Docker : manage LXC containers easily with advanced features

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Docker

Software version 0.11.1
Operating System Debian 8
Website Docker Website
Last Update 09/07/2014
Others

1 Introduction

Docker[1] is an open-source engine that automates the deployment of any application as a lightweight, portable, self-sufficient container that will run virtually anywhere.

Docker containers can encapsulate any payload, and will run consistently on and between virtually any server. The same container that a developer builds and tests on a laptop will run at scale, in production*, on VMs, bare-metal servers, OpenStack clusters, public instances, or combinations of the above.

Common use cases for Docker include:

  • Automating the packaging and deployment of applications
  • Creation of lightweight, private PAAS environments
  • Automated testing and continuous integration/deployment
  • Deploying and scaling web apps, databases and backend services

In short, Docker needs a kernel version 3.8 or above to get AUFS support. This is needed for version < 0.7 as it uses AUFS. In 0.7 version AUFS support will be replaced by Device Mappers to avoid having a recent Linux kernel version.

2 Installation

The problem on Debian with the package, is there is an already existing package called docker. That's why you need to install docker.io:

Command aptitude
aptitude install docker.io lxc

And to make it simpler, set an alias or create a symlink from 'docker.io' to 'docker'.

If you want the latest version, this this a single binary:

Command
wget https://get.docker.io/builds/Linux/x86_64/docker-latest -O /usr/bin/docker
chmod 755 /usr/bin/docker

3 Configuration

3.1 LXC

We will need to make some change regarding the boot of the machine to enable memory managment in the containers by adding 'cgroup_enable' and 'swapaccount' parameters:

Configuration File /etc/default/grub
GRUB_CMDLINE_LINUX_DEFAULT="quiet cgroup_enable=memory swapaccount=1"

Then update grub and reboot your machine:

Command update-grub
update-grub
reboot

3.2 Docker

If you want to change the destination directory where dockers containers will be stored, you simply can use -g option. If you installed with the package, you can modify that parameter here:

Configuration File /etc/default/docker.io
[...]
DOCKER_OPTS="-g /home/pmavro/.docker"
[...]

Here, I can see the folder where I store my docker images and containers.

4 Usage

Now you're ready for the usage. We'll see here the basics and some interesting usages.

4.1 Get images

The first things to do is to get the wanted images you want to work with:

Command
docker pull debian
docker pull ubuntu
docker pull centos

Here I download Centos and Debian.

4.2 List images

You can now list available images like that:

Command docker
> docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             VIRTUAL SIZE
debian              latest              e565fbbc6033        4 weeks ago         115 MB
debian              7.4                 e565fbbc6033        4 weeks ago         115 MB
debian              wheezy              e565fbbc6033        4 weeks ago         115 MB
debian              6.0.9               bc3c71bec50b        4 weeks ago         112.3 MB
debian              squeeze             bc3c71bec50b        4 weeks ago         112.3 MB
debian              jessie              4bd7c3e53dc0        4 weeks ago         120.9 MB
debian              testing             ecd2aa2561ea        4 weeks ago         120.9 MB
debian              sid                 1cda8535c670        4 weeks ago         122.7 MB
debian              oldstable           2cdcb7d79857        4 weeks ago         112.4 MB
debian              experimental        df8f36b7b798        4 weeks ago         159.2 MB
debian              rc-buggy            85f0637e82fc        4 weeks ago         159.2 MB
debian              unstable            e5c43625d004        4 weeks ago         122.7 MB
centos              centos6             0b443ba03958        5 weeks ago         297.6 MB
centos              latest              0b443ba03958        5 weeks ago         297.6 MB
debian              stable              d8309758b8fe        6 weeks ago         115 MB
debian              6.0.8               d56191e18d6b        3 months ago        113.1 MB
debian              7.3                 b5fe16f2ccba        3 months ago        117.7 MB
centos              6.4                 539c0211cd76        13 months ago       300.6 MB
[...]

4.3 Launch a container

When you want to start a container:

Command docker
> docker run -i -t debian bash
[email protected]:/# exit

  • -i: Keep STDIN open
  • -t: Allocate a psuedo-TTY

You can exit a container with exit.

4.4 List containers

You can list running containers:

Command docker
> docker ps
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES

And to list running and stopped containers:

Command docker
> docker ps -a
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS                     PORTS               NAMES
509d83d55238        debian:7.4          /bin/bash           3 minutes ago       Exited (0) 3 minutes ago                       distracted_lalande

4.5 Start container

If a container is stopped, you can easily start it with container ID:

Command docker
> docker start 509d83d55238
509d83d55238

Then you can see it:

Command
> docker ps                
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES
509d83d55238        debian:7.4          /bin/bash           5 minutes ago       Up 5 seconds                            distracted_lalande

4.6 Connect to a container

To connect to a started container, you need to attach to it:

Command docker
> docker attach 509d83d55238
[email protected]:/#

4.7 Commit changes

Now comes interesting things. You can commit changes you've made on a container. That will help you to easily roll back changes for example. So let's install vim or anything to make changes and then commit:

Command docker
> docker commit 509d83d55238 deimosfr/tests
48d436fd27903337c79fca6738f7702ea0eec4304fd0cbd5ebea95854bc9f94e

  • 509d83d55238: the container ID on which you want to commit (get it with 'docker ps -a' command)
  • deimosfr/tests: the name of the commit

Now if you look at the current available images, you'll see your new one:

Command
> docker images 
REPOSITORY          TAG                 IMAGE ID            CREATED             VIRTUAL SIZE
deimosfr/tests      latest              48d436fd2790        2 minutes ago       170 MB

4.8 Diff changes

You can see a diff between a commited version and the changes you've made like that:

Command docker
> docker diff 509d83d55238
A /etc/alternatives/vi
A /etc/vim
A /etc/vim/vimrc
C /usr
C /usr/bin
A /usr/bin/editor
A /usr/bin/vi
A /usr/bin/view
A /usr/bin/vim
A /usr/bin/vim.basic
A /usr/share/bug/vim/script
A /usr/share/doc/vim
[...]

5 References

  1. ^ http://www.docker.io/learn_more/