Cooking with Containers

If you follow my blog you probably already know I’ve been playing around with docker and CoreOS from sometime now. Even though I have several KVM instances of CoreOS running on my home server, I felt the need to have a VM on my mac to learn more stuff on the go.

I’ve spined up a CoreOS vagrant and started having some fun.

Yeah, yeah, I know there’s boot2docker, that abstracts everything in a easy install, so why have all the fuss of getting CoreOS up and running? Because I believe CoreOS will be the building block of the future of containerisation. And the time for learning about it, is now!

I started by building my first docker image from scratch. Things escalated quite quickly and I ended up with an awesome chef cookbook testing setup, almost by accident :p

Hoping you might find my setup useful as it’s been for me, here’s a blog post explaining how to get it up and running.

Software spec

For comparison purposes, these were my software versions when I wrote this post:

Package	Version
Mac OS X	10.9.5
Virtualbox	4.3.18
Vagrant	1.6.5
CoreOS	505.1.0
Docker	1.3.0
ChefDK	0.3.5
test-kitchen	1.2.1
kitchen-docker	1.5.0

Lets get down to business

Download and install the following packages:

• Homebrew
• Virtualbox
• Vagrant
• Chef Development Kit (chefdk)

Install the test-kitchen gem and its docker driver

chef gem install test-kitchen
chef gem install kitchen-docker

Install docker

brew update
brew install docker

Clone CoreOS vagrant config and spin it up

git clone https://github.com/coreos/coreos-vagrant.git
cd coreos-vagrant
vagrant up
vagrant ssh

Enable remote API for docker

By default, CoreOS has the docker API listening on a local socket. As we’re going to manage containers remotely we’ll need to make docker available on a TCP socket (more info about this here).

On the CoreOS box create the following file /etc/systemd/system/docker-tcp.socket and add this:

[Unit]
Description=Docker Socket for the API

[Socket]
ListenStream=2375
BindIPv6Only=both
Service=docker.service

[Install]
WantedBy=sockets.target

Then enable the new socket:

sudo su -
systemctl enable docker-tcp.socket
systemctl stop docker
systemctl start docker-tcp.socket
systemctl start docker

And logout from the CoreOS box.

Adding a friendly name

On your host, add a friendly hostname for your CoreOS instance

sudo echo "172.17.8.101 coreos01" >> /etc/hosts

Export the new docker endpoint and test it out

export DOCKER_HOST=tcp://coreos01:2375
docker ps -a

You should see something like this:

Note: If you can’t reach the coreos guest via 172.17.8.101 it might be related to an overlapping route on your host. You’ll need to add a new route, here’s an example: route -vn add -net 172.17.8.0/24 -interface vboxnet1

That’s it, let the cooking begin

I’ve made available on github an example so you can start testing your setup right away.

git clone https://github.com/kintoandar/cooking_with_containers.git
cd cooking_with_containers
kitchen converge

This will download a docker image I’ve built from the public docker hub, start a new container, push an example cookbook into it, generate a runlist and do a chef-solo run with that runlist, all like magic.

If all went according to plan, you just converged your first container testing an useless cookbook. So give yourself a pat on the back, good job!

Now you can go on and build awesome cookbooks, fully tested on your new shiny setup, enjoy!

Pro-tip: vim + syntastic + rubocop + foodcritic = another #epic combo!