A Docker primer – from zero to a running Django app
Let’s create a docker container and run a basic Django app - step by step.
Docker is a great tool for creating and managing lightweight isolated application environments, a.k.a. containers. Docker is a wonderful layer on top of Linux containers (LXC). If you’re not familiar with Linux containers, the easiest way to think of them is like extremely lightweight VMs – they allow Linux operating systems to host other copies of Linux, safely sharing access to resources without the overheard of something like Xen or VirtualBox.
Let’s get started!
If you’re already using linux, you can skip the next part, but on OS X, you need to run docker using a Virtualbox linux image at this point.
Installing Vagrant (only neccessary for non-Linux hosts)
Vagrantfile:
Vagrant.configure("2") do|config| config.vm.box = "raring" config.vm.box_url = "http://cloud-images.ubuntu.com/raring/current/raring-server-cloudimg-vagrant-amd64-disk1.box" # we'll forward the port 8000 from the VM to the port 8000 on the host (OS X) config.vm.network :forwarded_port, host:8000, guest:8000 config.vm.synced_folder("vagrant-docker", "/vagrant")
# add a bit more memory, it never hurts. It's VM specific and we're using Virtualbox here. config.vm.provider :virtualboxdo|vb| vb.customize ["modifyvm", :id, "--memory", 2048] end end
Create the shared folder
mkdir vagrant-docker
Boot up the VM with Vagrant
☯ ~/Devel/Own/docker-deploy-blogpost $ vagrant up Bringing machine 'default' up with 'virtualbox' provider... [default] Importing base box 'raring'... [default] Matching MAC address for NAT networking... [default] Setting the name of the VM... [default] Clearing any previously set forwarded ports... [default] Creating shared folders metadata... [default] Clearing any previously set network interfaces... [default] Preparing network interfaces based on configuration... [default] Forwarding ports... [default] -- 22 => 2222 (adapter 1) [default] -- 8000 => 8000 (adapter 1) [default] Running 'pre-boot' VM customizations... [default] Booting VM... [default] Waiting for VM to boot. This can take a few minutes. [default] VM booted and ready for use! [default] Mounting shared folders... [default] -- /vagrant ☯ ~/Devel/Own/docker-deploy-blogpost $
vagrant@vagrant-ubuntu-raring-64:~$ sudo sh -c "wget -qO- https://get.docker.io/gpg | apt-key add -" vagrant@vagrant-ubuntu-raring-64:~$ sudo sh -c "echo deb http://get.docker.io/ubuntu docker main > /etc/apt/sources.list.d/docker.list" vagrant@vagrant-ubuntu-raring-64:~$ sudo apt-get update vagrant@vagrant-ubuntu-raring-64:~$ sudo apt-get install lxc-docker
Getting to know Docker a bit
Now that we have Docker installed and ready to roll, let’s look at some basic commands. The official Docker ‘getting started’ guide is the real deal, go ahead and read it.
vagrant@vagrant-ubuntu-raring-64:~$ sudo docker run ubuntu /bin/echo hello there, docker user hello there, docker user
# curious about the platform this container has? vagrant@vagrant-ubuntu-raring-64:~$ sudo docker run ubuntu uname -a Linux cf95ac04d25d 3.8.0-29-generic #42-Ubuntu SMP Tue Aug 13 19:40:39 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux { # now see the host's uname vagrant@vagrant-ubuntu-raring-64:~$ uname -a Linux vagrant-ubuntu-raring-64 3.8.0-29-generic #42-Ubuntu SMP Tue Aug 13 19:40:39 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux
The first echo was run in the docker container, as the second example shows, see it has a different uname string than the host, though very similar (kernel and architecture).
To see what images are available locally, use:
vagrant@vagrant-ubuntu-raring-64:~$ sudo docker images REPOSITORY TAG ID CREATED SIZE ubuntu 12.04 8dbd9e392a96 4 months ago 131.5 MB (virtual 131.5 MB) ubuntu 12.10 b750fe79269d 5 months ago 24.65 kB (virtual 180.1 MB) ubuntu latest 8dbd9e392a96 4 months ago 131.5 MB (virtual 131.5 MB) ubuntu precise 8dbd9e392a96 4 months ago 131.5 MB (virtual 131.5 MB) ubuntu quantal b750fe79269d 5 months ago 24.65 kB (virtual 180.1 MB)
As you can see, the base ubuntu image includes multiple versions.
Now, you might ask why do I always have to sudo? Well, in the previous versions of docker dockerd used to listen on an HTTP port (4243), but now it uses a socket file:
vagrant@vagrant-ubuntu-raring-64:~$ ls -lah /var/run/docker.sock srw-rw---- 1 root root 0 Aug 30 10:48 /var/run/docker.sock
If you look at the access rights, it’s only usable from the root group. This is actually not a bad thing, but you can add a docker group (docker will automatically use this if available):
# create the 'docker' group vagrant@vagrant-ubuntu-raring-64:~$ sudo groupadd docker # add your user to the 'docker' group vagrant@vagrant-ubuntu-raring-64:~$ sudo gpasswd -a vagrant docker Adding user vagrant to group docker # restart docker so it uses the 'docker' group vagrant@vagrant-ubuntu-raring-64:~$ sudo service docker restart docker stop/waiting docker start/running, process 12032 vagrant@vagrant-ubuntu-raring-64:~$ ls -lah /var/run/docker.sock srw-rw---- 1 root docker 0 Aug 30 11:19 /var/run/docker.sock # now you have to relogin for the group setting on your user to be active. After that you can go without sudo: vagrant@vagrant-ubuntu-raring-64:~$ docker images REPOSITORY TAG ID CREATED SIZE ubuntu 12.04 8dbd9e392a96 4 months ago 131.5 MB (virtual 131.5 MB) ubuntu 12.10 b750fe79269d 5 months ago 24.65 kB (virtual 180.1 MB) ubuntu latest 8dbd9e392a96 4 months ago 131.5 MB (virtual 131.5 MB) ubuntu precise 8dbd9e392a96 4 months ago 131.5 MB (virtual 131.5 MB) ubuntu quantal b750fe79269d 5 months ago 24.65 kB (virtual 180.1 MB)
Let’s run something more useful, a very basic daemon
# run a process which echoes 'hello world' in every second CONTAINER_ID=$(sudo docker run -d ubuntu /bin/sh -c "while true; do echo hello world; sleep 1; done")
Whoa. Let’s see all the details:
CONTAINER_ID : store the container’s id in this shell variable so that it’ll be easier to reference later docker run -d : tell docker to run as a daemon Let’s look at the logs of the container
vagrant@vagrant-ubuntu-raring-64:~$ docker logs $CONTAINER_ID | head hello world hello world hello world
Let’s list the running containers
vagrant@vagrant-ubuntu-raring-64:~$ docker ps ID IMAGE COMMAND CREATED STATUS PORTS 8a5de93a93a8 ubuntu:12.04 /bin/sh -c while tru 4 minutes ago Up 4 minutes vagrant@vagrant-ubuntu-raring-64:~$ echo$CONTAINER_ID 8a5de93a93a8
Aha, there we are with our id. We can attach the console to the container:
vagrant@vagrant-ubuntu-raring-64:~$ docker attach $CONTAINER_ID hello world hello world hello world hello world hello world hello world ^Cvagrant@vagrant-ubuntu-raring-64:~$
And of course we can stop the container.
vagrant@vagrant-ubuntu-raring-64:~$ docker stop $CONTAINER_ID 8a5de93a93a8 vagrant@vagrant-ubuntu-raring-64:~$ docker ps ID IMAGE COMMAND CREATED STATUS PORTS vagrant@vagrant-ubuntu-raring-64:~$
A basic django app on Docker
Let’s run a new container with an interactive console
vagrant@vagrant-ubuntu-raring-64:~$ DJANGO_APP=$(sudo docker run -d -i -t -p 8000:8000 ubuntu /bin/bash) vagrant@vagrant-ubuntu-raring-64:~$ docker ps ID IMAGE COMMAND CREATED STATUS PORTS 3623418e0f85 ubuntu:12.04 /bin/bash 5 seconds ago Up 4 seconds 8000->8000
# now let's attach to it vagrant@vagrant-ubuntu-raring-64:~$ docker attach $DJANGO_APP root@807f3eb43b5c:/#
What’s -i, -t and? See the official docs. (hint: these help running the container in the background)
-p 8000:8000 tells docker to forward port 8000 of the container to port 8000 of the host (Yes, this is a double-forward if you’re using Virtualbox).
Add some extra repos to sources.list and install pip
root@2f6a9bcda315:/# cat > /etc/apt/sources.list deb http://archive.ubuntu.com/ubuntu precise main universe multiverse root@2f6a9bcda315:/# apt-get update . . . root@2f6a9bcda315:/# apt-get install python-pip Use pip to install Virtualenv
warning: no files found matching '*.egg' under directory 'virtualenv_support' warning: no previously-included files matching '*' found under directory 'docs/_templates' warning: no previously-included files matching '*' found under directory 'docs/_build' Installing collected packages: virtualenv Running setup.py install for virtualenv
warning: no files found matching '*.egg' under directory 'virtualenv_support' warning: no previously-included files matching '*' found under directory 'docs/_templates' warning: no previously-included files matching '*' found under directory 'docs/_build' Installing virtualenv script to /usr/local/bin Installing virtualenv-2.7 script to /usr/local/bin Successfully installed virtualenv Cleaning up... root@2f6a9bcda315:/#
Create a basic Django app (I assume you know your way around Django and Python in general)
0 errors found August 30, 2013 - 07:02:46 Django version 1.5.2, using settings 'docker_django.settings' Development server is running at http://0.0.0.0:8000/ Quit the server with CONTROL-C.
Now if you load ‘http://localhost:8000/' in your browser on the host OS, you should see the Django welcome page.
I hope this primer was useful to you. Please share your thoughts as comments and don’t forget to share & like the post! Thank you for your attention.
