First time with Docker 🐋

2015-10-12T10:45:26+00:00
Maybe you already hear about Docker</a>, this open source application to manage containers. But it’s not very easy to start working with it.
There is only few weeks that I start to understand how it works. So I decided to write an article to list some basics.
Prerequisites
There are multiple ways to install Docker listed in the documentation</a>.
I am working on OSX, so I will be focus on the OSX environment. If you are on Linux just follow the Docker documentation</a>.
You can use Docker Toolbox</a> to install Docker via an installer. But I prefer to do the installation by using command lines as follows.
First we need VirtualBox installed.
We could install it from their website</a> or with Homebrew Cask</a> like this:
$</span> brew</span> cask</span> install</span> virtualbox</span></span></code></pre>
Then install Docker.</p>
$</span> brew</span> install</span> docker</span></span></code></pre>

If you are using MacPorts there are the same packets</a>.

sudo port install docker</code> do the same.</p>
</blockquote>
Docker Machine#</span></a>
</h3>
On Linux we can use Docker directly after its installation. But on OSX we need to install boot2docker</code> to be able to use Docker. It creates a very small Linux VM.</p>
There is two ways to install it. You can follow installation instructions on boot2docker.io</a> or install it via docker-machine</code>.</p>
I prefer to use docker-machine</code> because it allows to install and manage multiple machines (locales and remotes).</p>
So let’s install it.</p>
$</span> brew</span> install</span> docker-machine</span></span></code></pre>
Then we need to create the Docker machine named dev</code> (Docker Machine get started</a>).</p>
$</span> docker-machine</span> create</span> -</span>-driver</span> virtualbox</span> dev</span></span></code></pre>
If we list our machines we have the dev docker machine.</p>
$</span> docker-machine</span> ls</span></span>
NAME</span>   ACTIVE</span>   DRIVER</span>       STATE</span>     URL</span>                         SWARM</span></span>
dev</span>             virtualbox</span>   Running</span>   tcp://192.168.99.100:2376</span></span></code></pre>
But if we try listing the processes we have an error.</p>
$</span> docker</span> ps</span> #</span> list the processes</span></span>
Get</span> http:///var/run/docker.sock/v1.20/containers/json:</span> dial</span> unix</span> /var/run/docker.sock:</span> no</span> such</span> file</span> or</span> directory.</span></span>
*</span> Are you trying to connect to a TLS-enabled daemon without TLS</span>?</span></span>
*</span> Is your docker daemon up and running</span>?</span></span></code></pre>
docker</code> command needs some informations about the host machine to communicate with it and do the jobs we need.
We have to set the env</code> variables with this command.</p>
$</span> eval</span> "</span>$(</span>docker-machine</span> env</span> dev</span>)</span>"</span></span>
$</span> docker</span> ps</span></span>
CONTAINER</span> ID</span>        IMAGE</span>                        COMMAND</span>                CREATED</span>              STATUS</span>              PORTS</span>               NAMES</span></span></code></pre>
We are now ready to create our first Docker container.</p>
Docker with existing images#</span></a>
</h2>
As first example we could use a simple and light image named busybox</code>.</p>
Busybox#</span></a>
</h3>
Busybox</a> is one of the smallest Docker images (less than 5MB). This image contains “common UNIX utilities into a single small executable”.</p>
$</span> docker</span> run</span> -</span>it</span> busybox</span></span></code></pre>
By doing this command we will create a new container from the busybox</code> image. If this is the first time we execute it, it will pull the image first.

And for this image it will open a shell inside. This come from its definition</a>.</p>
When we are into the container we could do what we want. It’s really close to a VM for this part.

But each time we use docker run</code> command, it will create a new container and loose what we did. If we want to use the same container we have to name it with --name</code> option and --detatch</code> the container.</p>
For example:</p>
$</span> docker</span> run</span> -</span>itd</span> -</span>-name=my-busybox</span> busybox</span></span>
3c4eb1117ece13b72647459960f4438f9da1b9445afe56188b19d1492b8c1c61</span></span>
</span>
#</span> And play with 'my-busybox' container</span></span>
$</span> docker</span> exec</span> -</span>it</span> my-busybox</span> ls</span> -</span>la</span></span>
$</span> docker</span> exec</span> -</span>it</span> my-busybox</span> touch</span> index.html</span></span>
$</span> docker</span> exec</span> -</span>it</span> my-busybox</span> ls</span> -</span>la</span></span>
$</span> docker</span> exec</span> -</span>it</span> my-busybox</span> echo</span> hello</span> world</span></span>
$</span> docker</span> exec</span> -</span>it</span> my-busybox</span> sh</span></span></code></pre>
About the docker run</code> options:

-d, --detach=false</code>: Run container in background and print container ID

--name=</code>: Assign a name to the container

-i, --interactive=false</code>: Keep STDIN open even if not attached.

-t, --tty=false</code>: Allocate a pseudo-TTY.</p>
Debian#</span></a>
</h3>
To test something most common. We could do the same with the debian</code> image.</p>
$</span> docker</span> run</span> -</span>it</span> debian</span></span></code></pre>
For debian</code> image it’s similar than the busybox</code> one. But it will open a instance with bash</code> and not sh</code> (debian image definition</a>).</p>
Nginx#</span></a>
</h3>
Now let’s use nginx</code> image. This works a bit different.</p>
$</span> docker</span> run</span> -</span>p</span> 8000:80</span> nginx</span></span></code></pre>
With this command we expose the port 80</code> of the container into the port 8000</code> of docker host.

Just execute one of this two lines in a new terminal to check it.</p>
$</span> curl</span> $(</span>docker-machine</span> ip</span> dev</span>)</span>:8000</span></span>
</span>
#</span> To open in browser (OSX)</span></span>
$</span> open</span> http://</span>$(</span>docker-machine</span> ip</span> dev</span>)</span>:8000</span></span></code></pre>
Nice but could be better by including content!</p>
$</span> docker</span> run</span> -</span>p</span> 8000:80</span> \</span></span>
  -</span>v</span> /path/to/content:/usr/share/nginx/html:ro</span> \</span></span>
  nginx</span></span></code></pre>
If we refresh our brother we now have our folder accessible :)</p>
About the options:

-p, --publish=[]</code>: Publish a container’s port(s) to the host.

-v, --volume=[]</code>: Bind mount a volume.</p>
Explanation of /path/to/content:/usr/share/nginx/html:ro</code>:

/path/to/content</code>: is the local folder to share.

/usr/share/nginx/html</code>: the remote folder.

ro</code>: read-only mode (optional).</p>
Remove old containers#</span></a>
</h2>
Some commands to help us.</p>
$</span> docker</span> ps</span></span>
CONTAINER</span> ID</span>        IMAGE</span>                        COMMAND</span>                CREATED</span>              STATUS</span>              PORTS</span>               NAMES</span></span></code></pre>
We normally have nothing running. But it does not mean that there is 0 containers.</p>
$</span> docker</span> ps</span> -</span>a</span></span>
CONTAINER</span> ID</span>        IMAGE</span>               COMMAND</span>                  CREATED</span>             STATUS</span>                      PORTS</span>               NAMES</span></span>
60477ca46da0</span>        debian</span>              "</span>/bin/bash</span>"</span>              4</span> minutes</span> ago</span>       Exited</span> (0</span>) 4 seconds ago                        boring_morse</span></span>
4e584955af81</span>        nginx</span>               "</span>nginx -g 'daemon off</span>"</span>   5</span> minutes</span> ago</span>       Exited</span> (0</span>) 35 seconds ago                       agitated_mahavira</span></span></code></pre>
There is container exited. The following command will remove containers that not running.</p>
$</span> docker</span> rm</span> $(</span>docker</span> ps</span> -</span>a</span> -</span>q</span>)</span></span></code></pre>Dockerfile, Docker-composer#</span></a>
</h2>
I will talk about Dockerfile</code> file and docker-compose</code> command in a next article.</p>
Conclusion#</span></a>
</h2>
Really interesting tool but it need a new an approach.

For a web application we don’t really have to use and configure a http server. It’s not the job of the application container. But we may have to use a proxy that could be instantiate into a container. And its the proxy server that will redirect the call into the good docker container port.</p>
Nicolas B. - docker

First time with Docker 🐋
