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Jonas Rosland

Open Source Community Manager at {code} by Dell EMC

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In the past year and a half I’ve seen some really cool things come from people who are passionate about two things: Docker and Raspberry Pi.

There have been contests, showing over 2500 containers running on a RPi 2. We’ve seen some amazing stuff coming out from Hypriot to get up and running with Docker quickly on RPi. And not that long ago, Docker themselves took this more seriously and made Raspbian Jessie an officially supported platform.

For this blog post I’d like to show how you can build your own custom Docker-ready Raspberry Pi image. Why, you ask? Well…

You might want to include some packages that you always manually install. Or change the standard username from pi or pirate. Maybe you want to slim down the standard Raspbian distro to the bare minimums needed.

Whatever the reason, I’m here to provide you with a way to do it :)

Let’s get to it

I’ve created a fork of the official pi-gen repo, which we’ll use to create our images.

To build the images we’ll use a Linux machine, your choice of physical or VM. There’s an excellent Vagrant box that I recommend using together with VirtualBox to make this as simple as possible.

Run the following to get it up and running:

vagrant box add ARTACK/debian-jessie https://atlas.hashicorp.com/ARTACK/boxes/debian-jessie
vagrant init ARTACK/debian-jessie

Optional: Edit the Vagrantfile that got put in your directory and increase the RAM to make everything a little more snappy:

config.vm.provider "virtualbox" do |vb|
#   # Display the VirtualBox GUI when booting the machine
#   vb.gui = true
#
#   # Customize the amount of memory on the VM:
  vb.memory = "2048"
end

Alright, time to start the VM, just run vagrant up and you should see it boot up.

Now you’ll have a barebones Debian Jessie VM up and running, you can connect to it by running vagrant ssh.

We need a few tools and my forked repo to be able to create the image, install and clone them like this:

sudo apt-get update
sudo apt-get install quilt kpartx realpath qemu-user-static debootstrap zerofree pxz zip dosfstools git
git clone https://github.com/jonasrosland/pi-gen

Head into the pi-gen directory and create a new file called config. Within it, add IMG_NAME='Raspbian'. That’s it.

Now we can start the build by issuing sudo ./build.sh. This may take a while. Go get some runts.

You should see the following output:

[email protected]:/tmp$ sudo ./build.sh
[20:38:09] Begin /tmp
[20:38:09] Begin /tmp/stage0
[20:38:09] Begin /tmp/stage0/prerun.sh
... {snip} ...
The following NEW packages will be installed:
  aufs-tools cgroupfs-mount docker-engine git git-man libapparmor1 liberror-perl rsync
... {snip} ...
zip /tmp/deploy/image_2016-11-10-Raspbian-lite.zip /tmp/work/2016-11-10-Raspbian/export-image/2016-11-10-Raspbian-lite.img
  adding: 2016-11-10-Raspbian-lite.img (deflated 77%)
... {snip} ...
[20:43:16] End /tmp/export-image

You now have a shiny new Raspbian Jessie lite image with Docker preinstalled! If you’re running in the Vagrant environment make sure you copy the file to your normal OS before going further:

cp work/2016-11-10-Raspbian/export-image/2016-11-10-Raspbian-lite.img /vagrant/

Now go grab those SD cards and give your Raspberry Pis the Docker experience they deserve :)

Extra points

By now you’re probably wondering what I changed to the official repo to get Docker into the Raspbian image. There were a few other minor tweaks, but the Docker addition was simple; I edited one of the scripts (stage2/01-sys-tweaks/01-run.sh) that run during the build cycle to include adding Docker, and adding the user pi to the docker group.

If you want to edit other packages, users or anything else, head into the stage[0-2] folders (we’re not using stage[3-4]) and remove/add whatever you feel like. It’s yours to build!