:- Rendre le processus automatique et reproductible
:FR:- Écrire son premier Dockerfile

.debug[[containers/Building_Images_With_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Building_Images_With_Dockerfiles.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/container-housing.jpg)]

---

`CMD` and `ENTRYPOINT`

.nav[
[Previous part](#toc-building-docker-images-with-a-dockerfile)
|
[Back to table of contents](#toc-part-1)
|
[Next part](#toc-copying-files-during-the-build)
]

---

# `CMD` and `ENTRYPOINT`

![Container entry doors](images/entrypoint.jpg)

.debug[[containers/Cmd_And_Entrypoint.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Cmd_And_Entrypoint.md)]
---

## Objectives

In this lesson, we will learn about two important
Dockerfile commands:

`CMD` and `ENTRYPOINT`.

These commands allow us to set the default command
to run in a container.

.debug[[containers/Cmd_And_Entrypoint.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Cmd_And_Entrypoint.md)]
---

## Defining a default command

When people run our container, we want to greet them with a nice hello message, and using a custom font.

For that, we will execute:

```bash
figlet -f script hello
```

* `-f script` tells figlet to use a fancy font.

* `hello` is the message that we want it to display.

.debug[[containers/Cmd_And_Entrypoint.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Cmd_And_Entrypoint.md)]
---

## Adding `CMD` to our Dockerfile

Our new Dockerfile will look like this:

```dockerfile
FROM ubuntu
RUN apt-get update
RUN ["apt-get", "install", "figlet"]
CMD figlet -f script hello
```

* `CMD` defines a default command to run when none is given.

* It can appear at any point in the file.

* Each `CMD` will replace and override the previous one.

* As a result, while you can have multiple `CMD` lines, it is useless.

.debug[[containers/Cmd_And_Entrypoint.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Cmd_And_Entrypoint.md)]
---

## Build and test our image

Let's build it:

```bash
$ docker build -t figlet .
...
Successfully built 042dff3b4a8d
Successfully tagged figlet:latest
```

And run it:

```bash
$ docker run figlet
 _          _   _       
| |        | | | |      
| |     _  | | | |  __  
|/ \   |/  |/  |/  /  \_
|   |_/|__/|__/|__/\__/ 
```

.debug[[containers/Cmd_And_Entrypoint.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Cmd_And_Entrypoint.md)]
---

## Overriding `CMD`

If we want to get a shell into our container (instead of running
`figlet`), we just have to specify a different program to run:

```bash
$ docker run -it figlet bash
root@7ac86a641116:/# 
```

* We specified `bash`.

* It replaced the value of `CMD`.

.debug[[containers/Cmd_And_Entrypoint.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Cmd_And_Entrypoint.md)]
---

## Using `ENTRYPOINT`

We want to be able to specify a different message on the command line,
while retaining `figlet` and some default parameters.

In other words, we would like to be able to do this:

```bash
$ docker run figlet salut
           _            
          | |           
 ,   __,  | |       _|_ 
/ \_/  |  |/  |   |  |  
 \/ \_/|_/|__/ \_/|_/|_/
```

We will use the `ENTRYPOINT` verb in Dockerfile.

.debug[[containers/Cmd_And_Entrypoint.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Cmd_And_Entrypoint.md)]
---

## Adding `ENTRYPOINT` to our Dockerfile

Our new Dockerfile will look like this:

```dockerfile
FROM ubuntu
RUN apt-get update
RUN ["apt-get", "install", "figlet"]
ENTRYPOINT ["figlet", "-f", "script"]
```

* `ENTRYPOINT` defines a base command (and its parameters) for the container.

* The command line arguments are appended to those parameters.

* Like `CMD`, `ENTRYPOINT` can appear anywhere, and replaces the previous value.

Why did we use JSON syntax for our `ENTRYPOINT`?

.debug[[containers/Cmd_And_Entrypoint.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Cmd_And_Entrypoint.md)]
---

## Implications of JSON vs string syntax

* When CMD or ENTRYPOINT use string syntax, they get wrapped in `sh -c`.

* To avoid this wrapping, we can use JSON syntax.

What if we used `ENTRYPOINT` with string syntax?

```bash
$ docker run figlet salut
```

This would run the following command in the `figlet` image:

```bash
sh -c "figlet -f script" salut
```

.debug[[containers/Cmd_And_Entrypoint.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Cmd_And_Entrypoint.md)]
---

## Build and test our image

Let's build it:

```bash
$ docker build -t figlet .
...
Successfully built 36f588918d73
Successfully tagged figlet:latest
```

And run it:

```bash
$ docker run figlet salut
           _            
          | |           
 ,   __,  | |       _|_ 
/ \_/  |  |/  |   |  |  
 \/ \_/|_/|__/ \_/|_/|_/
```

.debug[[containers/Cmd_And_Entrypoint.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Cmd_And_Entrypoint.md)]
---

## Using `CMD` and `ENTRYPOINT` together

What if we want to define a default message for our container?

Then we will use `ENTRYPOINT` and `CMD` together.

* `ENTRYPOINT` will define the base command for our container.

* `CMD` will define the default parameter(s) for this command.

* They *both* have to use JSON syntax.

.debug[[containers/Cmd_And_Entrypoint.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Cmd_And_Entrypoint.md)]
---

## `CMD` and `ENTRYPOINT` together

Our new Dockerfile will look like this:

```dockerfile
FROM ubuntu
RUN apt-get update
RUN ["apt-get", "install", "figlet"]
ENTRYPOINT ["figlet", "-f", "script"]
CMD ["hello world"]
```

* `ENTRYPOINT` defines a base command (and its parameters) for the container.

* If we don't specify extra command-line arguments when starting the container,
  the value of `CMD` is appended.

* Otherwise, our extra command-line arguments are used instead of `CMD`.

.debug[[containers/Cmd_And_Entrypoint.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Cmd_And_Entrypoint.md)]
---

## Build and test our image

Let's build it:

```bash
$ docker build -t myfiglet .
...
Successfully built 6e0b6a048a07
Successfully tagged myfiglet:latest
```

Run it without parameters:

```bash
$ docker run myfiglet
 _          _   _                             _        
| |        | | | |                           | |    |  
| |     _  | | | |  __             __   ,_   | |  __|  
|/ \   |/  |/  |/  /  \_  |  |  |_/  \_/  |  |/  /  |  
|   |_/|__/|__/|__/\__/    \/ \/  \__/    |_/|__/\_/|_/
```

.debug[[containers/Cmd_And_Entrypoint.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Cmd_And_Entrypoint.md)]
---

## Overriding the image default parameters

Now let's pass extra arguments to the image.

```bash
$ docker run myfiglet hola mundo
 _           _                                               
| |         | |                                      |       
| |     __  | |  __,     _  _  _           _  _    __|   __  
|/ \   /  \_|/  /  |    / |/ |/ |  |   |  / |/ |  /  |  /  \_
|   |_/\__/ |__/\_/|_/    |  |  |_/ \_/|_/  |  |_/\_/|_/\__/ 
```

We overrode `CMD` but still used `ENTRYPOINT`.

.debug[[containers/Cmd_And_Entrypoint.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Cmd_And_Entrypoint.md)]
---

## Overriding `ENTRYPOINT`

What if we want to run a shell in our container?

We cannot just do `docker run myfiglet bash` because
that would just tell figlet to display the word "bash."

We use the `--entrypoint` parameter:

```bash
$ docker run -it --entrypoint bash myfiglet
root@6027e44e2955:/# 
```

.debug[[containers/Cmd_And_Entrypoint.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Cmd_And_Entrypoint.md)]
---

## `CMD` and `ENTRYPOINT` recap

- `docker run myimage` executes `ENTRYPOINT` + `CMD`

- `docker run myimage args` executes `ENTRYPOINT` + `args` (overriding `CMD`)

- `docker run --entrypoint prog myimage` executes `prog` (overriding both)

.small[
| Command                         | `ENTRYPOINT`       | `CMD`   | Result
|---------------------------------|--------------------|---------|-------
| `docker run figlet`             | none               | none    | Use values from base image (`bash`)
| `docker run figlet hola`        | none               | none    | Error (executable `hola` not found)
| `docker run figlet`             | `figlet -f script` | none    | `figlet -f script`
| `docker run figlet hola`        | `figlet -f script` | none    | `figlet -f script hola`
| `docker run figlet`             | none    | `figlet -f script` | `figlet -f script`
| `docker run figlet hola`        | none    | `figlet -f script` | Error (executable `hola` not found)
| `docker run figlet`             | `figlet -f script` | `hello` | `figlet -f script hello`
| `docker run figlet hola`        | `figlet -f script` | `hello` | `figlet -f script hola`
]

.debug[[containers/Cmd_And_Entrypoint.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Cmd_And_Entrypoint.md)]
---

## When to use `ENTRYPOINT` vs `CMD`

`ENTRYPOINT` is great for "containerized binaries".

Example: `docker run consul --help`

(Pretend that the `docker run` part isn't there!)

`CMD` is great for images with multiple binaries.

Example: `docker run busybox ifconfig`

(It makes sense to indicate *which* program we want to run!)

???

:EN:- CMD and ENTRYPOINT
:FR:- CMD et ENTRYPOINT

.debug[[containers/Cmd_And_Entrypoint.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Cmd_And_Entrypoint.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/containers-by-the-water.jpg)]

---

Copying files during the build

.nav[
[Previous part](#toc-cmd-and-entrypoint)
|
[Back to table of contents](#toc-part-1)
|
[Next part](#toc-exercise--writing-dockerfiles)
]

---

# Copying files during the build

![Monks copying books](images/title-copying-files-during-build.jpg)

.debug[[containers/Copying_Files_During_Build.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Copying_Files_During_Build.md)]
---

## Objectives

So far, we have installed things in our container images
by downloading packages.

We can also copy files from the *build context* to the
container that we are building.

Remember: the *build context* is the directory containing
the Dockerfile.

In this chapter, we will learn a new Dockerfile keyword: `COPY`.

.debug[[containers/Copying_Files_During_Build.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Copying_Files_During_Build.md)]
---

## Build some C code

We want to build a container that compiles a basic "Hello world" program in C.

Here is the program, `hello.c`:

```bash
int main () {
  puts("Hello, world!");
  return 0;
}
```

Let's create a new directory, and put this file in there.

Then we will write the Dockerfile.

.debug[[containers/Copying_Files_During_Build.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Copying_Files_During_Build.md)]
---

## The Dockerfile

On Debian and Ubuntu, the package `build-essential` will get us a compiler.

When installing it, don't forget to specify the `-y` flag, otherwise the build will fail (since the build cannot be interactive).

Then we will use `COPY` to place the source file into the container.

```bash
FROM ubuntu
RUN apt-get update
RUN apt-get install -y build-essential
COPY hello.c /
RUN make hello
CMD /hello
```

Create this Dockerfile.

.debug[[containers/Copying_Files_During_Build.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Copying_Files_During_Build.md)]
---

## Testing our C program

* Create `hello.c` and `Dockerfile` in the same directory.

* Run `docker build -t hello .` in this directory.

* Run `docker run hello`, you should see `Hello, world!`.

Success!

.debug[[containers/Copying_Files_During_Build.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Copying_Files_During_Build.md)]
---

## `COPY` and the build cache

* Run the build again.

* Now, modify `hello.c` and run the build again.

* Docker can cache steps involving `COPY`.

* Those steps will not be executed again if the files haven't been changed.

.debug[[containers/Copying_Files_During_Build.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Copying_Files_During_Build.md)]
---

## Details

* We can `COPY` whole directories recursively

* It is possible to do e.g. `COPY . .`

(but it might require some extra precautions to avoid copying too much)
 
* In older Dockerfiles, you might see the `ADD` command; consider it deprecated

(it is similar to `COPY` but can automatically extract archives)

* If we really wanted to compile C code in a container, we would:

* place it in a different directory, with the `WORKDIR` instruction

* even better, use the `gcc` official image

.debug[[containers/Copying_Files_During_Build.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Copying_Files_During_Build.md)]
---

## `.dockerignore`

- We can create a file named `.dockerignore`

(at the top-level of the build context)

- It can contain file names and globs to ignore

- They won't be sent to the builder

(and won't end up in the resulting image)

- See the [documentation] for the little details

(exceptions can be made with `!`, multiple directory levels with `**`...)

[documentation]: https://docs.docker.com/engine/reference/builder/#dockerignore-file

???

:EN:- Leveraging the build cache for faster builds
:FR:- Tirer parti du cache afin d'optimiser la vitesse de *build*

.debug[[containers/Copying_Files_During_Build.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Copying_Files_During_Build.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/distillery-containers.jpg)]

---

Exercise — writing Dockerfiles

.nav[
[Previous part](#toc-copying-files-during-the-build)
|
[Back to table of contents](#toc-part-1)
|
[Next part](#toc-container-networking-basics)
]

---
# Exercise — writing Dockerfiles

Let's write Dockerfiles for an existing application!

1. Check out the code repository

2. Read all the instructions

3. Write Dockerfiles

4. Build and test them individually

.debug[[containers/Exercise_Dockerfile_Basic.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Exercise_Dockerfile_Basic.md)]
---

## Code repository

Clone the repository available at:

https://github.com/jpetazzo/wordsmith

It should look like this:
```
├── LICENSE
├── README
├── db/
│   └── words.sql
├── web/
│   ├── dispatcher.go
│   └── static/
└── words/
    ├── pom.xml
    └── src/
```

.debug[[containers/Exercise_Dockerfile_Basic.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Exercise_Dockerfile_Basic.md)]
---

## Instructions

The repository contains instructions in English and French.
 
For now, we only care about the first part (about writing Dockerfiles).
 
Place each Dockerfile in its own directory, like this:
```
├── LICENSE
├── README
├── db/
│ ├── `Dockerfile`
│ └── words.sql
├── web/
│ ├── `Dockerfile`
│ ├── dispatcher.go
│ └── static/
└── words/
 ├── `Dockerfile`
 ├── pom.xml
 └── src/
```

.debug[[containers/Exercise_Dockerfile_Basic.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Exercise_Dockerfile_Basic.md)]
---

## Build and test

Build and run each Dockerfile individually.

For `db`, we should be able to see some messages confirming that the data set
was loaded successfully (some `INSERT` lines in the container output).

For `web` and `words`, we should be able to see some message looking like
"server started successfully".

That's all we care about for now!

Bonus question: make sure that each container stops correctly when hitting Ctrl-C.

???

## Test with a Compose file

Place the following Compose file at the root of the repository:

```yaml
version: "3"
services:
  db:
    build: db
  words:
    build: words
  web:
    build: web
    ports:
    - 8888:80
```

Test the whole app by bringin up the stack and connecting to port 8888.

.debug[[containers/Exercise_Dockerfile_Basic.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Exercise_Dockerfile_Basic.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/lots-of-containers.jpg)]

---

Container networking basics

.nav[
[Previous part](#toc-exercise--writing-dockerfiles)
|
[Back to table of contents](#toc-part-2)
|
[Next part](#toc-local-development-workflow-with-docker)
]

---

# Container networking basics

![A dense graph network](images/title-container-networking-basics.jpg)

.debug[[containers/Container_Networking_Basics.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Networking_Basics.md)]
---

## Objectives

We will now run network services (accepting requests) in containers.

At the end of this section, you will be able to:

* Run a network service in a container.

* Connect to that network service.

* Find a container's IP address.

.debug[[containers/Container_Networking_Basics.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Networking_Basics.md)]
---

## Running a very simple service

- We need something small, simple, easy to configure

(or, even better, that doesn't require any configuration at all)

- Let's use the official NGINX image (named `nginx`)

- It runs a static web server listening on port 80

- It serves a default "Welcome to nginx!" page

.debug[[containers/Container_Networking_Basics.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Networking_Basics.md)]
---

## Runing an NGINX server

```bash
$ docker run -d -P nginx
66b1ce719198711292c8f34f84a7b68c3876cf9f67015e752b94e189d35a204e
```

- Docker will automatically pull the `nginx` image from the Docker Hub

- `-d` / `--detach` tells Docker to run it in the background

- `P` / `--publish-all` tells Docker to publish all ports

(publish = make them reachable from other computers)

- ...OK, how do we connect to our web server now?

.debug[[containers/Container_Networking_Basics.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Networking_Basics.md)]
---

## Finding our web server port

- First, we need to find the *port number* used by Docker

(the NGINX container listens on port 80, but this port will be *mapped*)

- We can use `docker ps`:
  ```bash
  $ docker ps
  CONTAINER ID  IMAGE  ...  PORTS                  ...
  e40ffb406c9e  nginx  ...  0.0.0.0:`12345`->80/tcp  ...
  ```

- This means:

*port 12345 on the Docker host is mapped to port 80 in the container*

- Now we need to connect to the Docker host!

.debug[[containers/Container_Networking_Basics.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Networking_Basics.md)]
---

## Finding the address of the Docker host

- When running Docker on your Linux workstation:

*use `localhost`, or any IP address of your machine*

- When running Docker on a remote Linux server:

*use any IP address of the remote machine*

- When running Docker Desktop on Mac or Windows:

*use `localhost`*

- In other scenarios (`docker-machine`, local VM...):

*use the IP address of the Docker VM*
  
.debug[[containers/Container_Networking_Basics.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Networking_Basics.md)]
---

## Connecting to our web server (GUI)

Point your browser to the IP address of your Docker host, on the port
shown by `docker ps` for container port 80.

![Screenshot](images/welcome-to-nginx.png)

.debug[[containers/Container_Networking_Basics.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Networking_Basics.md)]
---

## Connecting to our web server (CLI)

You can also use `curl` directly from the Docker host.

Make sure to use the right port number if it is different
from the example below:

```bash
$ curl localhost:12345
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
...
```

.debug[[containers/Container_Networking_Basics.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Networking_Basics.md)]
---

## How does Docker know which port to map?

* There is metadata in the image telling "this image has something on port 80".

* We can see that metadata with `docker inspect`:

```bash
$ docker inspect --format '{{.Config.ExposedPorts}}' nginx
map[80/tcp:{}]
```

* This metadata was set in the Dockerfile, with the `EXPOSE` keyword.

* We can see that with `docker history`:

```bash
$ docker history nginx
IMAGE CREATED CREATED BY
7f70b30f2cc6 11 days ago /bin/sh -c #(nop) CMD ["nginx" "-g" "…
<missing> 11 days ago /bin/sh -c #(nop) STOPSIGNAL [SIGTERM]
<missing> 11 days ago /bin/sh -c #(nop) EXPOSE 80/tcp
```

.debug[[containers/Container_Networking_Basics.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Networking_Basics.md)]
---

## Why can't we just connect to port 80?

- Our Docker host has only one port 80

- Therefore, we can only have one container at a time on port 80

- Therefore, if multiple containers want port 80, only one can get it

- By default, containers *do not* get "their" port number, but a random one

(not "random" as "crypto random", but as "it depends on various factors")

- We'll see later how to force a port number (including port 80!)

.debug[[containers/Container_Networking_Basics.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Networking_Basics.md)]
---

## Using multiple IP addresses

*Hey, my network-fu is strong, and I have questions...*

- Can I publish one container on 127.0.0.2:80, and another on 127.0.0.3:80?

- My machine has multiple (public) IP addresses, let's say A.A.A.A and B.B.B.B.
 
 Can I have one container on A.A.A.A:80 and another on B.B.B.B:80?

- I have a whole IPV4 subnet, can I allocate it to my containers?

- What about IPV6?

You can do all these things when running Docker directly on Linux.

(On other platforms, *generally not*, but there are some exceptions.)

.debug[[containers/Container_Networking_Basics.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Networking_Basics.md)]
---

## Finding the web server port in a script

Parsing the output of `docker ps` would be painful.

There is a command to help us:

```bash
$ docker port <containerID> 80
0.0.0.0:12345
```

.debug[[containers/Container_Networking_Basics.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Networking_Basics.md)]
---

## Manual allocation of port numbers

If you want to set port numbers yourself, no problem:

```bash
$ docker run -d -p 80:80 nginx
$ docker run -d -p 8000:80 nginx
$ docker run -d -p 8080:80 -p 8888:80 nginx
```

* We are running three NGINX web servers.
* The first one is exposed on port 80.
* The second one is exposed on port 8000.
* The third one is exposed on ports 8080 and 8888.

Note: the convention is `port-on-host:port-on-container`.

.debug[[containers/Container_Networking_Basics.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Networking_Basics.md)]
---

## Plumbing containers into your infrastructure

There are many ways to integrate containers in your network.

* Start the container, letting Docker allocate a public port for it.
 Then retrieve that port number and feed it to your configuration.

* Pick a fixed port number in advance, when you generate your configuration.
 Then start your container by setting the port numbers manually.

* Use an orchestrator like Kubernetes or Swarm.
 The orchestrator will provide its own networking facilities.

Orchestrators typically provide mechanisms to enable direct container-to-container
communication across hosts, and publishing/load balancing for inbound traffic.

.debug[[containers/Container_Networking_Basics.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Networking_Basics.md)]
---

## Finding the container's IP address

We can use the `docker inspect` command to find the IP address of the
container.

```bash
$ docker inspect --format '{{ .NetworkSettings.IPAddress }}' <yourContainerID>
172.17.0.3
```

* `docker inspect` is an advanced command, that can retrieve a ton
  of information about our containers.

* Here, we provide it with a format string to extract exactly the
  private IP address of the container.

.debug[[containers/Container_Networking_Basics.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Networking_Basics.md)]
---

## Pinging our container

Let's try to ping our container *from another container.*

```bash
docker run alpine ping `<ipaddress>`
PING 172.17.0.X (172.17.0.X): 56 data bytes
64 bytes from 172.17.0.X: seq=0 ttl=64 time=0.106 ms
64 bytes from 172.17.0.X: seq=1 ttl=64 time=0.250 ms
64 bytes from 172.17.0.X: seq=2 ttl=64 time=0.188 ms
```

When running on Linux, we can even ping that IP address directly!

(And connect to a container's ports even if they aren't published.)

.debug[[containers/Container_Networking_Basics.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Networking_Basics.md)]
---

## How often do we use `-p` and `-P` ?

- When running a stack of containers, we will often use Compose

- Compose will take care of exposing containers

(through a `ports:` section in the `docker-compose.yml` file)

- It is, however, fairly common to use `docker run -P` for a quick test

- Or `docker run -p ...` when an image doesn't `EXPOSE` a port correctly

.debug[[containers/Container_Networking_Basics.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Networking_Basics.md)]
---

## Section summary

We've learned how to:

* Expose a network port.

* Connect to an application running in a container.

* Find a container's IP address.

???

:EN:- Exposing single containers
:FR:- Exposer un conteneur isolé

.debug[[containers/Container_Networking_Basics.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Networking_Basics.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/plastic-containers.JPG)]

---

Local development workflow with Docker

.nav[
[Previous part](#toc-container-networking-basics)
|
[Back to table of contents](#toc-part-2)
|
[Next part](#toc-the-container-network-model)
]

---

# Local development workflow with Docker

![Construction site](images/title-local-development-workflow-with-docker.jpg)

.debug[[containers/Local_Development_Workflow.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Local_Development_Workflow.md)]
---

## Objectives

At the end of this section, you will be able to:

* Share code between container and host.

* Use a simple local development workflow.

.debug[[containers/Local_Development_Workflow.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Local_Development_Workflow.md)]
---

## Local development in a container

We want to solve the following issues:

- "Works on my machine"

- "Not the same version"

- "Missing dependency"

By using Docker containers, we will get a consistent development environment.

.debug[[containers/Local_Development_Workflow.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Local_Development_Workflow.md)]
---

## Working on the "namer" application

* We have to work on some application whose code is at:

https://github.com/jpetazzo/namer.

* What is it? We don't know yet!

* Let's download the code.

```bash
$ git clone https://github.com/jpetazzo/namer
```

.debug[[containers/Local_Development_Workflow.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Local_Development_Workflow.md)]
---

## Looking at the code

```bash
$ cd namer
$ ls -1
company_name_generator.rb
config.ru
docker-compose.yml
Dockerfile
Gemfile
```

Aha, a `Gemfile`! This is Ruby. Probably. We know this. Maybe?

.debug[[containers/Local_Development_Workflow.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Local_Development_Workflow.md)]
---

## Looking at the `Dockerfile`

```dockerfile
FROM ruby

COPY . /src
WORKDIR /src
RUN bundler install

CMD ["rackup", "--host", "0.0.0.0"]
EXPOSE 9292
```

* This application is using a base `ruby` image.
* The code is copied in `/src`.
* Dependencies are installed with `bundler`.
* The application is started with `rackup`.
* It is listening on port 9292.

.debug[[containers/Local_Development_Workflow.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Local_Development_Workflow.md)]
---

## Building and running the "namer" application

* Let's build the application with the `Dockerfile`!

```bash
$ docker build -t namer .
```

* Then run it. *We need to expose its ports.*

```bash
$ docker run -dP namer
```

* Check on which port the container is listening.

```bash
$ docker ps -l
```

.debug[[containers/Local_Development_Workflow.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Local_Development_Workflow.md)]
---

## Connecting to our application

* Point our browser to our Docker node, on the port allocated to the container.

* Hit "reload" a few times.

* This is an enterprise-class, carrier-grade, ISO-compliant company name generator!

(With 50% more bullshit than the average competition!)

(Wait, was that 50% more, or 50% less? *Anyway!*)

![web application 1](images/webapp-in-blue.png)

.debug[[containers/Local_Development_Workflow.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Local_Development_Workflow.md)]
---

## Making changes to the code

Option 1:

* Edit the code locally
* Rebuild the image
* Re-run the container

Option 2:

* Enter the container (with `docker exec`)
* Install an editor
* Make changes from within the container

Option 3:

* Use a *bind mount* to share local files with the container
* Make changes locally
* Changes are reflected in the container

.debug[[containers/Local_Development_Workflow.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Local_Development_Workflow.md)]
---

## Our first volume

We will tell Docker to map the current directory to `/src` in the container.

```bash
$ docker run -d -v $(pwd):/src -P namer
```

* `-d`: the container should run in detached mode (in the background).

* `-v`: the following host directory should be mounted inside the container.

* `-P`: publish all the ports exposed by this image.

* `namer` is the name of the image we will run.

* We don't specify a command to run because it is already set in the Dockerfile via `CMD`.

Note: on Windows, replace `$(pwd)` with `%cd%` (or `${pwd}` if you use PowerShell).

.debug[[containers/Local_Development_Workflow.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Local_Development_Workflow.md)]
---

## Mounting volumes inside containers

The `-v` flag mounts a directory from your host into your Docker container.

The flag structure is:

```bash
[host-path]:[container-path]:[rw|ro]
```

* `[host-path]` and `[container-path]` are created if they don't exist.

* You can control the write status of the volume with the `ro` and
  `rw` options.

* If you don't specify `rw` or `ro`, it will be `rw` by default.

.debug[[containers/Local_Development_Workflow.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Local_Development_Workflow.md)]
---

## Hold your horses... and your mounts

- The `-v /path/on/host:/path/in/container` syntax is the "old" syntax

- The modern syntax looks like this:

`--mount type=bind,source=/path/on/host,target=/path/in/container`

- `--mount` is more explicit, but `-v` is quicker to type

- `--mount` supports all mount types; `-v` doesn't support `tmpfs` mounts

- `--mount` fails if the path on the host doesn't exist; `-v` creates it

With the new syntax, our command becomes:
```bash
docker run --mount=type=bind,source=$(pwd),target=/src -dP namer
```

.debug[[containers/Local_Development_Workflow.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Local_Development_Workflow.md)]
---

## Testing the development container

* Check the port used by our new container.

```bash
$ docker ps -l
CONTAINER ID  IMAGE  COMMAND  CREATED        STATUS  PORTS                   NAMES
045885b68bc5  namer  rackup   3 seconds ago  Up ...  0.0.0.0:32770->9292/tcp ...
```

* Open the application in your web browser.

.debug[[containers/Local_Development_Workflow.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Local_Development_Workflow.md)]
---

## Making a change to our application

Our customer really doesn't like the color of our text. Let's change it.

```bash
$ vi company_name_generator.rb
```

And change

```css
color: royalblue;
```

To:

```css
color: red;
```

.debug[[containers/Local_Development_Workflow.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Local_Development_Workflow.md)]
---

## Viewing our changes

* Reload the application in our browser.

* The color should have changed.

![web application 2](images/webapp-in-red.png)

.debug[[containers/Local_Development_Workflow.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Local_Development_Workflow.md)]
---

## Understanding volumes

- Volumes are *not* copying or synchronizing files between the host and the container

- Changes made in the host are immediately visible in the container (and vice versa)

- When running on Linux:

- volumes and bind mounts correspond to directories on the host

- if Docker runs in a Linux VM, these directories are in the Linux VM

- When running on Docker Desktop:

- volumes correspond to directories in a small Linux VM running Docker

- access to bind mounts is translated to host filesystem access
 
 (a bit like a network filesystem)

.debug[[containers/Local_Development_Workflow.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Local_Development_Workflow.md)]
---

## Docker Desktop caveats

- When running Docker natively on Linux, accessing a mount = native I/O

- When running Docker Desktop, accessing a bind mount = file access translation

- That file access translation has relatively good performance *in general*

(watch out, however, for that big `npm install` working on a bind mount!)

- There are some corner cases when watching files (with mechanisms like inotify)

- Features like "live reload" or programs like `entr` don't always behave properly

(due to e.g. file attribute caching, and other interesting details!)

.debug[[containers/Local_Development_Workflow.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Local_Development_Workflow.md)]
---

## Trash your servers and burn your code

*(This is the title of a
[2013 blog post](http://chadfowler.com/2013/06/23/immutable-deployments.html)
by Chad Fowler, where he explains the concept of immutable infrastructure.)*

* Let's majorly mess up our container.

(Remove files or whatever.)

* Now, how can we fix this?

* Our old container (with the blue version of the code) is still running.

* See on which port it is exposed:
  ```bash
  docker ps
  ```

* Point our browser to it to confirm that it still works fine.

.debug[[containers/Local_Development_Workflow.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Local_Development_Workflow.md)]
---

## Immutable infrastructure in a nutshell

* Instead of *updating* a server, we deploy a new one.

* This might be challenging with classical servers, but it's trivial with containers.

* In fact, with Docker, the most logical workflow is to build a new image and run it.

* If something goes wrong with the new image, we can always restart the old one.

* We can even keep both versions running side by side.

If this pattern sounds interesting, you might want to read about *blue/green deployment*
and *canary deployments*.

.debug[[containers/Local_Development_Workflow.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Local_Development_Workflow.md)]
---

## Recap of the development workflow

1. Write a Dockerfile to build an image containing our development environment.
 
 (Rails, Django, ... and all the dependencies for our app)

2. Start a container from that image.
 
 Use the `-v` flag to mount our source code inside the container.

3. Edit the source code outside the container, using familiar tools.
 
 (vim, emacs, textmate...)

4. Test the application.
 
 (Some frameworks pick up changes automatically.
 Others require you to Ctrl-C + restart after each modification.)

5. Iterate and repeat steps 3 and 4 until satisfied.

6. When done, commit+push source code changes.

.debug[[containers/Local_Development_Workflow.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Local_Development_Workflow.md)]
---

## Debugging inside the container

Docker has a command called `docker exec`.

It allows users to run a new process in a container which is already running.

If sometimes you find yourself wishing you could SSH into a container: you can use `docker exec` instead.

You can get a shell prompt inside an existing container this way, or run an arbitrary process for automation.

.debug[[containers/Local_Development_Workflow.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Local_Development_Workflow.md)]
---

## `docker exec` example

```bash
$ # You can run ruby commands in the area the app is running and more!
$ docker exec -it <yourContainerId> bash
root@5ca27cf74c2e:/opt/namer# irb
irb(main):001:0> [0, 1, 2, 3, 4].map {|x| x ** 2}.compact
=> [0, 1, 4, 9, 16]
irb(main):002:0> exit
```

.debug[[containers/Local_Development_Workflow.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Local_Development_Workflow.md)]
---

## Stopping the container

Now that we're done let's stop our container.

```bash
$ docker stop <yourContainerID>
```

And remove it.

```bash
$ docker rm <yourContainerID>
```

.debug[[containers/Local_Development_Workflow.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Local_Development_Workflow.md)]
---

## Section summary

We've learned how to:

* Share code between container and host.

* Set our working directory.

* Use a simple local development workflow.

???

:EN:Developing with containers
:EN:- “Containerize” a development environment

:FR:Développer au jour le jour
:FR:- « Containeriser » son environnement de développement

.debug[[containers/Local_Development_Workflow.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Local_Development_Workflow.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/train-of-containers-1.jpg)]

---

The Container Network Model

.nav[
[Previous part](#toc-local-development-workflow-with-docker)
|
[Back to table of contents](#toc-part-2)
|
[Next part](#toc-service-discovery-with-containers)
]

---

# The Container Network Model

![A denser graph network](images/title-the-container-network-model.jpg)

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Objectives

We will learn about the CNM (Container Network Model).

At the end of this lesson, you will be able to:

* Create a private network for a group of containers.

* Use container naming to connect services together.

* Dynamically connect and disconnect containers to networks.

* Set the IP address of a container.

We will also explain the principle of overlay networks and network plugins.

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## The Container Network Model

Docker has "networks".

We can manage them with the `docker network` commands; for instance:

```bash
$ docker network ls
NETWORK ID          NAME                DRIVER
6bde79dfcf70        bridge              bridge
8d9c78725538        none                null
eb0eeab782f4        host                host
4c1ff84d6d3f        blog-dev            overlay
228a4355d548        blog-prod           overlay
```

New networks can be created (with `docker network create`).

(Note: networks `none` and `host` are special; let's set them aside for now.)

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## What's a network?

- Conceptually, a Docker "network" is a virtual switch

(we can also think about it like a VLAN, or a WiFi SSID, for instance)

- By default, containers are connected to a single network

(but they can be connected to zero, or many networks, even dynamically)

- Each network has its own subnet (IP address range)

- A network can be local (to a single Docker Engine) or global (span multiple hosts)

- Containers can have *network aliases* providing DNS-based service discovery

(and each network has its own "domain", "zone", or "scope")

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Service discovery

- A container can be given a network alias

(e.g. with `docker run --net some-network --net-alias db ...`)

- The containers running in the same network can resolve that network alias

(i.e. if they do a DNS lookup on `db`, it will give the container's address)

- We can have a different `db` container in each network

(this avoids naming conflicts between different stacks)

- When we name a container, it automatically adds the name as a network alias

(i.e. `docker run --name xyz ...` is like `docker run --net-alias xyz ...`

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Network isolation

- Networks are isolated

- By default, containers in network A cannot reach those in network B

- A container connected to both networks A and B can act as a router or proxy

- Published ports are always reachable through the Docker host address

(`docker run -P ...` makes a container port available to everyone)

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## How to use networks

- We typically create one network per "stack" or app that we deploy

- More complex apps or stacks might require multiple networks

(e.g. `frontend`, `backend`, ...)

- Networks allow us to deploy multiple copies of the same stack

(e.g. `prod`, `dev`, `pr-442`, ....)

- If we use Docker Compose, this is managed automatically for us

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

![Multiple containers on the default bridge network, on a Linux machine](images/docker-networking-default-bridge-linux.png)

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

![Multiple containers in multiple bridge networks, on a Linux machine](images/docker-networking-networks-linux.png)

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

![Multiple containers in multiple bridge networks, on a Mac/Windows machine](images/docker-networking-networks-macwin.png)

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## CNM vs CNI

- CNM is the model used by Docker

- Kubernetes uses a different model, architectured around CNI

(CNI is a kind of API between a container engine and *CNI plugins*)

- Docker model:

- multiple isolated networks
  - per-network service discovery
  - network interconnection requires extra steps

- Kubernetes model:

- single flat network
  - per-namespace service discovery
  - network isolation requires extra steps (Network Policies)

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Creating a network

Let's create a network called `dev`.

```bash
$ docker network create dev
4c1ff84d6d3f1733d3e233ee039cac276f425a9d5228a4355d54878293a889ba
```

The network is now visible with the `network ls` command:

```bash
$ docker network ls
NETWORK ID          NAME                DRIVER
6bde79dfcf70        bridge              bridge
8d9c78725538        none                null
eb0eeab782f4        host                host
4c1ff84d6d3f        dev                 bridge
```

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Placing containers on a network

We will create a *named* container on this network.

It will be reachable with its name, `es`.

```bash
$ docker run -d --name es --net dev elasticsearch:2
8abb80e229ce8926c7223beb69699f5f34d6f1d438bfc5682db893e798046863
```

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Communication between containers

Now, create another container on this network.

From this new container, we can resolve and ping the other one, using its assigned name:

.small[
```bash
/ # ping es
PING es (172.18.0.2) 56(84) bytes of data.
64 bytes from es.dev (172.18.0.2): icmp_seq=1 ttl=64 time=0.221 ms
64 bytes from es.dev (172.18.0.2): icmp_seq=2 ttl=64 time=0.114 ms
64 bytes from es.dev (172.18.0.2): icmp_seq=3 ttl=64 time=0.114 ms
^C
--- es ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2000ms
rtt min/avg/max/mdev = 0.114/0.149/0.221/0.052 ms
root@0ecccdfa45ef:/#
```
]

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Resolving container addresses

Since Docker Engine 1.10, name resolution is implemented by a dynamic resolver.

Archeological note: when CNM was intoduced (in Docker Engine 1.9, November 2015)
name resolution was implemented with `/etc/hosts`, and it was updated each time
CONTAINERs were added/removed. This could cause interesting race conditions
since `/etc/hosts` was a bind-mount (and couldn't be updated atomically).

.small[
```bash
[root@0ecccdfa45ef /]# cat /etc/hosts
172.18.0.3  0ecccdfa45ef
127.0.0.1       localhost
::1     localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
172.18.0.2      es
172.18.0.2      es.dev
```
]

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/train-of-containers-2.jpg)]

---

Service discovery with containers

.nav[
[Previous part](#toc-the-container-network-model)
|
[Back to table of contents](#toc-part-2)
|
[Next part](#toc-compose-for-development-stacks)
]

---

# Service discovery with containers

* Let's try to run an application that requires two containers.

* The first container is a web server.

* The other one is a redis data store.

* We will place them both on the `dev` network created before.

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Running the web server

* The application is provided by the container image `jpetazzo/trainingwheels`.

* We don't know much about it so we will try to run it and see what happens!

Start the container, exposing all its ports:

```bash
$ docker run --net dev -d -P jpetazzo/trainingwheels
```

Check the port that has been allocated to it:

```bash
$ docker ps -l
```

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Test the web server

* If we connect to the application now, we will see an error page:

![Trainingwheels error](images/trainingwheels-error.png)

* This is because the Redis service is not running.
* This container tries to resolve the name `redis`.

Note: we're not using a FQDN or an IP address here; just `redis`.

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Start the data store

* We need to start a Redis container.

* That container must be on the same network as the web server.

* It must have the right network alias (`redis`) so the application can find it.

Start the container:

```bash
$ docker run --net dev --net-alias redis -d redis
```

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Test the web server again

* If we connect to the application now, we should see that the app is working correctly:

![Trainingwheels OK](images/trainingwheels-ok.png)

* When the app tries to resolve `redis`, instead of getting a DNS error, it gets the IP address of our Redis container.

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## A few words on *scope*

- Container names are unique (there can be only one `--name redis`)

- Network aliases are not unique

- We can have the same network alias in different networks:
  ```bash
  docker run --net dev --net-alias redis ...
  docker run --net prod --net-alias redis ...
  ```

- We can even have multiple containers with the same alias in the same network

(in that case, we get multiple DNS entries, aka "DNS round robin")

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Names are *local* to each network

Let's try to ping our `es` container from another container, when that other container is *not* on the `dev` network.

```bash
$ docker run --rm alpine ping es
ping: bad address 'es'
```

Names can be resolved only when containers are on the same network.

Containers can contact each other only when they are on the same network (you can try to ping using the IP address to verify).

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Network aliases

We would like to have another network, `prod`, with its own `es` container. But there can be only one container named `es`!

We will use *network aliases*.

A container can have multiple network aliases.

Network aliases are *local* to a given network (only exist in this network).

Multiple containers can have the same network alias (even on the same network).

Since Docker Engine 1.11, resolving a network alias yields the IP addresses of all containers holding this alias.

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Creating containers on another network

Create the `prod` network.

```bash
$ docker network create prod
5a41562fecf2d8f115bedc16865f7336232a04268bdf2bd816aecca01b68d50c
```

We can now create multiple containers with the `es` alias on the new `prod` network.

```bash
$ docker run -d --name prod-es-1 --net-alias es --net prod elasticsearch:2
38079d21caf0c5533a391700d9e9e920724e89200083df73211081c8a356d771
$ docker run -d --name prod-es-2 --net-alias es --net prod elasticsearch:2
1820087a9c600f43159688050dcc164c298183e1d2e62d5694fd46b10ac3bc3d
```

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Resolving network aliases

Let's try DNS resolution first, using the `nslookup` tool that ships with the `alpine` image.

```bash
$ docker run --net prod --rm alpine nslookup es
Name:      es
Address 1: 172.23.0.3 prod-es-2.prod
Address 2: 172.23.0.2 prod-es-1.prod
```

(You can ignore the `can't resolve '(null)'` errors.)

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Connecting to aliased containers

Each ElasticSearch instance has a name (generated when it is started). This name can be seen when we issue a simple HTTP request on the ElasticSearch API endpoint.

Try the following command a few times:

Then try it a few times by replacing `--net dev` with `--net prod`:

.small[
```bash
$ docker run --rm --net prod centos curl -s es:9200
{
  "name" : "The Symbiote",
...
}
```
]

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Good to know ...

* Docker will not create network names and aliases on the default `bridge` network.

* Therefore, if you want to use those features, you have to create a custom network first.

* Network aliases are *not* unique on a given network.

* i.e., multiple containers can have the same alias on the same network.

* In that scenario, the Docker DNS server will return multiple records.
 
 (i.e. you will get DNS round robin out of the box.)

* Enabling *Swarm Mode* gives access to clustering and load balancing with IPVS.

* Creation of networks and network aliases is generally automated with tools like Compose.

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## A few words about round robin DNS

Don't rely exclusively on round robin DNS to achieve load balancing.

Many factors can affect DNS resolution, and you might see:

- all traffic going to a single instance;
- traffic being split (unevenly) between some instances;
- different behavior depending on your application language;
- different behavior depending on your base distro;
- different behavior depending on other factors (sic).

It's OK to use DNS to discover available endpoints, but remember that you have to re-resolve every now and then to discover new endpoints.

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Custom networks

When creating a network, extra options can be provided.

* `--internal` disables outbound traffic (the network won't have a default gateway).

* `--gateway` indicates which address to use for the gateway (when outbound traffic is allowed).

* `--subnet` (in CIDR notation) indicates the subnet to use.

* `--ip-range` (in CIDR notation) indicates the subnet to allocate from.

* `--aux-address` allows specifying a list of reserved addresses (which won't be allocated to containers).

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Setting containers' IP address

* It is possible to set a container's address with `--ip`.
* The IP address has to be within the subnet used for the container.

A full example would look like this.

```bash
$ docker network create --subnet 10.66.0.0/16 pubnet
42fb16ec412383db6289a3e39c3c0224f395d7f85bcb1859b279e7a564d4e135
$ docker run --net pubnet --ip 10.66.66.66 -d nginx
b2887adeb5578a01fd9c55c435cad56bbbe802350711d2743691f95743680b09
```

*Note: don't hard code container IP addresses in your code!*

*I repeat: don't hard code container IP addresses in your code!*

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Network drivers

* A network is managed by a *driver*.

* The built-in drivers include:

* `bridge` (default)
  * `none`
  * `host`
  * `macvlan`
  * `overlay` (for Swarm clusters)

* More drivers can be provided by plugins (OVS, VLAN...)

* A network can have a custom IPAM (IP allocator).

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Overlay networks

* The features we've seen so far only work when all containers are on a single host.

* If containers span multiple hosts, we need an *overlay* network to connect them together.

* Docker ships with a default network plugin, `overlay`, implementing an overlay network leveraging
  VXLAN, *enabled with Swarm Mode*.

* Other plugins (Weave, Calico...) can provide overlay networks as well.

* Once you have an overlay network, *all the features that we've used in this chapter work identically
  across multiple hosts.*

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Multi-host networking (overlay)

Out of the scope for this intro-level workshop!

Very short instructions:

- enable Swarm Mode (`docker swarm init` then `docker swarm join` on other nodes)
- `docker network create mynet --driver overlay`
- `docker service create --network mynet myimage`

If you want to learn more about Swarm mode, you can check
[this video](https://www.youtube.com/watch?v=EuzoEaE6Cqs)
or [these slides](https://container.training/swarm-selfpaced.yml.html).

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Multi-host networking (plugins)

Out of the scope for this intro-level workshop!

General idea:

- install the plugin (they often ship within containers)

- run the plugin (if it's in a container, it will often require extra parameters; don't just `docker run` it blindly!)

- some plugins require configuration or activation (creating a special file that tells Docker "use the plugin whose control socket is at the following location")

- you can then `docker network create --driver pluginname`

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Connecting and disconnecting dynamically

* So far, we have specified which network to use when starting the container.

* The Docker Engine also allows connecting and disconnecting while the container is running.

* This feature is exposed through the Docker API, and through two Docker CLI commands:

* `docker network connect <network> <container>`

* `docker network disconnect <network> <container>`

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Dynamically connecting to a network

* We have a container named `es` connected to a network named `dev`.

* Let's start a simple alpine container on the default network:

```bash
  $ docker run -ti alpine sh
  / #
  ```

* In this container, try to ping the `es` container:

```bash
  / # ping es
  ping: bad address 'es'
  ```

This doesn't work, but we will change that by connecting the container.

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Finding the container ID and connecting it

* Figure out the ID of our alpine container; here are two methods:

* looking at `/etc/hostname` in the container,

* running `docker ps -lq` on the host.

* Run the following command on the host:

```bash
 $ docker network connect dev `<container_id>`
 ```

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Checking what we did

* Try again to `ping es` from the container.

* It should now work correctly:

```bash
  / # ping es
  PING es (172.20.0.3): 56 data bytes
  64 bytes from 172.20.0.3: seq=0 ttl=64 time=0.376 ms
  64 bytes from 172.20.0.3: seq=1 ttl=64 time=0.130 ms
  ^C
  ```

* Interrupt it with Ctrl-C.

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Looking at the network setup in the container

We can look at the list of network interfaces with `ifconfig`, `ip a`, or `ip l`:

.small[
```bash
/ # ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN qlen 1000
 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
 inet 127.0.0.1/8 scope host lo
 valid_lft forever preferred_lft forever
18: eth0@if19: <BROADCAST,MULTICAST,UP,LOWER_UP,M-DOWN> mtu 1500 qdisc noqueue state UP
 link/ether 02:42:ac:11:00:02 brd ff:ff:ff:ff:ff:ff
 inet 172.17.0.2/16 brd 172.17.255.255 scope global eth0
 valid_lft forever preferred_lft forever
20: eth1@if21: <BROADCAST,MULTICAST,UP,LOWER_UP,M-DOWN> mtu 1500 qdisc noqueue state UP
 link/ether 02:42:ac:14:00:04 brd ff:ff:ff:ff:ff:ff
 inet 172.20.0.4/16 brd 172.20.255.255 scope global eth1
 valid_lft forever preferred_lft forever
/ #
```
]

Each network connection is materialized with a virtual network interface.

As we can see, we can be connected to multiple networks at the same time.

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Disconnecting from a network

* Let's try the symmetrical command to disconnect the container:
 ```bash
 $ docker network disconnect dev <container_id>
 ```

* From now on, if we try to ping `es`, it will not resolve:
  ```bash
  / # ping es
  ping: bad address 'es'
  ```

* Trying to ping the IP address directly won't work either:
  ```bash
  / # ping 172.20.0.3
  ... (nothing happens until we interrupt it with Ctrl-C)
  ```

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Network aliases are scoped per network

* Each network has its own set of network aliases.

* We saw this earlier: `es` resolves to different addresses in `dev` and `prod`.

* If we are connected to multiple networks, the resolver looks up names in each of them
  (as of Docker Engine 18.03, it is the connection order) and stops as soon as the name
  is found.

* Therefore, if we are connected to both `dev` and `prod`, resolving `es` will **not**
  give us the addresses of all the `es` services; but only the ones in `dev` or `prod`.

* However, we can lookup `es.dev` or `es.prod` if we need to.

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Finding out about our networks and names

* We can do reverse DNS lookups on containers' IP addresses.

* If the IP address belongs to a network (other than the default bridge), the result will be:

```
  name-or-first-alias-or-container-id.network-name
  ```

* Example:

.small[
```bash
$ docker run -ti --net prod --net-alias hello alpine
/ # apk add --no-cache drill
...
OK: 5 MiB in 13 packages
/ # ifconfig
eth0      Link encap:Ethernet  HWaddr 02:42:AC:15:00:03
          inet addr:`172.21.0.3`  Bcast:172.21.255.255  Mask:255.255.0.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
...
/ # drill -t ptr `3.0.21.172`.in-addr.arpa
...
;; ANSWER SECTION:
3.0.21.172.in-addr.arpa.	600	IN	PTR	`hello.prod`.
...
```
]

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

## Building with a custom network

* We can build a Dockerfile with a custom network with `docker build --network NAME`.

* This can be used to check that a build doesn't access the network.

(But keep in mind that most Dockerfiles will fail,
 because they need to install remote packages and dependencies!)

* This may be used to access an internal package repository.

(But try to use a multi-stage build instead, if possible!)

???

:EN:Container networking essentials
:EN:- The Container Network Model
:EN:- Container isolation
:EN:- Service discovery

:FR:Mettre ses conteneurs en réseau
:FR:- Le "Container Network Model"
:FR:- Isolation des conteneurs
:FR:- *Service discovery*

.debug[[containers/Container_Network_Model.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Container_Network_Model.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/two-containers-on-a-truck.jpg)]

---

Compose for development stacks

.nav[
[Previous part](#toc-service-discovery-with-containers)
|
[Back to table of contents](#toc-part-2)
|
[Next part](#toc-exercise--writing-a-compose-file)
]

---
# Compose for development stacks

Dockerfile = great to build *one* container image.

What if we have multiple containers?

What if some of them require particular `docker run` parameters?

How do we connect them all together?

... Compose solves these use-cases (and a few more).

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

## Life before Compose

Before we had Compose, we would typically write custom scripts to:

- build container images,

- run containers using these images,

- connect the containers together,

- rebuild, restart, update these images and containers.

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

## Life with Compose

Compose enables a simple, powerful onboarding workflow:

1. Checkout our code.

2. Run `docker-compose up`.

3. Our app is up and running!

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

![composeup](images/composeup.gif)

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

## Life after Compose

(Or: when do we need something else?)

- Compose is *not* an orchestrator

- It isn't designed to need to run containers on multiple nodes

(it can, however, work with Docker Swarm Mode)

- Compose isn't ideal if we want to run containers on Kubernetes

- it uses different concepts (Compose services ≠ Kubernetes services)

- it needs a Docker Engine (althought containerd support might be coming)

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

## First rodeo with Compose

1. Write Dockerfiles

2. Describe our stack of containers in a YAML file called `docker-compose.yml`

3. `docker-compose up` (or `docker-compose up -d` to run in the background)

4. Compose pulls and builds the required images, and starts the containers

5. Compose shows the combined logs of all the containers

(if running in the background, use `docker-compose logs`)

6. Hit Ctrl-C to stop the whole stack

(if running in the background, use `docker-compose stop`)

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

## Iterating

After making changes to our source code, we can:

1. `docker-compose build` to rebuild container images

2. `docker-compose up` to restart the stack with the new images

We can also combine both with `docker-compose up --build`

Compose will be smart, and only recreate the containers that have changed.

When working with interpreted languages:

- don't rebuild each time

- leverage a `volumes` section instead

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

## Launching Our First Stack with Compose

First step: clone the source code for the app we will be working on.

```bash
git clone https://github.com/jpetazzo/trainingwheels
cd trainingwheels
```

Second step: start the app.

```bash
docker-compose up
```

Watch Compose build and run the app.

That Compose stack exposes a web server on port 8000; try connecting to it.

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

## Launching Our First Stack with Compose

We should see a web page like this:

![composeapp](images/composeapp.png)

Each time we reload, the counter should increase.

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

## Stopping the app

When we hit Ctrl-C, Compose tries to gracefully terminate all of the containers.

After ten seconds (or if we press `^C` again) it will forcibly kill them.

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

## The `docker-compose.yml` file

Here is the file used in the demo:

services:
  www:
    build: www
    ports:
      - ${PORT-8000}:5000
    user: nobody
    environment:
      DEBUG: 1
    command: python counter.py
    volumes:
      - ./www:/src

redis:
    image: redis
```
]

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

## Compose file structure

A Compose file has multiple sections:

* `version` is mandatory. (Typically use "3".)

* `services` is mandatory. Each service corresponds to a container.

* `networks` is optional and indicates to which networks containers should be connected.
 (By default, containers will be connected on a private, per-compose-file network.)

* `volumes` is optional and can define volumes to be used and/or shared by the containers.

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

## Compose file versions

* Version 1 is legacy and shouldn't be used.

(If you see a Compose file without `version` and `services`, it's a legacy v1 file.)

* Version 2 added support for networks and volumes.

* Version 3 added support for deployment options (scaling, rolling updates, etc).

* Typically use `version: "3"`.

The [Docker documentation](https://docs.docker.com/compose/compose-file/)
has excellent information about the Compose file format if you need to know more about versions.

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

## Containers in `docker-compose.yml`

Each service in the YAML file must contain either `build`, or `image`.

* `build` indicates a path containing a Dockerfile.

* `image` indicates an image name (local, or on a registry).

* If both are specified, an image will be built from the `build` directory and named `image`.

The other parameters are optional.

They encode the parameters that you would typically add to `docker run`.

Sometimes they have several minor improvements.

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

## Container parameters

* `command` indicates what to run (like `CMD` in a Dockerfile).

* `ports` translates to one (or multiple) `-p` options to map ports.
 You can specify local ports (i.e. `x:y` to expose public port `x`).

* `volumes` translates to one (or multiple) `-v` options.
 You can use relative paths here.

For the full list, check: https://docs.docker.com/compose/compose-file/

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

## Environment variables

- We can use environment variables in Compose files

(like `$THIS` or `${THAT}`)

- We can provide default values, e.g. `${PORT-8000}`

- Compose will also automatically load the environment file `.env`

(it should contain `VAR=value`, one per line)

- This is a great way to customize build and run parameters

(base image versions to use, build and run secrets, port numbers...)

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

## Configuring a Compose stack

- Follow [12-factor app configuration principles][12factorconfig]

(configure the app through environment variables)

- Provide (in the repo) a default environment file suitable for development

(no secret or sensitive value)

- Copy the default environment file to `.env` and tweak it

(or: provide a script to generate `.env` from a template)

[12factorconfig]: https://12factor.net/config

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

## Running multiple copies of a stack

- Copy the stack in two different directories, e.g. `front` and `frontcopy`

- Compose prefixes images and containers with the directory name:

`front_www`, `front_www_1`, `front_db_1`

`frontcopy_www`, `frontcopy_www_1`, `frontcopy_db_1`

- Alternatively, use `docker-compose -p frontcopy`

(to set the `--project-name` of a stack, which default to the dir name)

- Each copy is isolated from the others (runs on a different network)

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

## Checking stack status

We have `ps`, `docker ps`, and similarly, `docker-compose ps`:

```bash
$ docker-compose ps
Name                      Command             State           Ports          
----------------------------------------------------------------------------
trainingwheels_redis_1   /entrypoint.sh red   Up      6379/tcp               
trainingwheels_www_1     python counter.py    Up      0.0.0.0:8000->5000/tcp 
```

Shows the status of all the containers of our stack.

Doesn't show the other containers.

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

## Cleaning up (1)

If you have started your application in the background with Compose and
want to stop it easily, you can use the `kill` command:

```bash
$ docker-compose kill
```

Likewise, `docker-compose rm` will let you remove containers (after confirmation):

```bash
$ docker-compose rm
Going to remove trainingwheels_redis_1, trainingwheels_www_1
Are you sure? [yN] y
Removing trainingwheels_redis_1...
Removing trainingwheels_www_1...
```

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

## Cleaning up (2)

Alternatively, `docker-compose down` will stop and remove containers.

It will also remove other resources, like networks that were created for the application.

```bash
$ docker-compose down
Stopping trainingwheels_www_1 ... done
Stopping trainingwheels_redis_1 ... done
Removing trainingwheels_www_1 ... done
Removing trainingwheels_redis_1 ... done
```

Use `docker-compose down -v` to remove everything including volumes.

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

## Special handling of volumes

- When an image gets updated, Compose automatically creates a new container

- The data in the old container is lost...

- ...Except if the container is using a *volume*

- Compose will then re-attach that volume to the new container

(and data is then retained across database upgrades)

- All good database images use volumes

(e.g. all official images)

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

## Gotchas with volumes

- Unfortunately, Docker volumes don't have labels or metadata

- Compose tracks volumes thanks to their associated container

- If the container is deleted, the volume gets orphaned

- Example: `docker-compose down && docker-compose up`

- the old volume still exists, detached from its container

- a new volume gets created

- `docker-compose down -v`/`--volumes` deletes volumes

(but **not** `docker-compose down && docker-compose down -v`!)
 
.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

## Managing volumes explicitly

Option 1: *named volumes*

```yaml
services:
  app:
    volumes:
    - data:/some/path
volumes:
  data:
```

- Volume will be named `<project>_data`

- It won't be orphaned with `docker-compose down`

- It will correctly be removed with `docker-compose down -v`

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

## Managing volumes explicitly

Option 2: *relative paths*

```yaml
services:
  app:
    volumes:
    - ./data:/some/path
```

- Makes it easy to colocate the app and its data

(for migration, backups, disk usage accounting...)

- Won't be removed by `docker-compose down -v`

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

## Managing complex stacks

- Compose provides multiple features to manage complex stacks

(with many containers)

- `-f`/`--file`/`$COMPOSE_FILE` can be a list of Compose files

(separated by `:` and merged together)

- Services can be assigned to one or more *profiles*

- `--profile`/`$COMPOSE_PROFILE` can be a list of comma-separated profiles

(see [Using service profiles][profiles] in the Compose documentation)

- These variables can be set in `.env`

[profiles]: https://docs.docker.com/compose/profiles/

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

## Dependencies

- A service can have a `depends_on` section

(listing one or more other services)

- This is used when bringing up individual services

(e.g. `docker-compose up blah` or `docker-compose run foo`)

⚠️ It doesn't make a service "wait" for another one to be up!

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

## A bit of history and trivia

- Compose was initially named "Fig"

- Compose is one of the only components of Docker written in Python

(almost everything else is in Go)

- In 2020, Docker introduced "Compose CLI":

- `docker compose` command to deploy Compose stacks to some clouds

- progressively getting feature parity with `docker-compose`

- also provides numerous improvements (e.g. leverages BuildKit by default)

???

:EN:- Using compose to describe an environment
:EN:- Connecting services together with a *Compose file*

:FR:- Utiliser Compose pour décrire son environnement
:FR:- Écrire un *Compose file* pour connecter les services entre eux

.debug[[containers/Compose_For_Dev_Stacks.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Compose_For_Dev_Stacks.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/wall-of-containers.jpeg)]

---

Exercise — writing a Compose file

.nav[
[Previous part](#toc-compose-for-development-stacks)
|
[Back to table of contents](#toc-part-2)
|
[Next part](#toc-restarting-and-attaching-to-containers)
]

---
# Exercise — writing a Compose file

Let's write a Compose file for the wordsmith app!

The code is at: https://github.com/jpetazzo/wordsmith

.debug[[containers/Exercise_Composefile.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Exercise_Composefile.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/Container-Ship-Freighter-Navigation-Elbe-Romance-1782991.jpg)]

---

Restarting and attaching to containers

.nav[
[Previous part](#toc-exercise--writing-a-compose-file)
|
[Back to table of contents](#toc-part-3)
|
[Next part](#toc-naming-and-inspecting-containers)
]

---
# Restarting and attaching to containers

We have started containers in the foreground, and in the background.

In this chapter, we will see how to:

* Put a container in the background.
* Attach to a background container to bring it to the foreground.
* Restart a stopped container.

.debug[[containers/Start_And_Attach.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Start_And_Attach.md)]
---

## Background and foreground

The distinction between foreground and background containers is arbitrary.

From Docker's point of view, all containers are the same.

All containers run the same way, whether there is a client attached to them or not.

It is always possible to detach from a container, and to reattach to a container.

Analogy: attaching to a container is like plugging a keyboard and screen to a physical server.

.debug[[containers/Start_And_Attach.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Start_And_Attach.md)]
---

## Detaching from a container (Linux/macOS)

* If you have started an *interactive* container (with option `-it`), you can detach from it.

* The "detach" sequence is `^P^Q`.

* Otherwise you can detach by killing the Docker client.
  
  (But not by hitting `^C`, as this would deliver `SIGINT` to the container.)

What does `-it` stand for?

* `-t` means "allocate a terminal."
* `-i` means "connect stdin to the terminal."

.debug[[containers/Start_And_Attach.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Start_And_Attach.md)]
---

## Detaching cont. (Win PowerShell and cmd.exe)

* Docker for Windows has a different detach experience due to shell features.

* `^P^Q` does not work.

* `^C` will detach, rather than stop the container.

* Using Bash, Subsystem for Linux, etc. on Windows behaves like Linux/macOS shells.

* Both PowerShell and Bash work well in Win 10; just be aware of differences.

.debug[[containers/Start_And_Attach.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Start_And_Attach.md)]
---

## Specifying a custom detach sequence

* You don't like `^P^Q`? No problem!
* You can change the sequence with `docker run --detach-keys`.
* This can also be passed as a global option to the engine.

Start a container with a custom detach command:

```bash
$ docker run -ti --detach-keys ctrl-x,x jpetazzo/clock
```

Detach by hitting `^X x`. (This is ctrl-x then x, not ctrl-x twice!)

Check that our container is still running:

```bash
$ docker ps -l
```

.debug[[containers/Start_And_Attach.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Start_And_Attach.md)]
---

## Attaching to a container

You can attach to a container:

```bash
$ docker attach <containerID>
```

* The container must be running.
* There *can* be multiple clients attached to the same container.
* If you don't specify `--detach-keys` when attaching, it defaults back to `^P^Q`.

Try it on our previous container:

```bash
$ docker attach $(docker ps -lq)
```

Check that `^X x` doesn't work, but `^P ^Q` does.

.debug[[containers/Start_And_Attach.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Start_And_Attach.md)]
---

## Detaching from non-interactive containers

* **Warning:** if the container was started without `-it`...

* You won't be able to detach with `^P^Q`.
  * If you hit `^C`, the signal will be proxied to the container.

* Remember: you can always detach by killing the Docker client.

.debug[[containers/Start_And_Attach.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Start_And_Attach.md)]
---

## Checking container output

* Use `docker attach` if you intend to send input to the container.

* If you just want to see the output of a container, use `docker logs`.

```bash
$ docker logs --tail 1 --follow <containerID>
```

.debug[[containers/Start_And_Attach.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Start_And_Attach.md)]
---

## Restarting a container

When a container has exited, it is in stopped state.

It can then be restarted with the `start` command.

```bash
$ docker start <yourContainerID>
```

The container will be restarted using the same options you launched it
with.

You can re-attach to it if you want to interact with it:

```bash
$ docker attach <yourContainerID>
```

Use `docker ps -a` to identify the container ID of a previous `jpetazzo/clock` container,
and try those commands.

.debug[[containers/Start_And_Attach.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Start_And_Attach.md)]
---

## Attaching to a REPL

* REPL = Read Eval Print Loop

* Shells, interpreters, TUI ...

* Symptom: you `docker attach`, and see nothing

* The REPL doesn't know that you just attached, and doesn't print anything

* Try hitting `^L` or `Enter`

.debug[[containers/Start_And_Attach.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Start_And_Attach.md)]
---

## SIGWINCH

* When you `docker attach`, the Docker Engine sends SIGWINCH signals to the container.

* SIGWINCH = WINdow CHange; indicates a change in window size.

* This will cause some CLI and TUI programs to redraw the screen.

* But not all of them.

???

:EN:- Restarting old containers
:EN:- Detaching and reattaching to container
:FR:- Redémarrer des anciens conteneurs
:FR:- Se détacher et rattacher à des conteneurs

.debug[[containers/Start_And_Attach.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Start_And_Attach.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/ShippingContainerSFBay.jpg)]

---

Naming and inspecting containers

.nav[
[Previous part](#toc-restarting-and-attaching-to-containers)
|
[Back to table of contents](#toc-part-3)
|
[Next part](#toc-labels)
]

---

# Naming and inspecting containers

![Markings on container door](images/title-naming-and-inspecting-containers.jpg)

.debug[[containers/Naming_And_Inspecting.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Naming_And_Inspecting.md)]
---

## Objectives

In this lesson, we will learn about an important
Docker concept: container *naming*.

Naming allows us to:

* Reference easily a container.

* Ensure unicity of a specific container.

We will also see the `inspect` command, which gives a lot of details about a container.

.debug[[containers/Naming_And_Inspecting.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Naming_And_Inspecting.md)]
---

## Naming our containers

So far, we have referenced containers with their ID.

We have copy-pasted the ID, or used a shortened prefix.

But each container can also be referenced by its name.

If a container is named `thumbnail-worker`, I can do:

```bash
$ docker logs thumbnail-worker
$ docker stop thumbnail-worker
etc.
```

.debug[[containers/Naming_And_Inspecting.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Naming_And_Inspecting.md)]
---

## Default names

When we create a container, if we don't give a specific
name, Docker will pick one for us.

It will be the concatenation of:

* A mood (furious, goofy, suspicious, boring...)

* The name of a famous inventor (tesla, darwin, wozniak...)

Examples: `happy_curie`, `clever_hopper`, `jovial_lovelace` ...

.debug[[containers/Naming_And_Inspecting.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Naming_And_Inspecting.md)]
---

## Specifying a name

You can set the name of the container when you create it.

```bash
$ docker run --name ticktock jpetazzo/clock
```

If you specify a name that already exists, Docker will refuse
to create the container.

This lets us enforce unicity of a given resource.

.debug[[containers/Naming_And_Inspecting.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Naming_And_Inspecting.md)]
---

## Renaming containers

* You can rename containers with `docker rename`.

* This allows you to "free up" a name without destroying the associated container.

.debug[[containers/Naming_And_Inspecting.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Naming_And_Inspecting.md)]
---

## Inspecting a container

The `docker inspect` command will output a very detailed JSON map.

```bash
$ docker inspect <containerID>
[{
...
(many pages of JSON here)
...
```

There are multiple ways to consume that information.

.debug[[containers/Naming_And_Inspecting.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Naming_And_Inspecting.md)]
---

## Parsing JSON with the Shell

* You *could* grep and cut or awk the output of `docker inspect`.

* Please, don't.

* It's painful.

* If you really must parse JSON from the Shell, use JQ! (It's great.)

```bash
$ docker inspect <containerID> | jq .
```

* We will see a better solution which doesn't require extra tools.

.debug[[containers/Naming_And_Inspecting.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Naming_And_Inspecting.md)]
---

## Using `--format`

You can specify a format string, which will be parsed by 
Go's text/template package.

```bash
$ docker inspect --format '{{ json .Created }}' <containerID>
"2015-02-24T07:21:11.712240394Z"
```

* The generic syntax is to wrap the expression with double curly braces.

* The expression starts with a dot representing the JSON object.

* Then each field or member can be accessed in dotted notation syntax.

* The optional `json` keyword asks for valid JSON output.
 (e.g. here it adds the surrounding double-quotes.)

???

:EN:Managing container lifecycle
:EN:- Naming and inspecting containers

:FR:Suivre ses conteneurs à la loupe
:FR:- Obtenir des informations détaillées sur un conteneur
:FR:- Associer un identifiant unique à un conteneur

.debug[[containers/Naming_And_Inspecting.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Naming_And_Inspecting.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/aerial-view-of-containers.jpg)]

---

Labels

.nav[
[Previous part](#toc-naming-and-inspecting-containers)
|
[Back to table of contents](#toc-part-3)
|
[Next part](#toc-getting-inside-a-container)
]

---
# Labels

* Labels allow to attach arbitrary metadata to containers.

* Labels are key/value pairs.

* They are specified at container creation.

* You can query them with `docker inspect`.

* They can also be used as filters with some commands (e.g. `docker ps`).

.debug[[containers/Labels.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Labels.md)]
---

## Using labels

Let's create a few containers with a label `owner`.

```bash
docker run -d -l owner=alice nginx
docker run -d -l owner=bob nginx
docker run -d -l owner nginx
```

We didn't specify a value for the `owner` label in the last example.

This is equivalent to setting the value to be an empty string.

.debug[[containers/Labels.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Labels.md)]
---

## Querying labels

We can view the labels with `docker inspect`.

```bash
$ docker inspect $(docker ps -lq) | grep -A3 Labels
 "Labels": {
 "maintainer": "NGINX Docker Maintainers <docker-maint@nginx.com>",
 "owner": ""
 },
```

We can use the `--format` flag to list the value of a label.

```bash
$ docker inspect $(docker ps -q) --format 'OWNER={{.Config.Labels.owner}}'
```

.debug[[containers/Labels.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Labels.md)]
---

## Using labels to select containers

We can list containers having a specific label.

```bash
$ docker ps --filter label=owner
```

Or we can list containers having a specific label with a specific value.

```bash
$ docker ps --filter label=owner=alice
```

.debug[[containers/Labels.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Labels.md)]
---

## Use-cases for labels

* HTTP vhost of a web app or web service.

(The label is used to generate the configuration for NGINX, HAProxy, etc.)

* Backup schedule for a stateful service.

(The label is used by a cron job to determine if/when to backup container data.)

* Service ownership.

(To determine internal cross-billing, or who to page in case of outage.)

* etc.

???

:EN:- Using labels to identify containers
:FR:- Étiqueter ses conteneurs avec des méta-données

.debug[[containers/Labels.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Labels.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/blue-containers.jpg)]

---

Getting inside a container

.nav[
[Previous part](#toc-labels)
|
[Back to table of contents](#toc-part-3)
|
[Next part](#toc-tips-for-efficient-dockerfiles)
]

---

# Getting inside a container

![Person standing inside a container](images/getting-inside.png)

.debug[[containers/Getting_Inside.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Getting_Inside.md)]
---

## Objectives

On a traditional server or VM, we sometimes need to:

* log into the machine (with SSH or on the console),

* analyze the disks (by removing them or rebooting with a rescue system).

In this chapter, we will see how to do that with containers.

.debug[[containers/Getting_Inside.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Getting_Inside.md)]
---

## Getting a shell

Every once in a while, we want to log into a machine.

In an perfect world, this shouldn't be necessary.

* You need to install or update packages (and their configuration)?

Use configuration management. (e.g. Ansible, Chef, Puppet, Salt...)

* You need to view logs and metrics?

Collect and access them through a centralized platform.

In the real world, though ... we often need shell access!

.debug[[containers/Getting_Inside.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Getting_Inside.md)]
---

## Not getting a shell

Even without a perfect deployment system, we can do many operations without getting a shell.

* Installing packages can (and should) be done in the container image.

* Configuration can be done at the image level, or when the container starts.

* Dynamic configuration can be stored in a volume (shared with another container).

* Logs written to stdout are automatically collected by the Docker Engine.

* Other logs can be written to a shared volume.

* Process information and metrics are visible from the host.

_Let's save logging, volumes ... for later, but let's have a look at process information!_

.debug[[containers/Getting_Inside.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Getting_Inside.md)]
---

## Viewing container processes from the host

If you run Docker on Linux, container processes are visible on the host.

```bash
$ ps faux | less
```

* Scroll around the output of this command.

* You should see the `jpetazzo/clock` container.

* A containerized process is just like any other process on the host.

* We can use tools like `lsof`, `strace`, `gdb` ... To analyze them.

.debug[[containers/Getting_Inside.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Getting_Inside.md)]
---

## What's the difference between a container process and a host process?

* Each process (containerized or not) belongs to *namespaces* and *cgroups*.

* The namespaces and cgroups determine what a process can "see" and "do".

* Analogy: each process (containerized or not) runs with a specific UID (user ID).

* UID=0 is root, and has elevated privileges. Other UIDs are normal users.

_We will give more details about namespaces and cgroups later._

.debug[[containers/Getting_Inside.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Getting_Inside.md)]
---

## Getting a shell in a running container

* Sometimes, we need to get a shell anyway.

* We _could_ run some SSH server in the container ...

* But it is easier to use `docker exec`.

```bash
$ docker exec -ti ticktock sh
```

* This creates a new process (running `sh`) _inside_ the container.

* This can also be done "manually" with the tool `nsenter`.

.debug[[containers/Getting_Inside.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Getting_Inside.md)]
---

## Caveats

* The tool that you want to run needs to exist in the container.

* Some tools (like `ip netns exec`) let you attach to _one_ namespace at a time.

(This lets you e.g. setup network interfaces, even if you don't have `ifconfig` or `ip` in the container.)

* Most importantly: the container needs to be running.

* What if the container is stopped or crashed?

.debug[[containers/Getting_Inside.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Getting_Inside.md)]
---

## Getting a shell in a stopped container

* A stopped container is only _storage_ (like a disk drive).

* We cannot SSH into a disk drive or USB stick!

* We need to connect the disk to a running machine.

* How does that translate into the container world?

.debug[[containers/Getting_Inside.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Getting_Inside.md)]
---

## Analyzing a stopped container

As an exercise, we are going to try to find out what's wrong with `jpetazzo/crashtest`.

```bash
docker run jpetazzo/crashtest
```

The container starts, but then stops immediately, without any output.

What would MacGyver™ do?

First, let's check the status of that container.

```bash
docker ps -l
```

.debug[[containers/Getting_Inside.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Getting_Inside.md)]
---

## Viewing filesystem changes

* We can use `docker diff` to see files that were added / changed / removed.

```bash
docker diff <container_id>
```

* The container ID was shown by `docker ps -l`.

* We can also see it with `docker ps -lq`.

* The output of `docker diff` shows some interesting log files!

.debug[[containers/Getting_Inside.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Getting_Inside.md)]
---

## Accessing files

* We can extract files with `docker cp`.

```bash
docker cp <container_id>:/var/log/nginx/error.log .
```

* Then we can look at that log file.

```bash
cat error.log
```

(The directory `/run/nginx` doesn't exist.)

.debug[[containers/Getting_Inside.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Getting_Inside.md)]
---

## Exploring a crashed container

* We can restart a container with `docker start` ...

* ... But it will probably crash again immediately!

* We cannot specify a different program to run with `docker start`

* But we can create a new image from the crashed container

```bash
docker commit <container_id> debugimage
```

* Then we can run a new container from that image, with a custom entrypoint

```bash
docker run -ti --entrypoint sh debugimage
```

.debug[[containers/Getting_Inside.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Getting_Inside.md)]
---

## Obtaining a complete dump

* We can also dump the entire filesystem of a container.

* This is done with `docker export`.

* It generates a tar archive.

```bash
docker export <container_id> | tar tv
```

This will give a detailed listing of the content of the container.

???

:EN:- Troubleshooting and getting inside a container
:FR:- Inspecter un conteneur en détail, en *live* ou *post-mortem*

.debug[[containers/Getting_Inside.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Getting_Inside.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/chinook-helicopter-container.jpg)]

---

Tips for efficient Dockerfiles

.nav[
[Previous part](#toc-getting-inside-a-container)
|
[Back to table of contents](#toc-part-3)
|
[Next part](#toc-dockerfile-examples)
]

---
# Tips for efficient Dockerfiles

We will see how to:

* Reduce the number of layers.

* Leverage the build cache so that builds can be faster.

* Embed unit testing in the build process.

.debug[[containers/Dockerfile_Tips.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Dockerfile_Tips.md)]
---

## Reducing the number of layers

* Each line in a `Dockerfile` creates a new layer.

* Build your `Dockerfile` to take advantage of Docker's caching system.

* Combine commands by using `&&` to continue commands and `\` to wrap lines.

Note: it is frequent to build a Dockerfile line by line:

```dockerfile
RUN apt-get install thisthing
RUN apt-get install andthatthing andthatotherone
RUN apt-get install somemorestuff
```

And then refactor it trivially before shipping:

```dockerfile
RUN apt-get install thisthing andthatthing andthatotherone somemorestuff
```

.debug[[containers/Dockerfile_Tips.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Dockerfile_Tips.md)]
---

## Avoid re-installing dependencies at each build

* Classic Dockerfile problem:

"each time I change a line of code, all my dependencies are re-installed!"

* Solution: `COPY` dependency lists (`package.json`, `requirements.txt`, etc.)
  by themselves to avoid reinstalling unchanged dependencies every time.

.debug[[containers/Dockerfile_Tips.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Dockerfile_Tips.md)]
---

## Example "bad" `Dockerfile`

The dependencies are reinstalled every time, because the build system does not know if `requirements.txt` has been updated.

```bash
FROM python
WORKDIR /src
COPY . .
RUN pip install -qr requirements.txt
EXPOSE 5000
CMD ["python", "app.py"]
```

.debug[[containers/Dockerfile_Tips.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Dockerfile_Tips.md)]
---

## Fixed `Dockerfile`

Adding the dependencies as a separate step means that Docker can cache more efficiently and only install them when `requirements.txt` changes.

```bash
FROM python
WORKDIR /src
COPY requirements.txt .
RUN pip install -qr requirements.txt
COPY . .
EXPOSE 5000
CMD ["python", "app.py"]
```

.debug[[containers/Dockerfile_Tips.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Dockerfile_Tips.md)]
---

## Be careful with `chown`, `chmod`, `mv`

* Layers cannot store efficiently changes in permissions or ownership.

* Layers cannot represent efficiently when a file is moved either.

* As a result, operations like `chown`, `chown`, `mv` can be expensive.

* For instance, in the Dockerfile snippet below, each `RUN` line
  creates a layer with an entire copy of `some-file`.

```dockerfile
  COPY some-file .
  RUN chown www-data:www-data some-file
  RUN chmod 644 some-file
  RUN mv some-file /var/www
  ```

* How can we avoid that?

.debug[[containers/Dockerfile_Tips.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Dockerfile_Tips.md)]
---

## Put files on the right place

* Instead of using `mv`, directly put files at the right place.

* When extracting archives (tar, zip...), merge operations in a single layer.

Example:

```dockerfile
    ...
    RUN wget http://.../foo.tar.gz \
     && tar -zxf foo.tar.gz \
     && mv foo/fooctl /usr/local/bin \
     && rm -rf foo
  ...
  ```

.debug[[containers/Dockerfile_Tips.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Dockerfile_Tips.md)]
---

## Use `COPY --chown`

* The Dockerfile instruction `COPY` can take a `--chown` parameter.

Examples:

```dockerfile
  ...
  COPY --chown=1000 some-file .
  COPY --chown=1000:1000 some-file .
  COPY --chown=www-data:www-data some-file .
  ```

* The `--chown` flag can specify a user, or a user:group pair.

* The user and group can be specified as names or numbers.

* When using names, the names must exist in `/etc/passwd` or `/etc/group`.

*(In the container, not on the host!)*

.debug[[containers/Dockerfile_Tips.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Dockerfile_Tips.md)]
---

## Set correct permissions locally

* Instead of using `chmod`, set the right file permissions locally.

* When files are copied with `COPY`, permissions are preserved.

.debug[[containers/Dockerfile_Tips.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Dockerfile_Tips.md)]
---

## Embedding unit tests in the build process

```dockerfile
FROM <baseimage>
RUN <install dependencies>
COPY <code>
RUN <build code>
RUN <install test dependencies>
COPY <test data sets and fixtures>
RUN <unit tests>
FROM <baseimage>
RUN <install dependencies>
COPY <code>
RUN <build code>
CMD, EXPOSE ...
```

* The build fails as soon as an instruction fails
* If `RUN <unit tests>` fails, the build doesn't produce an image
* If it succeeds, it produces a clean image (without test libraries and data)

.debug[[containers/Dockerfile_Tips.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Dockerfile_Tips.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/container-cranes.jpg)]

---

Dockerfile examples

.nav[
[Previous part](#toc-tips-for-efficient-dockerfiles)
|
[Back to table of contents](#toc-part-3)
|
[Next part](#toc-advanced-dockerfile-syntax)
]

---

# Dockerfile examples

There are a number of tips, tricks, and techniques that we can use in Dockerfiles.

But sometimes, we have to use different (and even opposed) practices depending on:

- the complexity of our project,

- the programming language or framework that we are using,

- the stage of our project (early MVP vs. super-stable production),

- whether we're building a final image or a base for further images,

- etc.

We are going to show a few examples using very different techniques.

.debug[[containers/Dockerfile_Tips.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Dockerfile_Tips.md)]
---

## When to optimize an image

When authoring official images, it is a good idea to reduce as much as possible:

- the number of layers,

- the size of the final image.

This is often done at the expense of build time and convenience for the image maintainer;
but when an image is downloaded millions of time, saving even a few seconds of pull time
can be worth it.

.small[
```dockerfile
RUN apt-get update && apt-get install -y libpng12-dev libjpeg-dev && rm -rf /var/lib/apt/lists/* \
	&& docker-php-ext-configure gd --with-png-dir=/usr --with-jpeg-dir=/usr \
	&& docker-php-ext-install gd
...
RUN curl -o wordpress.tar.gz -SL https://wordpress.org/wordpress-${WORDPRESS_UPSTREAM_VERSION}.tar.gz \
	&& echo "$WORDPRESS_SHA1 *wordpress.tar.gz" | sha1sum -c - \
	&& tar -xzf wordpress.tar.gz -C /usr/src/ \
	&& rm wordpress.tar.gz \
	&& chown -R www-data:www-data /usr/src/wordpress
```
]

(Source: [Wordpress official image](https://github.com/docker-library/wordpress/blob/618490d4bdff6c5774b84b717979bfe3d6ba8ad1/apache/Dockerfile))

.debug[[containers/Dockerfile_Tips.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Dockerfile_Tips.md)]
---

## When to *not* optimize an image

Sometimes, it is better to prioritize *maintainer convenience*.

In particular, if:

- the image changes a lot,

- the image has very few users (e.g. only 1, the maintainer!),

- the image is built and run on the same machine,

- the image is built and run on machines with a very fast link ...

In these cases, just keep things simple!

(Next slide: a Dockerfile that can be used to preview a Jekyll / github pages site.)

.debug[[containers/Dockerfile_Tips.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Dockerfile_Tips.md)]
---

```dockerfile
FROM debian:sid

RUN apt-get update -q
RUN apt-get install -yq build-essential make
RUN apt-get install -yq zlib1g-dev
RUN apt-get install -yq ruby ruby-dev
RUN apt-get install -yq python-pygments
RUN apt-get install -yq nodejs
RUN apt-get install -yq cmake
RUN gem install --no-rdoc --no-ri github-pages

COPY . /blog
WORKDIR /blog

VOLUME /blog/_site

EXPOSE 4000
CMD ["jekyll", "serve", "--host", "0.0.0.0", "--incremental"]
```

.debug[[containers/Dockerfile_Tips.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Dockerfile_Tips.md)]
---

## Multi-dimensional versioning systems

Images can have a tag, indicating the version of the image.

But sometimes, there are multiple important components, and we need to indicate the versions
for all of them.

This can be done with environment variables:

```dockerfile
ENV PIP=9.0.3 \
    ZC_BUILDOUT=2.11.2 \
    SETUPTOOLS=38.7.0 \
    PLONE_MAJOR=5.1 \
    PLONE_VERSION=5.1.0 \
    PLONE_MD5=76dc6cfc1c749d763c32fff3a9870d8d
```

(Source: [Plone official image](https://github.com/plone/plone.docker/blob/master/5.1/5.1.0/alpine/Dockerfile))

.debug[[containers/Dockerfile_Tips.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Dockerfile_Tips.md)]
---

## Entrypoints and wrappers

It is very common to define a custom entrypoint.

That entrypoint will generally be a script, performing any combination of:

- pre-flights checks (if a required dependency is not available, display
  a nice error message early instead of an obscure one in a deep log file),

- generation or validation of configuration files,

- dropping privileges (with e.g. `su` or `gosu`, sometimes combined with `chown`),

- and more.

.debug[[containers/Dockerfile_Tips.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Dockerfile_Tips.md)]
---

## A typical entrypoint script

```dockerfile
 #!/bin/sh
 set -e
 
 # first arg is '-f' or '--some-option'
 # or first arg is 'something.conf'
 if [ "${1#-}" != "$1" ] || [ "${1%.conf}" != "$1" ]; then
 	set -- redis-server "$@"
 fi
 
 # allow the container to be started with '--user'
 if [ "$1" = 'redis-server' -a "$(id -u)" = '0' ]; then
 	chown -R redis .
 	exec su-exec redis "$0" "$@"
 fi
 
 exec "$@"
```

(Source: [Redis official image](https://github.com/docker-library/redis/blob/d24f2be82673ccef6957210cc985e392ebdc65e4/4.0/alpine/docker-entrypoint.sh))

.debug[[containers/Dockerfile_Tips.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Dockerfile_Tips.md)]
---

## Factoring information

To facilitate maintenance (and avoid human errors), avoid to repeat information like:

- version numbers,

- remote asset URLs (e.g. source tarballs) ...

Instead, use environment variables.

.small[
```dockerfile
ENV NODE_VERSION 10.2.1
...
RUN ...
    && curl -fsSLO --compressed "https://nodejs.org/dist/v$NODE_VERSION/node-v$NODE_VERSION.tar.xz" \
    && curl -fsSLO --compressed "https://nodejs.org/dist/v$NODE_VERSION/SHASUMS256.txt.asc" \
    && gpg --batch --decrypt --output SHASUMS256.txt SHASUMS256.txt.asc \
    && grep " node-v$NODE_VERSION.tar.xz\$" SHASUMS256.txt | sha256sum -c - \
    && tar -xf "node-v$NODE_VERSION.tar.xz" \
    && cd "node-v$NODE_VERSION" \
...
```
]

(Source: [Nodejs official image](https://github.com/nodejs/docker-node/blob/master/10/alpine/Dockerfile))

.debug[[containers/Dockerfile_Tips.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Dockerfile_Tips.md)]
---

## Overrides

In theory, development and production images should be the same.

In practice, we often need to enable specific behaviors in development (e.g. debug statements).

One way to reconcile both needs is to use Compose to enable these behaviors.

Let's look at the [trainingwheels](https://github.com/jpetazzo/trainingwheels) demo app for an example.

.debug[[containers/Dockerfile_Tips.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Dockerfile_Tips.md)]
---

## Production image

This Dockerfile builds an image leveraging gunicorn:

```dockerfile
FROM python
RUN pip install flask
RUN pip install gunicorn
RUN pip install redis
COPY . /src
WORKDIR /src
CMD gunicorn --bind 0.0.0.0:5000 --workers 10 counter:app
EXPOSE 5000
```

(Source: [trainingwheels Dockerfile](https://github.com/jpetazzo/trainingwheels/blob/master/www/Dockerfile))

.debug[[containers/Dockerfile_Tips.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Dockerfile_Tips.md)]
---

## Development Compose file

This Compose file uses the same image, but with a few overrides for development:

- the Flask development server is used (overriding `CMD`),

- the `DEBUG` environment variable is set,

- a volume is used to provide a faster local development workflow.

.small[
```yaml
services:
  www:
    build: www
    ports:
      - 8000:5000
    user: nobody
    environment:
      DEBUG: 1
    command: python counter.py
    volumes:
      - ./www:/src
```
]

(Source: [trainingwheels Compose file](https://github.com/jpetazzo/trainingwheels/blob/master/docker-compose.yml))

.debug[[containers/Dockerfile_Tips.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Dockerfile_Tips.md)]
---

## How to know which best practices are better?

- The main goal of containers is to make our lives easier.

- In this chapter, we showed many ways to write Dockerfiles.

- These Dockerfiles use sometimes diametrically opposed techniques.

- Yet, they were the "right" ones *for a specific situation.*

- It's OK (and even encouraged) to start simple and evolve as needed.

- Feel free to review this chapter later (after writing a few Dockerfiles) for inspiration!

???

:EN:Optimizing images
:EN:- Dockerfile tips, tricks, and best practices
:EN:- Reducing build time
:EN:- Reducing image size

:FR:Optimiser ses images
:FR:- Bonnes pratiques, trucs et astuces
:FR:- Réduire le temps de build
:FR:- Réduire la taille des images

.debug[[containers/Dockerfile_Tips.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Dockerfile_Tips.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/container-housing.jpg)]

---

Advanced Dockerfile Syntax

.nav[
[Previous part](#toc-dockerfile-examples)
|
[Back to table of contents](#toc-part-3)
|
[Next part](#toc-reducing-image-size)
]

---

# Advanced Dockerfile Syntax

![construction](images/title-advanced-dockerfiles.jpg)

.debug[[containers/Advanced_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Advanced_Dockerfiles.md)]
---

## Objectives

We have seen simple Dockerfiles to illustrate how Docker build
container images.

In this section, we will give a recap of the Dockerfile syntax,
and introduce advanced Dockerfile commands that we might
come across sometimes; or that we might want to use in some
specific scenarios.

.debug[[containers/Advanced_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Advanced_Dockerfiles.md)]
---

## `Dockerfile` usage summary

* `Dockerfile` instructions are executed in order.

* Each instruction creates a new layer in the image.

* Docker maintains a cache with the layers of previous builds.

* When there are no changes in the instructions and files making a layer,
  the builder re-uses the cached layer, without executing the instruction for that layer.

* The `FROM` instruction MUST be the first non-comment instruction.

* Lines starting with `#` are treated as comments.

* Some instructions (like `CMD` or `ENTRYPOINT`) update a piece of metadata.

(As a result, each call to these instructions makes the previous one useless.)

.debug[[containers/Advanced_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Advanced_Dockerfiles.md)]
---

## The `RUN` instruction

The `RUN` instruction can be specified in two ways.

With shell wrapping, which runs the specified command inside a shell,
with `/bin/sh -c`:

```dockerfile
RUN apt-get update
```

Or using the `exec` method, which avoids shell string expansion, and
allows execution in images that don't have `/bin/sh`:

```dockerfile
RUN [ "apt-get", "update" ]
```

.debug[[containers/Advanced_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Advanced_Dockerfiles.md)]
---

## More about the `RUN` instruction

`RUN` will do the following:

* Execute a command.
* Record changes made to the filesystem.
* Work great to install libraries, packages, and various files.

`RUN` will NOT do the following:

* Record state of *processes*.
* Automatically start daemons.

If you want to start something automatically when the container runs,
you should use `CMD` and/or `ENTRYPOINT`.

.debug[[containers/Advanced_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Advanced_Dockerfiles.md)]
---

## Collapsing layers

It is possible to execute multiple commands in a single step:

```dockerfile
RUN apt-get update && apt-get install -y wget && apt-get clean
```

It is also possible to break a command onto multiple lines:

```dockerfile
RUN apt-get update \
 && apt-get install -y wget \
 && apt-get clean
```

.debug[[containers/Advanced_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Advanced_Dockerfiles.md)]
---

## The `EXPOSE` instruction

The `EXPOSE` instruction tells Docker what ports are to be published
in this image.

```dockerfile
EXPOSE 8080
EXPOSE 80 443
EXPOSE 53/tcp 53/udp
```

* All ports are private by default.

* Declaring a port with `EXPOSE` is not enough to make it public.

* The `Dockerfile` doesn't control on which port a service gets exposed.

.debug[[containers/Advanced_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Advanced_Dockerfiles.md)]
---

## Exposing ports

* When you `docker run -p <port> ...`, that port becomes public.

(Even if it was not declared with `EXPOSE`.)

* When you `docker run -P ...` (without port number), all ports
  declared with `EXPOSE` become public.

A *public port* is reachable from other containers and from outside the host.

A *private port* is not reachable from outside.

.debug[[containers/Advanced_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Advanced_Dockerfiles.md)]
---

## The `COPY` instruction

The `COPY` instruction adds files and content from your host into the
image.

```dockerfile
COPY . /src
```

This will add the contents of the *build context* (the directory
passed as an argument to `docker build`) to the directory `/src`
in the container.

.debug[[containers/Advanced_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Advanced_Dockerfiles.md)]
---

## Build context isolation

Note: you can only reference files and directories *inside* the
build context. Absolute paths are taken as being anchored to
the build context, so the two following lines are equivalent:

```dockerfile
COPY . /src
COPY / /src
```

Attempts to use `..` to get out of the build context will be
detected and blocked with Docker, and the build will fail.

Otherwise, a `Dockerfile` could succeed on host A, but fail on host B.

.debug[[containers/Advanced_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Advanced_Dockerfiles.md)]
---

## `ADD`

`ADD` works almost like `COPY`, but has a few extra features.

`ADD` can get remote files:

```dockerfile
ADD http://www.example.com/webapp.jar /opt/
```

This would download the `webapp.jar` file and place it in the `/opt`
directory.

`ADD` will automatically unpack zip files and tar archives:

```dockerfile
ADD ./assets.zip /var/www/htdocs/assets/
```

This would unpack `assets.zip` into `/var/www/htdocs/assets`.

*However,* `ADD` will not automatically unpack remote archives.

.debug[[containers/Advanced_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Advanced_Dockerfiles.md)]
---

## `ADD`, `COPY`, and the build cache

* Before creating a new layer, Docker checks its build cache.

* For most Dockerfile instructions, Docker only looks at the
  `Dockerfile` content to do the cache lookup.

* For `ADD` and `COPY` instructions, Docker also checks if the files
  to be added to the container have been changed.

* `ADD` always needs to download the remote file before
  it can check if it has been changed.

(It cannot use,
  e.g., ETags or If-Modified-Since headers.)

.debug[[containers/Advanced_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Advanced_Dockerfiles.md)]
---

## `VOLUME`

The `VOLUME` instruction tells Docker that a specific directory
should be a *volume*.

```dockerfile
VOLUME /var/lib/mysql
```

Filesystem access in volumes bypasses the copy-on-write layer,
offering native performance to I/O done in those directories.

Volumes can be attached to multiple containers, allowing to
"port" data over from a container to another, e.g. to
upgrade a database to a newer version.

It is possible to start a container in "read-only" mode.
The container filesystem will be made read-only, but volumes
can still have read/write access if necessary.

.debug[[containers/Advanced_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Advanced_Dockerfiles.md)]
---

## The `WORKDIR` instruction

The `WORKDIR` instruction sets the working directory for subsequent
instructions.

It also affects `CMD` and `ENTRYPOINT`, since it sets the working
directory used when starting the container.
   
```dockerfile
WORKDIR /src
```

You can specify `WORKDIR` again to change the working directory for
further operations.

.debug[[containers/Advanced_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Advanced_Dockerfiles.md)]
---

## The `ENV` instruction

The `ENV` instruction specifies environment variables that should be
set in any container launched from the image.

```dockerfile
ENV WEBAPP_PORT 8080
```

This will result in an environment variable being created in any
containers created from this image of

```bash
WEBAPP_PORT=8080
```

You can also specify environment variables when you use `docker run`.

```bash
$ docker run -e WEBAPP_PORT=8000 -e WEBAPP_HOST=www.example.com ...
```

.debug[[containers/Advanced_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Advanced_Dockerfiles.md)]
---

## The `USER` instruction

The `USER` instruction sets the user name or UID to use when running
the image.

It can be used multiple times to change back to root or to another user.

.debug[[containers/Advanced_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Advanced_Dockerfiles.md)]
---

## The `CMD` instruction

The `CMD` instruction is a default command run when a container is
launched from the image.

```dockerfile
CMD [ "nginx", "-g", "daemon off;" ]
```

Means we don't need to specify `nginx -g "daemon off;"` when running the
container.

Instead of:

```bash
$ docker run <dockerhubUsername>/web_image nginx -g "daemon off;"
```

We can just do:

```bash
$ docker run <dockerhubUsername>/web_image
```

.debug[[containers/Advanced_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Advanced_Dockerfiles.md)]
---

## More about the `CMD` instruction

Just like `RUN`, the `CMD` instruction comes in two forms.
The first executes in a shell:

```dockerfile
CMD nginx -g "daemon off;"
```

The second executes directly, without shell processing:

```dockerfile
CMD [ "nginx", "-g", "daemon off;" ]
```

.debug[[containers/Advanced_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Advanced_Dockerfiles.md)]
---

## Overriding the `CMD` instruction

The `CMD` can be overridden when you run a container.

```bash
$ docker run -it <dockerhubUsername>/web_image bash
```

Will run `bash` instead of `nginx -g "daemon off;"`.

.debug[[containers/Advanced_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Advanced_Dockerfiles.md)]
---

## The `ENTRYPOINT` instruction

The `ENTRYPOINT` instruction is like the `CMD` instruction,
but arguments given on the command line are *appended* to the
entry point.

Note: you have to use the "exec" syntax (`[ "..." ]`).

```dockerfile
ENTRYPOINT [ "/bin/ls" ]
```

If we were to run:

```bash
$ docker run training/ls -l
```

Instead of trying to run `-l`, the container will run `/bin/ls -l`.

.debug[[containers/Advanced_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Advanced_Dockerfiles.md)]
---

## Overriding the `ENTRYPOINT` instruction

The entry point can be overridden as well.

```bash
$ docker run -it training/ls
bin   dev  home  lib64  mnt  proc  run   srv  tmp  var
boot  etc  lib   media  opt  root  sbin  sys  usr
$ docker run -it --entrypoint bash training/ls
root@d902fb7b1fc7:/#
```

.debug[[containers/Advanced_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Advanced_Dockerfiles.md)]
---

## How `CMD` and `ENTRYPOINT` interact

The `CMD` and `ENTRYPOINT` instructions work best when used
together.

```dockerfile
ENTRYPOINT [ "nginx" ]
CMD [ "-g", "daemon off;" ]
```

The `ENTRYPOINT` specifies the command to be run and the `CMD`
specifies its options. On the command line we can then potentially
override the options when needed.

```bash
$ docker run -d <dockerhubUsername>/web_image -t
```

This will override the options `CMD` provided with new flags.

.debug[[containers/Advanced_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Advanced_Dockerfiles.md)]
---

## Advanced Dockerfile instructions

* `ONBUILD` lets you stash instructions that will be executed
  when this image is used as a base for another one.
* `LABEL` adds arbitrary metadata to the image.
* `ARG` defines build-time variables (optional or mandatory).
* `STOPSIGNAL` sets the signal for `docker stop` (`TERM` by default).
* `HEALTHCHECK` defines a command assessing the status of the container.
* `SHELL` sets the default program to use for string-syntax RUN, CMD, etc.

.debug[[containers/Advanced_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Advanced_Dockerfiles.md)]
---

## The `ONBUILD` instruction

The `ONBUILD` instruction is a trigger. It sets instructions that will
be executed when another image is built from the image being build.

This is useful for building images which will be used as a base
to build other images.

```dockerfile
ONBUILD COPY . /src
```

* You can't chain `ONBUILD` instructions with `ONBUILD`.
* `ONBUILD` can't be used to trigger `FROM` instructions.

???

:EN:- Advanced Dockerfile syntax
:FR:- Dockerfile niveau expert

.debug[[containers/Advanced_Dockerfiles.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Advanced_Dockerfiles.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/containers-by-the-water.jpg)]

---

Reducing image size

.nav[
[Previous part](#toc-advanced-dockerfile-syntax)
|
[Back to table of contents](#toc-part-3)
|
[Next part](#toc-multi-stage-builds)
]

---
# Reducing image size

* In the previous example, our final image contained:

* our `hello` program

* its source code

* the compiler

* Only the first one is strictly necessary.

* We are going to see how to obtain an image without the superfluous components.

.debug[[containers/Multi_Stage_Builds.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Multi_Stage_Builds.md)]
---

## Can't we remove superfluous files with `RUN`?

What happens if we do one of the following commands?

- `RUN rm -rf ...`

- `RUN apt-get remove ...`

- `RUN make clean ...`

This adds a layer which removes a bunch of files.

But the previous layers (which added the files) still exist.

.debug[[containers/Multi_Stage_Builds.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Multi_Stage_Builds.md)]
---

## Removing files with an extra layer

When downloading an image, all the layers must be downloaded.

| Dockerfile instruction | Layer size | Image size |
| ---------------------- | ---------- | ---------- |
| `FROM ubuntu` | Size of base image | Size of base image |
| `...` | ... | Sum of this layer + all previous ones |
| `RUN apt-get install somepackage` | Size of files added (e.g. a few MB) | Sum of this layer + all previous ones |
| `...` | ... | Sum of this layer + all previous ones |
| `RUN apt-get remove somepackage` | Almost zero (just metadata) | Same as previous one |

Therefore, `RUN rm` does not reduce the size of the image or free up disk space.

.debug[[containers/Multi_Stage_Builds.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Multi_Stage_Builds.md)]
---

## Removing unnecessary files

Various techniques are available to obtain smaller images:

- collapsing layers,

- adding binaries that are built outside of the Dockerfile,

- squashing the final image,

- multi-stage builds.

Let's review them quickly.

.debug[[containers/Multi_Stage_Builds.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Multi_Stage_Builds.md)]
---

## Collapsing layers

You will frequently see Dockerfiles like this:

```dockerfile
FROM ubuntu
RUN apt-get update && apt-get install xxx && ... && apt-get remove xxx && ...
```

Or the (more readable) variant:

```dockerfile
FROM ubuntu
RUN apt-get update \
 && apt-get install xxx \
 && ... \
 && apt-get remove xxx \
 && ...
```

This `RUN` command gives us a single layer.

The files that are added, then removed in the same layer, do not grow the layer size.

.debug[[containers/Multi_Stage_Builds.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Multi_Stage_Builds.md)]
---

## Collapsing layers: pros and cons

Pros:

- works on all versions of Docker

- doesn't require extra tools

Cons:

- not very readable

- some unnecessary files might still remain if the cleanup is not thorough

- that layer is expensive (slow to build)

.debug[[containers/Multi_Stage_Builds.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Multi_Stage_Builds.md)]
---

## Building binaries outside of the Dockerfile

This results in a Dockerfile looking like this:

```dockerfile
FROM ubuntu
COPY xxx /usr/local/bin
```

Of course, this implies that the file `xxx` exists in the build context.

That file has to exist before you can run `docker build`.

For instance, it can:

- exist in the code repository,
- be created by another tool (script, Makefile...),
- be created by another container image and extracted from the image.

See for instance the [busybox official image](https://github.com/docker-library/busybox/blob/fe634680e32659aaf0ee0594805f74f332619a90/musl/Dockerfile) or this [older busybox image](https://github.com/jpetazzo/docker-busybox).

.debug[[containers/Multi_Stage_Builds.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Multi_Stage_Builds.md)]
---

## Building binaries outside: pros and cons

Pros:

- final image can be very small

Cons:

- requires an extra build tool

- we're back in dependency hell and "works on my machine"

Cons, if binary is added to code repository:

- breaks portability across different platforms

- grows repository size a lot if the binary is updated frequently

.debug[[containers/Multi_Stage_Builds.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Multi_Stage_Builds.md)]
---

## Squashing the final image

The idea is to transform the final image into a single-layer image.

This can be done in (at least) two ways.

- Activate experimental features and squash the final image:
  ```bash
  docker image build --squash ...
  ```

- Export/import the final image.
  ```bash
  docker build -t temp-image .
  docker run --entrypoint true --name temp-container temp-image
  docker export temp-container | docker import - final-image
  docker rm temp-container
  docker rmi temp-image
  ```

.debug[[containers/Multi_Stage_Builds.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Multi_Stage_Builds.md)]
---

## Squashing the image: pros and cons

Pros:

- single-layer images are smaller and faster to download

- removed files no longer take up storage and network resources

Cons:

- we still need to actively remove unnecessary files

- squash operation can take a lot of time (on big images)

- squash operation does not benefit from cache
 
 (even if we change just a tiny file, the whole image needs to be re-squashed)

.debug[[containers/Multi_Stage_Builds.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Multi_Stage_Builds.md)]
---

## Multi-stage builds

Multi-stage builds allow us to have multiple *stages*.

Each stage is a separate image, and can copy files from previous stages.

We're going to see how they work in more detail.

.debug[[containers/Multi_Stage_Builds.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Multi_Stage_Builds.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/distillery-containers.jpg)]

---

Multi-stage builds

.nav[
[Previous part](#toc-reducing-image-size)
|
[Back to table of contents](#toc-part-3)
|
[Next part](#toc-publishing-images-to-the-docker-hub)
]

---

# Multi-stage builds

* At any point in our `Dockerfile`, we can add a new `FROM` line.

* This line starts a new stage of our build.

* Each stage can access the files of the previous stages with `COPY --from=...`.

* When a build is tagged (with `docker build -t ...`), the last stage is tagged.

* Previous stages are not discarded: they will be used for caching, and can be referenced.

.debug[[containers/Multi_Stage_Builds.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Multi_Stage_Builds.md)]
---

## Multi-stage builds in practice

* Each stage is numbered, starting at `0`

* We can copy a file from a previous stage by indicating its number, e.g.:

```dockerfile
  COPY --from=0 /file/from/first/stage /location/in/current/stage
  ```

* We can also name stages, and reference these names:

```dockerfile
  FROM golang AS builder
  RUN ...
  FROM alpine
  COPY --from=builder /go/bin/mylittlebinary /usr/local/bin/
  ```

.debug[[containers/Multi_Stage_Builds.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Multi_Stage_Builds.md)]
---

## Multi-stage builds for our C program

We will change our Dockerfile to:

* give a nickname to the first stage: `compiler`

* add a second stage using the same `ubuntu` base image

* add the `hello` binary to the second stage

* make sure that `CMD` is in the second stage

The resulting Dockerfile is on the next slide.

.debug[[containers/Multi_Stage_Builds.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Multi_Stage_Builds.md)]
---

## Multi-stage build `Dockerfile`

Here is the final Dockerfile:

```dockerfile
FROM ubuntu AS compiler
RUN apt-get update
RUN apt-get install -y build-essential
COPY hello.c /
RUN make hello
FROM ubuntu
COPY --from=compiler /hello /hello
CMD /hello
```

Let's build it, and check that it works correctly:

```bash
docker build -t hellomultistage .
docker run hellomultistage
```

.debug[[containers/Multi_Stage_Builds.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Multi_Stage_Builds.md)]
---

## Comparing single/multi-stage build image sizes

List our images with `docker images`, and check the size of:

- the `ubuntu` base image,

- the single-stage `hello` image,

- the multi-stage `hellomultistage` image.

We can achieve even smaller images if we use smaller base images.

However, if we use common base images (e.g. if we standardize on `ubuntu`),
these common images will be pulled only once per node, so they are
virtually "free."

.debug[[containers/Multi_Stage_Builds.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Multi_Stage_Builds.md)]
---

## Build targets

* We can also tag an intermediary stage with the following command:
  ```bash
  docker build --target STAGE --tag NAME
  ```

* This will create an image (named `NAME`) corresponding to stage `STAGE`

* This can be used to easily access an intermediary stage for inspection

(instead of parsing the output of `docker build` to find out the image ID)

* This can also be used to describe multiple images from a single Dockerfile

(instead of using multiple Dockerfiles, which could go out of sync)

???

:EN:Optimizing our images and their build process
:EN:- Leveraging multi-stage builds

:FR:Optimiser les images et leur construction
:FR:- Utilisation d'un *multi-stage build*

.debug[[containers/Multi_Stage_Builds.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Multi_Stage_Builds.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/lots-of-containers.jpg)]

---

Publishing images to the Docker Hub

.nav[
[Previous part](#toc-multi-stage-builds)
|
[Back to table of contents](#toc-part-3)
|
[Next part](#toc-exercise--writing-better-dockerfiles)
]

---
# Publishing images to the Docker Hub

We have built our first images.

We can now publish it to the Docker Hub!

*You don't have to do the exercises in this section,
because they require an account on the Docker Hub, and we
don't want to force anyone to create one.*

*Note, however, that creating an account on the Docker Hub
is free (and doesn't require a credit card), and hosting
public images is free as well.*

.debug[[containers/Publishing_To_Docker_Hub.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Publishing_To_Docker_Hub.md)]
---

## Logging into our Docker Hub account

* This can be done from the Docker CLI:
  ```bash
  docker login
  ```

.warning[When running Docker for Mac/Windows, or
Docker on a Linux workstation, it can (and will when
possible) integrate with your system's keyring to
store your credentials securely. However, on most Linux
servers, it will store your credentials in `~/.docker/config`.]

.debug[[containers/Publishing_To_Docker_Hub.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Publishing_To_Docker_Hub.md)]
---

## Image tags and registry addresses

* Docker images tags are like Git tags and branches.

* They are like *bookmarks* pointing at a specific image ID.

* Tagging an image doesn't *rename* an image: it adds another tag.

* When pushing an image to a registry, the registry address is in the tag.

Example: `registry.example.net:5000/image`

* What about Docker Hub images?

* `jpetazzo/clock` is, in fact, `index.docker.io/jpetazzo/clock`

* `ubuntu` is, in fact, `library/ubuntu`, i.e. `index.docker.io/library/ubuntu`

.debug[[containers/Publishing_To_Docker_Hub.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Publishing_To_Docker_Hub.md)]
---

## Tagging an image to push it on the Hub

* Let's tag our `figlet` image (or any other to our liking):
  ```bash
  docker tag figlet jpetazzo/figlet
  ```

* And push it to the Hub:
  ```bash
  docker push jpetazzo/figlet
  ```

* That's it!

* Anybody can now `docker run jpetazzo/figlet` anywhere.

.debug[[containers/Publishing_To_Docker_Hub.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Publishing_To_Docker_Hub.md)]
---

## The goodness of automated builds

* You can link a Docker Hub repository with a GitHub or BitBucket repository

* Each push to GitHub or BitBucket will trigger a build on Docker Hub

* If the build succeeds, the new image is available on Docker Hub

* You can map tags and branches between source and container images

* If you work with public repositories, this is free

.debug[[containers/Publishing_To_Docker_Hub.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Publishing_To_Docker_Hub.md)]
---

## Setting up an automated build

* We need a Dockerized repository!
* Let's go to https://github.com/jpetazzo/trainingwheels and fork it.
* Go to the Docker Hub (https://hub.docker.com/) and sign-in. Select "Repositories" in the blue navigation menu.
* Select "Create" in the top-right bar, and select "Create Repository+".
* Connect your Docker Hub account to your GitHub account.
* Click "Create" button.
* Then go to "Builds" folder.
* Click on Github icon and select your user and the repository that we just forked.
* In "Build rules" block near page bottom, put `/www` in "Build Context" column (or whichever directory the Dockerfile is in).
* Click "Save and Build" to build the repository immediately (without waiting for a git push).
* Subsequent builds will happen automatically, thanks to GitHub hooks.

.debug[[containers/Publishing_To_Docker_Hub.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Publishing_To_Docker_Hub.md)]
---

## Building on the fly

- Some services can build images on the fly from a repository

- Example: [ctr.run](https://ctr.run/)

- Use ctr.run to automatically build a container image and run it:
  ```bash
  docker run ctr.run/github.com/undefinedlabs/hello-world
  ```

]

There might be a long pause before the first layer is pulled,
because the API behind `docker pull` doesn't allow to stream build logs, and there is no feedback during the build.

It is possible to view the build logs by setting up an account on [ctr.run](https://ctr.run/).

???

:EN:- Publishing images to the Docker Hub
:FR:- Publier des images sur le Docker Hub

.debug[[containers/Publishing_To_Docker_Hub.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Publishing_To_Docker_Hub.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/plastic-containers.JPG)]

---

Exercise — writing better Dockerfiles

.nav[
[Previous part](#toc-publishing-images-to-the-docker-hub)
|
[Back to table of contents](#toc-part-3)
|
[Next part](#toc-buildkit)
]

---
# Exercise — writing better Dockerfiles

Let's update our Dockerfiles to leverage multi-stage builds!

The code is at: https://github.com/jpetazzo/wordsmith

Use a different tag for these images, so that we can compare their sizes.

What's the size difference between single-stage and multi-stage builds?

.debug[[containers/Exercise_Dockerfile_Advanced.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Exercise_Dockerfile_Advanced.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/train-of-containers-1.jpg)]

---

Buildkit

.nav[
[Previous part](#toc-exercise--writing-better-dockerfiles)
|
[Back to table of contents](#toc-part-4)
|
[Next part](#toc-container-network-drivers)
]

---
# Buildkit

- "New" backend for Docker builds

- announced in 2017

- ships with Docker Engine 18.09

- enabled by default on Docker Desktop in 2021

- Huge improvements in build efficiency

- 100% compatible with existing Dockerfiles

- New features for multi-arch

- Not just for building container images

.debug[[containers/Buildkit.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Buildkit.md)]
---

## Old vs New

- Classic `docker build`:

- copy whole build context
  - linear execution
  - `docker run` + `docker commit` + `docker run` + `docker commit`...

- Buildkit:

- copy files only when they are needed; cache them
  - compute dependency graph (dependencies are expressed by `COPY`)
  - parallel execution
  - doesn't rely on Docker, but on internal runner/snapshotter
  - can run in "normal" containers (including in Kubernetes pods)

.debug[[containers/Buildkit.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Buildkit.md)]
---

## Parallel execution

- In multi-stage builds, all stages can be built in parallel

(example: https://github.com/jpetazzo/shpod; [before] and [after])

- Stages are built only when they are necessary

(i.e. if their output is tagged or used in another necessary stage)

- Files are copied from context only when needed

- Files are cached in the builder

[before]: https://github.com/jpetazzo/shpod/blob/c6efedad6d6c3dc3120dbc0ae0a6915f85862474/Dockerfile
[after]: https://github.com/jpetazzo/shpod/blob/d20887bbd56b5fcae2d5d9b0ce06cae8887caabf/Dockerfile

.debug[[containers/Buildkit.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Buildkit.md)]
---

## Turning it on and off

- On recent version of Docker Desktop (since 2021):

*enabled by default*

- On older versions, or on Docker CE (Linux):

`export DOCKER_BUILDKIT=1`

- Turning it off:

`export DOCKER_BUILDKIT=0`

.debug[[containers/Buildkit.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Buildkit.md)]
---

## Multi-arch support

- Historically, Docker only ran on x86_64 / amd64

(Intel/AMD 64 bits architecture)

- Folks have been running it on 32-bit ARM for ages

(e.g. Raspberry Pi)

- This required a Go compiler and appropriate base images

(which means changing/adapting Dockerfiles to use these base images)

- Docker [image manifest v2 schema 2][manifest] introduces multi-arch images

(`FROM alpine` automatically gets the right image for your architecture)

[manifest]: https://docs.docker.com/registry/spec/manifest-v2-2/

.debug[[containers/Buildkit.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Buildkit.md)]
---

## Why?

- Raspberry Pi (32-bit and 64-bit ARM)

- Other ARM-based embedded systems (ODROID, NVIDIA Jetson...)

- Apple M1

- AWS Graviton

- Ampere Altra (e.g. on Oracle Cloud)

- ...

.debug[[containers/Buildkit.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Buildkit.md)]
---

## Multi-arch builds in a nutshell

Use the `docker buildx build` command:

```bash
docker buildx build … \
       --platform linux/amd64,linux/arm64,linux/arm/v7,linux/386 \
       [--tag jpetazzo/hello --push]
```

- Requires all base images to be available for these platforms

- Must not use binary downloads with hard-coded architectures!

(streamlining a Dockerfile for multi-arch: [before], [after])

[before]: https://github.com/jpetazzo/shpod/blob/d20887bbd56b5fcae2d5d9b0ce06cae8887caabf/Dockerfile
[after]: https://github.com/jpetazzo/shpod/blob/c50789e662417b34fea6f5e1d893721d66d265b7/Dockerfile

.debug[[containers/Buildkit.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Buildkit.md)]
---

## Native vs emulated vs cross

- Native builds:

*aarch64 machine running aarch64 programs building aarch64 images/binaries*

- Emulated builds:

*x86_64 machine running aarch64 programs building aarch64 images/binaries*

- Cross builds:

*x86_64 machine running x86_64 programs building aarch64 images/binaries*

.debug[[containers/Buildkit.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Buildkit.md)]
---

## Native

- Dockerfiles are (relatively) simple to write

(nothing special to do to handle multi-arch; just avoid hard-coded archs)

- Best performance

- Requires "exotic" machines

- Requires setting up a build farm

.debug[[containers/Buildkit.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Buildkit.md)]
---

## Emulated

- Dockerfiles are (relatively) simple to write

- Emulation performance can vary

(from "OK" to "ouch this is slow")

- Emulation isn't always perfect

(weird bugs/crashes are rare but can happen)

- Doesn't require special machines

- Supports arbitrary architectures thanks to QEMU

.debug[[containers/Buildkit.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Buildkit.md)]
---

## Cross

- Dockerfiles are more complicated to write

- Requires cross-compilation toolchains

- Performance is good

- Doesn't require special machines

.debug[[containers/Buildkit.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Buildkit.md)]
---

## Native builds

- Requires base images to be available

- To view available architectures for an image:
 ```bash
 regctl manifest get --list <imagename>
 docker manifest inspect <imagename>
 ```

- Nothing special to do, *except* when downloading binaries!

```
  https://releases.hashicorp.com/terraform/1.1.5/terraform_1.1.5_linux_`amd64`.zip
  ```

.debug[[containers/Buildkit.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Buildkit.md)]
---

## Finding the right architecture

`uname -m` → armv7l, aarch64, i686, x86_64

`GOARCH` (from `go env`) → arm, arm64, 386, amd64

In Dockerfile, add `ARG TARGETARCH` (or `ARG TARGETPLATFORM`)

- `TARGETARCH` matches `GOARCH`

- `TARGETPLAFORM` → linux/arm/v7, linux/arm64, linux/386, linux/amd64

.debug[[containers/Buildkit.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Buildkit.md)]
---

## Welp

Sometimes, binary releases be like:

```
Linux_arm64.tar.gz
Linux_ppc64le.tar.gz
Linux_s390x.tar.gz
Linux_x86_64.tar.gz 
```

This needs a bit of custom mapping.

.debug[[containers/Buildkit.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Buildkit.md)]
---

## Emulation

- Leverages `binfmt_misc` and QEMU on Linux

- Enabling:
  ```bash
  docker run --rm --privileged aptman/qus -s -- -p
  ```

- Disabling:
  ```bash
  docker run --rm --privileged aptman/qus -- -r
  ```

- Checking status:
  ```bash
  ls -l /proc/sys/fs/binfmt_misc
  ```

.debug[[containers/Buildkit.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Buildkit.md)]
---

## How it works

- `binfmt_misc` lets us register _interpreters_ for binaries, e.g.:

- [DOSBox][dosbox] for DOS programs

- [Wine][wine] for Windows programs

- [QEMU][qemu] for Linux programs for other architectures

- When we try to execute e.g. a SPARC binary on our x86_64 machine:

- `binfmt_misc` detects the binary format and invokes `qemu-<arch> the-binary ...`

- QEMU translates SPARC instructions to x86_64 instructions

- system calls go straight to the kernel

[dosbox]: https://www.dosbox.com/
[QEMU]: https://www.qemu.org/
[wine]: https://www.winehq.org/

.debug[[containers/Buildkit.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Buildkit.md)]
---

## QEMU registration

- The `aptman/qus` image mentioned earlier contains static QEMU builds

- It registers all these interpreters with the kernel

- For more details, check:

- https://github.com/dbhi/qus

- https://dbhi.github.io/qus/

.debug[[containers/Buildkit.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Buildkit.md)]
---

## Cross-compilation

- Cross-compilation is about 10x faster than emulation

(non-scientific benchmarks!)

- In Dockerfile, add:

`ARG BUILDARCH BUILDPLATFORM TARGETARCH TARGETPLATFORM`

- Can use `FROM --platform=$BUILDPLATFORM <image>`

- Then use `$TARGETARCH` or `$TARGETPLATFORM`

(e.g. for Go, `export GOARCH=$TARGETARCH`)

- Check [tonistiigi/xx][xx] and [Toni's blog][toni] for some amazing cross tools!

[xx]: https://github.com/tonistiigi/xx
[toni]: https://medium.com/@tonistiigi/faster-multi-platform-builds-dockerfile-cross-compilation-guide-part-1-ec087c719eaf

.debug[[containers/Buildkit.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Buildkit.md)]
---

## Checking runtime capabilities

Build and run the following Dockerfile:

```dockerfile
FROM --platform=linux/amd64 busybox AS amd64
FROM --platform=linux/arm64 busybox AS arm64
FROM --platform=linux/arm/v7 busybox AS arm32
FROM --platform=linux/386 busybox AS ia32
FROM alpine
RUN apk add file
WORKDIR /root
COPY --from=amd64 /bin/busybox /root/amd64/busybox
COPY --from=arm64 /bin/busybox /root/arm64/busybox
COPY --from=arm32 /bin/busybox /root/arm32/busybox
COPY --from=ia32 /bin/busybox /root/ia32/busybox
CMD for A in *; do echo "$A => $($A/busybox uname -a)"; done
```

It will indicate which executables can be run on your engine.

.debug[[containers/Buildkit.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Buildkit.md)]
---

## More than builds

- Buildkit is also used in other systems:

- [Earthly] - generic repeatable build pipelines

- [Dagger] - CICD pipelines that run anywhere

- and more!

[Earthly]: https://earthly.dev/
[Dagger]: https://dagger.io/

.debug[[containers/Buildkit.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Buildkit.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/train-of-containers-2.jpg)]

---

Container network drivers

.nav[
[Previous part](#toc-buildkit)
|
[Back to table of contents](#toc-part-4)
|
[Next part](#toc-deep-dive-into-container-internals)
]

---
# Container network drivers

The Docker Engine supports different network drivers.

The built-in drivers include:

* `bridge` (default)

* `null` (for the special network called `none`)

* `host` (for the special network called `host`)

* `container` (that one is a bit magic!)

The network is selected with `docker run --net ...`.

Each network is managed by a driver.

The different drivers are explained with more details on the following slides.

.debug[[containers/Network_Drivers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Network_Drivers.md)]
---

## The default bridge

* By default, the container gets a virtual `eth0` interface.
 (In addition to its own private `lo` loopback interface.)

* That interface is provided by a `veth` pair.

* It is connected to the Docker bridge.
 (Named `docker0` by default; configurable with `--bridge`.)

* Addresses are allocated on a private, internal subnet.
 (Docker uses 172.17.0.0/16 by default; configurable with `--bip`.)

* Outbound traffic goes through an iptables MASQUERADE rule.

* Inbound traffic goes through an iptables DNAT rule.

* The container can have its own routes, iptables rules, etc.

.debug[[containers/Network_Drivers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Network_Drivers.md)]
---

## The null driver

* Container is started with `docker run --net none ...`

* It only gets the `lo` loopback interface. No `eth0`.

* It can't send or receive network traffic.

* Useful for isolated/untrusted workloads.

.debug[[containers/Network_Drivers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Network_Drivers.md)]
---

## The host driver

* Container is started with `docker run --net host ...`

* It sees (and can access) the network interfaces of the host.

* It can bind any address, any port (for ill and for good).

* Network traffic doesn't have to go through NAT, bridge, or veth.

* Performance = native!

Use cases:

* Performance sensitive applications (VOIP, gaming, streaming...)

* Peer discovery (e.g. Erlang port mapper, Raft, Serf...)

.debug[[containers/Network_Drivers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Network_Drivers.md)]
---

## The container driver

* Container is started with `docker run --net container:id ...`

* It re-uses the network stack of another container.

* It shares with this other container the same interfaces, IP address(es), routes, iptables rules, etc.

* Those containers can communicate over their `lo` interface.
 (i.e. one can bind to 127.0.0.1 and the others can connect to it.)

???

:EN:Advanced container networking
:EN:- Transparent network access with the "host" driver
:EN:- Sharing is caring with the "container" driver

:FR:Paramétrage réseau avancé
:FR:- Accès transparent au réseau avec le mode "host"
:FR:- Partage de la pile réseau avece le mode "container"

.debug[[containers/Network_Drivers.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Network_Drivers.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/two-containers-on-a-truck.jpg)]

---

Deep dive into container internals

.nav[
[Previous part](#toc-container-network-drivers)
|
[Back to table of contents](#toc-part-4)
|
[Next part](#toc-control-groups)
]

---
# Deep dive into container internals

In this chapter, we will explain some of the fundamental building blocks of containers.

This will give you a solid foundation so you can:

- understand "what's going on" in complex situations,

- anticipate the behavior of containers (performance, security...) in new scenarios,

- implement your own container engine.

The last item should be done for educational purposes only!

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## There is no container code in the Linux kernel

- If we search "container" in the Linux kernel code, we find:

- generic code to manipulate data structures (like linked lists, etc.),

- unrelated concepts like "ACPI containers",

- *nothing* relevant to "our" containers!

- Containers are composed using multiple independent features.

- On Linux, containers rely on "namespaces, cgroups, and some filesystem magic."

- Security also requires features like capabilities, seccomp, LSMs...

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/wall-of-containers.jpeg)]

---

Control groups

.nav[
[Previous part](#toc-deep-dive-into-container-internals)
|
[Back to table of contents](#toc-part-4)
|
[Next part](#toc-namespaces)
]

---

# Control groups

- Control groups provide resource *metering* and *limiting*.

- This covers a number of "usual suspects" like:

- memory

- CPU

- block I/O

- network (with cooperation from iptables/tc)

- And a few exotic ones:

- huge pages (a special way to allocate memory)

- RDMA (resources specific to InfiniBand / remote memory transfer)

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Crowd control

- Control groups also allow to group processes for special operations:

- freezer (conceptually similar to a "mass-SIGSTOP/SIGCONT")

- perf_event (gather performance events on multiple processes)

- cpuset (limit or pin processes to specific CPUs)

- There is a "pids" cgroup to limit the number of processes in a given group.

- There is also a "devices" cgroup to control access to device nodes.

(i.e. everything in `/dev`.)

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Generalities

- Cgroups form a hierarchy (a tree).

- We can create nodes in that hierarchy.

- We can associate limits to a node.

- We can move a process (or multiple processes) to a node.

- The process (or processes) will then respect these limits.

- We can check the current usage of each node.

- In other words: limits are optional (if we only want accounting).

- When a process is created, it is placed in its parent's groups.

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Example

The numbers are PIDs.

The names are the names of our nodes (arbitrarily chosen).

.small[
```bash
cpu                      memory
├── batch                ├── stateless
│   ├── cryptoscam       │   ├── 25
│   │   └── 52           │   ├── 26
│   └── ffmpeg           │   ├── 27
│       ├── 109          │   ├── 52
│       └── 88           │   ├── 109
└── realtime             │   └── 88
    ├── nginx            └── databases
    │   ├── 25               ├── 1008
    │   ├── 26               └── 524
    │   └── 27
    ├── postgres
    │   └── 524
    └── redis
        └── 1008
```
]

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Cgroups v1 vs v2

- Cgroups v1 are available on all systems (and widely used).

- Cgroups v2 are a huge refactor.

(Development started in Linux 3.10, released in 4.5.)

- Cgroups v2 have a number of differences:

- single hierarchy (instead of one tree per controller),

- processes can only be on leaf nodes (not inner nodes),

- and of course many improvements / refactorings.

- Cgroups v2 enabled by default on Fedora 31 (2019), Ubuntu 21.10...

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Memory cgroup: accounting

- Keeps track of pages used by each group:

- file (read/write/mmap from block devices),
  - anonymous (stack, heap, anonymous mmap),
  - active (recently accessed),
  - inactive (candidate for eviction).

- Each page is "charged" to a group.

- Pages can be shared across multiple groups.

(Example: multiple processes reading from the same files.)

- To view all the counters kept by this cgroup:

```bash
  $ cat /sys/fs/cgroup/memory/memory.stat
  ```

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Memory cgroup v1: limits

- Each group can have (optional) hard and soft limits.

- Limits can be set for different kinds of memory:

- physical memory,

- kernel memory,

- total memory (including swap).

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Soft limits and hard limits

- Soft limits are not enforced.

(But they influence reclaim under memory pressure.)

- Hard limits *cannot* be exceeded:

- if a group of processes exceeds a hard limit,

- and if the kernel cannot reclaim any memory,

- then the OOM (out-of-memory) killer is triggered,

- and processes are killed until memory gets below the limit again.

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Avoiding the OOM killer

- For some workloads (databases and stateful systems), killing
  processes because we run out of memory is not acceptable.

- The "oom-notifier" mechanism helps with that.

- When "oom-notifier" is enabled and a hard limit is exceeded:

- all processes in the cgroup are frozen,

- a notification is sent to user space (instead of killing processes),

- user space can then raise limits, migrate containers, etc.,

- once the memory usage is below the hard limit, unfreeze the cgroup.

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Overhead of the memory cgroup

- Each time a process grabs or releases a page, the kernel update counters.

- This adds some overhead.

- Unfortunately, this cannot be enabled/disabled per process.

- It has to be done system-wide, at boot time.

- Also, when multiple groups use the same page:

- only the first group gets "charged",

- but if it stops using it, the "charge" is moved to another group.

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Setting up a limit with the memory cgroup

Create a new memory cgroup:

```bash
$ CG=/sys/fs/cgroup/memory/onehundredmegs
$ sudo mkdir $CG
```

Limit it to approximately 100MB of memory usage:

```bash
$ sudo tee $CG/memory.memsw.limit_in_bytes <<< 100000000
```

Move the current process to that cgroup:

```bash
$ sudo tee $CG/tasks <<< $$
```

The current process *and all its future children* are now limited.

(Confused about `<<<`? Look at the next slide!)

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## What's `<<<`?

- This is a "here string". (It is a non-POSIX shell extension.)

- The following commands are equivalent:

```bash
 foo <<< hello
 ```

```bash
  echo hello | foo
  ```

```bash
 foo <<EOF
 hello
 EOF
 ```

- Why did we use that?

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Writing to cgroups pseudo-files requires root

Instead of:

```bash
sudo tee $CG/tasks <<< $$
```

We could have done:

```bash
sudo sh -c "echo $$ > $CG/tasks"
```

The following commands, however, would be invalid:

```bash
sudo echo $$ > $CG/tasks
```

```bash
sudo -i # (or su)
echo $$ > $CG/tasks
```

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Testing the memory limit

Start the Python interpreter:

```bash
$ python
Python 3.6.4 (default, Jan  5 2018, 02:35:40)
[GCC 7.2.1 20171224] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>
```

Allocate 80 megabytes:

```python
>>> s = "!" * 1000000 * 80
```

Add 20 megabytes more:

```python
>>> t = "!" * 1000000 * 20
Killed
```

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Memory cgroup v2: limits

- `memory.min` = hard reservation (guaranteed memory for this cgroup)

- `memory.low` = soft reservation ("*try* not to reclaim memory if we're below this")

- `memory.high` = soft limit (aggressively reclaim memory; don't trigger OOMK)

- `memory.max` = hard limit (triggers OOMK)

- `memory.swap.high` = aggressively reclaim memory when using that much swap

- `memory.swap.max` = prevent using more swap than this

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## CPU cgroup

- Keeps track of CPU time used by a group of processes.

(This is easier and more accurate than `getrusage` and `/proc`.)

- Keeps track of usage per CPU as well.

(i.e., "this group of process used X seconds of CPU0 and Y seconds of CPU1".)

- Allows setting relative weights used by the scheduler.

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Cpuset cgroup

- Pin groups to specific CPU(s).

- Use-case: reserve CPUs for specific apps.

- Warning: make sure that "default" processes aren't using all CPUs!

- CPU pinning can also avoid performance loss due to cache flushes.

- This is also relevant for NUMA systems.

- Provides extra dials and knobs.

(Per zone memory pressure, process migration costs...)

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Blkio cgroup

- Keeps track of I/Os for each group:

- per block device
  - read vs write
  - sync vs async

- Set throttle (limits) for each group:

- per block device
  - read vs write
  - ops vs bytes

- Set relative weights for each group.

- Note: most writes go through the page cache.
 (So classic writes will appear to be unthrottled at first.)

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Net_cls and net_prio cgroup

- Only works for egress (outgoing) traffic.

- Automatically set traffic class or priority
  for traffic generated by processes in the group.

- Net_cls will assign traffic to a class.

- Classes have to be matched with tc or iptables, otherwise traffic just flows normally.

- Net_prio will assign traffic to a priority.

- Priorities are used by queuing disciplines.

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Devices cgroup

- Controls what the group can do on device nodes

- Permissions include read/write/mknod

- Typical use:

- allow `/dev/{tty,zero,random,null}` ...
  - deny everything else

- A few interesting nodes:

- `/dev/net/tun` (network interface manipulation)
  - `/dev/fuse` (filesystems in user space)
  - `/dev/kvm` (VMs in containers, yay inception!)
  - `/dev/dri` (GPU)

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/Container-Ship-Freighter-Navigation-Elbe-Romance-1782991.jpg)]

---

Namespaces

.nav[
[Previous part](#toc-control-groups)
|
[Back to table of contents](#toc-part-4)
|
[Next part](#toc-security-features)
]

---

# Namespaces

- Provide processes with their own view of the system.

- Namespaces limit what you can see (and therefore, what you can use).

- These namespaces are available in modern kernels:

- pid
  - net
  - mnt
  - uts
  - ipc
  - user
  - time
  - cgroup

(We are going to detail them individually.)

- Each process belongs to one namespace of each type.

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Namespaces are always active

- Namespaces exist even when you don't use containers.

- This is a bit similar to the UID field in UNIX processes:

- all processes have the UID field, even if no user exists on the system

- the field always has a value / the value is always defined
 
 (i.e. any process running on the system has some UID)

- the value of the UID field is used when checking permissions
 
 (the UID field determines which resources the process can access)

- You can replace "UID field" with "namespace" above and it still works!

- In other words: even when you don't use containers,
 there is one namespace of each type, containing all the processes on the system.

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Manipulating namespaces

- Namespaces are created with two methods:

- the `clone()` system call (used when creating new threads and processes),

- the `unshare()` system call.

- The Linux tool `unshare` allows doing that from a shell.

- A new process can re-use none / all / some of the namespaces of its parent.

- It is possible to "enter" a namespace with the `setns()` system call.

- The Linux tool `nsenter` allows doing that from a shell.

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Namespaces lifecycle

- When the last process of a namespace exits, the namespace is destroyed.

- All the associated resources are then removed.

- Namespaces are materialized by pseudo-files in `/proc/<pid>/ns`.

```bash
  ls -l /proc/self/ns
  ```

- It is possible to compare namespaces by checking these files.

(This helps to answer the question, "are these two processes in the same namespace?")

- It is possible to preserve a namespace by bind-mounting its pseudo-file.

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Namespaces can be used independently

- As mentioned in the previous slides:

*A new process can re-use none / all / some of the namespaces of its parent.*

- We are going to use that property in the examples in the next slides.

- We are going to present each type of namespace.

- For each type, we will provide an example using only that namespace.

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## UTS namespace

- gethostname / sethostname

- Allows setting a custom hostname for a container.

- That's (mostly) it!

- Also allows setting the NIS domain.

(If you don't know what a NIS domain is, you don't have to worry about it!)

- If you're wondering: UTS = UNIX time sharing.

- This namespace was named like this because of the `struct utsname`,
 
 which is commonly used to obtain the machine's hostname, architecture, etc.

(The more you know!)

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Creating our first namespace

Let's use `unshare` to create a new process that will have its own UTS namespace:

```bash
$ sudo unshare --uts
```

- We have to use `sudo` for most `unshare` operations.

- We indicate that we want a new uts namespace, and nothing else.

- If we don't specify a program to run, a `$SHELL` is started.

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Demonstrating our uts namespace

In our new "container", check the hostname, change it, and check it:

```bash
 # hostname
 nodeX
 # hostname tupperware
 # hostname
 tupperware
```

In another shell, check that the machine's hostname hasn't changed:

```bash
$ hostname
nodeX
```

Exit the "container" with `exit` or `Ctrl-D`.

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Net namespace overview

- Each network namespace has its own private network stack.

- The network stack includes:

- network interfaces (including `lo`),

- routing table**s** (as in `ip rule` etc.),

- iptables chains and rules,

- sockets (as seen by `ss`, `netstat`).

- You can move a network interface from a network namespace to another:
  ```bash
  ip link set dev eth0 netns PID
  ```

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Net namespace typical use

- Each container is given its own network namespace.

- For each network namespace (i.e. each container), a `veth` pair is created.

(Two `veth` interfaces act as if they were connected with a cross-over cable.)

- One `veth` is moved to the container network namespace (and renamed `eth0`).

- The other `veth` is moved to a bridge on the host (e.g. the `docker0` bridge).

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Creating a network namespace

Start a new process with its own network namespace:

```bash
$ sudo unshare --net
```

See that this new network namespace is unconfigured:

```bash
 # ping 1.1
 connect: Network is unreachable
 # ifconfig
 # ip link ls
 1: lo: <LOOPBACK> mtu 65536 qdisc noop state DOWN mode DEFAULT group default qlen 1000
 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
```

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Creating the `veth` interfaces

In another shell (on the host), create a `veth` pair:

```bash
$ sudo ip link add name in_host type veth peer name in_netns
```

Configure the host side (`in_host`):

```bash
$ sudo ip link set in_host master docker0 up
```

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Moving the `veth` interface

*In the process created by `unshare`,* check the PID of our "network container":

```bash
 # echo $$
 533
```

*On the host*, move the other side (`in_netns`) to the network namespace:

```bash
$ sudo ip link set in_netns netns 533
```

(Make sure to update "533" with the actual PID obtained above!)

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Basic network configuration

Let's set up `lo` (the loopback interface):

```bash
 # ip link set lo up
```

Activate the `veth` interface and rename it to `eth0`:

```bash
 # ip link set in_netns name eth0 up
```

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Allocating IP address and default route

*On the host*, check the address of the Docker bridge:

```bash
$ ip addr ls dev docker0
```

(It could be something like `172.17.0.1`.)

Pick an IP address in the middle of the same subnet, e.g. `172.17.0.99`.

*In the process created by `unshare`,* configure the interface:

```bash
 # ip addr add 172.17.0.99/24 dev eth0
 # ip route add default via 172.17.0.1
```

(Make sure to update the IP addresses if necessary.)

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Validating the setup

Check that we now have connectivity:

```bash
 # ping 1.1
```

Note: we were able to take a shortcut, because Docker is running,
and provides us with a `docker0` bridge and a valid `iptables` setup.

If Docker is not running, you will need to take care of this!

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Cleaning up network namespaces

- Terminate the process created by `unshare` (with `exit` or `Ctrl-D`).

- Since this was the only process in the network namespace, it is destroyed.

- All the interfaces in the network namespace are destroyed.

- When a `veth` interface is destroyed, it also destroys the other half of the pair.

- So we don't have anything else to do to clean up!

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Other ways to use network namespaces

- `--net none` gives an empty network namespace to a container.

(Effectively isolating it completely from the network.)

- `--net host` means "do not containerize the network".

(No network namespace is created; the container uses the host network stack.)

- `--net container` means "reuse the network namespace of another container".

(As a result, both containers share the same interfaces, routes, etc.)

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Mnt namespace

- Processes can have their own root fs (à la chroot).

- Processes can also have "private" mounts. This allows:

- isolating `/tmp` (per user, per service...)

- masking `/proc`, `/sys` (for processes that don't need them)

- mounting remote filesystems or sensitive data,
 but make it visible only for allowed processes

- Mounts can be totally private, or shared.

- At this point, there is no easy way to pass along a mount
  from a namespace to another.

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Setting up a private `/tmp`

Create a new mount namespace:

```bash
$ sudo unshare --mount
```

In that new namespace, mount a brand new `/tmp`:

```bash
 # mount -t tmpfs none /tmp
```

Check the content of `/tmp` in the new namespace, and compare to the host.

The mount is automatically cleaned up when you exit the process.

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## PID namespace

- Processes within a PID namespace only "see" processes
  in the same PID namespace.

- Each PID namespace has its own numbering (starting at 1).

- When PID 1 goes away, the whole namespace is killed.

(When PID 1 goes away on a normal UNIX system, the kernel panics!)

- Those namespaces can be nested.

- A process ends up having multiple PIDs (one per namespace in which it is nested).

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## PID namespace in action

Create a new PID namespace:

```bash
$ sudo unshare --pid --fork
```

(We need the `--fork` flag because the PID namespace is special.)

Check the process tree in the new namespace:

```bash
 # ps faux
```

🤔 Why do we see all the processes?!?

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## PID namespaces and `/proc`

- Tools like `ps` rely on the `/proc` pseudo-filesystem.

- Our new namespace still has access to the original `/proc`.

- Therefore, it still sees host processes.

- But it cannot affect them.

(Try to `kill` a process: you will get `No such process`.)

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## PID namespaces, take 2

- This can be solved by mounting `/proc` in the namespace.

- The `unshare` utility provides a convenience flag, `--mount-proc`.

- This flag will mount `/proc` in the namespace.

- It will also unshare the mount namespace, so that this mount is local.

Try it:

```bash
 $ sudo unshare --pid --fork --mount-proc
 # ps faux
```

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## OK, really, why do we need `--fork`?

*It is not necessary to remember all these details.
 
This is just an illustration of the complexity of namespaces!*

The `unshare` tool calls the `unshare` syscall, then `exec`s the new binary.
 
A process calling `unshare` to create new namespaces is moved to the new namespaces...
 
... Except for the PID namespace.
 
(Because this would change the current PID of the process from X to 1.)

The processes created by the new binary are placed into the new PID namespace.
 
The first one will be PID 1.
 
If PID 1 exits, it is not possible to create additional processes in the namespace.
 
(Attempting to do so will result in `ENOMEM`.)

Without the `--fork` flag, the first command that we execute will be PID 1 ...
 
... And once it exits, we cannot create more processes in the namespace!

Check `man 2 unshare` and `man pid_namespaces` if you want more details.

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## IPC namespace

- Does anybody know about IPC?

- Does anybody *care* about IPC?

- Allows a process (or group of processes) to have own:

- IPC semaphores
  - IPC message queues
  - IPC shared memory

... without risk of conflict with other instances.

- Older versions of PostgreSQL cared about this.

*No demo for that one.*

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## User namespace

- Allows mapping UID/GID; e.g.:

- UID 0→1999 in container C1 is mapped to UID 10000→11999 on host
  - UID 0→1999 in container C2 is mapped to UID 12000→13999 on host
  - etc.

- UID 0 in the container can still perform privileged operations in the container.

(For instance: setting up network interfaces.)

- But outside of the container, it is a non-privileged user.

- It also means that the UID in containers becomes unimportant.

(Just use UID 0 in the container, since it gets squashed to a non-privileged user outside.)

- Ultimately enables better privilege separation in container engines.

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## User namespace challenges

- UID needs to be mapped when passed between processes or kernel subsystems.

- Filesystem permissions and file ownership are more complicated.

.small[(E.g. when the same root filesystem is shared by multiple containers
  running with different UIDs.)]

- With the Docker Engine:

- some feature combinations are not allowed
 
 (e.g. user namespace + host network namespace sharing)

- user namespaces need to be enabled/disabled globally
 
 (when the daemon is started)

- container images are stored separately
 
 (so the first time you toggle user namespaces, you need to re-pull images)

*No demo for that one.*

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Time namespace

- Virtualize time

- Expose a slower/faster clock to some processes

(for e.g. simulation purposes)

- Expose a clock offset to some processes

(simulation, suspend/restore...)

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Cgroup namespace

- Virtualize access to `/proc/<PID>/cgroup`

- Lets containerized processes view their relative cgroup tree

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/ShippingContainerSFBay.jpg)]

---

Security features

.nav[
[Previous part](#toc-namespaces)
|
[Back to table of contents](#toc-part-4)
|
[Next part](#toc-orchestration-an-overview)
]

---

# Security features

- Namespaces and cgroups are not enough to ensure strong security.

- We need extra mechanisms: capabilities, seccomp, LSMs.

- These mechanisms were already used before containers to harden security.

- They can be used together with containers.

- Good container engines will automatically leverage these features.

(So that you don't have to worry about it.)

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Capabilities

- In traditional UNIX, many operations are possible if and only if UID=0 (root).

- Some of these operations are very powerful:

- changing file ownership, accessing all files ...

- Some of these operations deal with system configuration, but can be abused:

- setting up network interfaces, mounting filesystems ...

- Some of these operations are not very dangerous but are needed by servers:

- binding to a port below 1024.

- Capabilities are per-process flags to allow these operations individually.

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Some capabilities

- `CAP_CHOWN`: arbitrarily change file ownership and permissions.

- `CAP_DAC_OVERRIDE`: arbitrarily bypass file ownership and permissions.

- `CAP_NET_ADMIN`: configure network interfaces, iptables rules, etc.

- `CAP_NET_BIND_SERVICE`: bind a port below 1024.

See `man capabilities` for the full list and details.

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Using capabilities

- Container engines will typically drop all "dangerous" capabilities.

- You can then re-enable capabilities on a per-container basis, as needed.

- With the Docker engine: `docker run --cap-add ...`

- If you write your own code to manage capabilities:

- make sure that you understand what each capability does,

- read about *ambient* capabilities as well.

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Seccomp

- Seccomp is secure computing.

- Achieve high level of security by restricting drastically available syscalls.

- Original seccomp only allows `read()`, `write()`, `exit()`, `sigreturn()`.

- The seccomp-bpf extension allows specifying custom filters with BPF rules.

- This allows filtering by syscall, and by parameter.

- BPF code can perform arbitrarily complex checks, quickly, and safely.

- Container engines take care of this so you don't have to.

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

## Linux Security Modules

- The most popular ones are SELinux and AppArmor.

- Red Hat distros generally use SELinux.

- Debian distros (in particular, Ubuntu) generally use AppArmor.

- LSMs add a layer of access control to all process operations.

- Container engines take care of this so you don't have to.

???

:EN:Containers internals
:EN:- Control groups (cgroups)
:EN:- Linux kernel namespaces
:FR:Fonctionnement interne des conteneurs
:FR:- Les "control groups" (cgroups)
:FR:- Les namespaces du noyau Linux

.debug[[containers/Namespaces_Cgroups.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Namespaces_Cgroups.md)]
---

.interstitial[![Image separating from the next part](https://gallant-turing-d0d520.netlify.com/containers/aerial-view-of-containers.jpg)]

---

Orchestration, an overview

.nav[
[Previous part](#toc-security-features)
|
[Back to table of contents](#toc-part-4)
|
[Next part](#toc-)
]

---
# Orchestration, an overview

In this chapter, we will:

* Explain what is orchestration and why we would need it.

* Present (from a high-level perspective) some orchestrators.

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## What's orchestration?

![Joana Carneiro (orchestra conductor)](images/conductor.jpg)

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## What's orchestration?

According to Wikipedia:

*Orchestration describes the __automated__ arrangement,
coordination, and management of complex computer systems,
middleware, and services.*

*[...] orchestration is often discussed in the context of 
__service-oriented architecture__, __virtualization__, provisioning, 
Converged Infrastructure and __dynamic datacenter__ topics.*

What does that really mean?

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## Example 1: dynamic cloud instances

- Q: do we always use 100% of our servers?

- A: obviously not!

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## Example 1: dynamic cloud instances

- Every night, scale down
  
  (by shutting down extraneous replicated instances)

- Every morning, scale up
  
  (by deploying new copies)

- "Pay for what you use"
  
  (i.e. save big $$$ here)

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## Example 1: dynamic cloud instances

How do we implement this?

- Crontab
  
- Autoscaling (save even bigger $$$)

That's *relatively* easy.

Now, how are things for our IAAS provider?

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## Example 2: dynamic datacenter

- Q: what's the #1 cost in a datacenter?

- A: electricity!

- Q: what uses electricity?

- A: servers, obviously

- A: ... and associated cooling

- Q: do we always use 100% of our servers?

- A: obviously not!

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## Example 2: dynamic datacenter

- If only we could turn off unused servers during the night...

- Problem: we can only turn off a server if it's totally empty!
  
  (i.e. all VMs on it are stopped/moved)

- Solution: *migrate* VMs and shutdown empty servers
 
 (e.g. combine two hypervisors with 40% load into 80%+0%,
 and shut down the one at 0%)

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## Example 2: dynamic datacenter

How do we implement this?

- Shut down empty hosts (but keep some spare capacity)

- Start hosts again when capacity gets low

- Ability to "live migrate" VMs
  
  (Xen already did this 10+ years ago)

- Rebalance VMs on a regular basis
  
  - what if a VM is stopped while we move it?
  - should we allow provisioning on hosts involved in a migration?

*Scheduling* becomes more complex.

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## What is scheduling?

According to Wikipedia (again):

*In computing, scheduling is the method by which threads, 
processes or data flows are given access to system resources.*

The scheduler is concerned mainly with:

- throughput (total amount of work done per time unit);
- turnaround time (between submission and completion);
- response time (between submission and start);
- waiting time (between job readiness and execution);
- fairness (appropriate times according to priorities).

In practice, these goals often conflict.

**"Scheduling" = decide which resources to use.**

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## Exercise 1

- You have:

- 5 hypervisors (physical machines)

- Each server has:

- 16 GB RAM, 8 cores, 1 TB disk

- Each week, your team requests:

- one VM with X RAM, Y CPU, Z disk

Scheduling = deciding which hypervisor to use for each VM.

Difficulty: easy!

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## Exercise 2

- You have:

- 1000+ hypervisors (and counting!)

- Each server has different resources:

- 8-500 GB of RAM, 4-64 cores, 1-100 TB disk

- Multiple times a day, a different team asks for:

- up to 50 VMs with different characteristics

Scheduling = deciding which hypervisor to use for each VM.

Difficulty: ???

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## Exercise 2

- You have:

- 1000+ hypervisors (and counting!)

- Each server has different resources:

- 8-500 GB of RAM, 4-64 cores, 1-100 TB disk

- Multiple times a day, a different team asks for:

- up to 50 VMs with different characteristics

Scheduling = deciding which hypervisor to use for each VM.

![Troll face](images/trollface.png)

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## Exercise 3

- You have machines (physical and/or virtual)

- You have containers

- You are trying to put the containers on the machines

- Sounds familiar?

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## Scheduling with one resource

## We can't fit a job of size 6 :(

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## Scheduling with one resource

## ... Now we can!

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## Scheduling with two resources

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## Scheduling with three resources

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## You need to be good at this

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## But also, you must be quick!

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## And be web scale!

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## And think outside (?) of the box!

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## Good luck!

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## TL,DR

* Scheduling with multiple resources (dimensions) is hard.

* Don't expect to solve the problem with a Tiny Shell Script.

* There are literally tons of research papers written on this.

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## But our orchestrator also needs to manage ...

* Network connectivity (or filtering) between containers.

* Load balancing (external and internal).

* Failure recovery (if a node or a whole datacenter fails).

* Rolling out new versions of our applications.

(Canary deployments, blue/green deployments...)

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## Some orchestrators

We are going to present briefly a few orchestrators.

There is no "absolute best" orchestrator.

It depends on:

- your applications,

- your requirements,

- your pre-existing skills...

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## Nomad

- Open Source project by Hashicorp.

- Arbitrary scheduler (not just for containers).

- Great if you want to schedule mixed workloads.

(VMs, containers, processes...)

- Less integration with the rest of the container ecosystem.

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## Mesos

- Open Source project in the Apache Foundation.

- Arbitrary scheduler (not just for containers).

- Two-level scheduler.

- Top-level scheduler acts as a resource broker.

- Second-level schedulers (aka "frameworks") obtain resources from top-level.

- Frameworks implement various strategies.

(Marathon = long running processes; Chronos = run at intervals; ...)

- Commercial offering through DC/OS by Mesosphere.

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## Rancher

- Rancher 1 offered a simple interface for Docker hosts.

- Rancher 2 is a complete management platform for Docker and Kubernetes.

- Technically not an orchestrator, but it's a popular option.

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## Swarm

- Tightly integrated with the Docker Engine.

- Extremely simple to deploy and setup, even in multi-manager (HA) mode.

- Secure by default.

- Strongly opinionated:

- smaller set of features,

- easier to operate.

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---

## Kubernetes

- Open Source project initiated by Google.

- Contributions from many other actors.

- *De facto* standard for container orchestration.

- Many deployment options; some of them very complex.

- Reputation: steep learning curve.

- Reality:

- true, if we try to understand *everything*;

- false, if we focus on what matters.

???

:EN:- Orchestration overview
:FR:- Survol de techniques d'orchestration

.debug[[containers/Orchestration_Overview.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/containers/Orchestration_Overview.md)]
---
class: title, self-paced

Thank you!

.debug[[shared/thankyou.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/shared/thankyou.md)]
---

That's all, folks! Questions?

![end](images/end.jpg)

.debug[[shared/thankyou.md](https://github.com/jpetazzo/container.training/tree/2022-02-enix/slides/shared/thankyou.md)]