Last week Jérôme Petazzoni did an excellent (abbreviated) version of his ‘Deep dive into Docker storage drivers‘ at the London Docker Meetup. If I wasn’t convinced enough by that, Jessie Frazelle hammered home the same point in her QCon Presentation – AUFS is where it used to be at, and the new king is Overlay. I set about trying it out for myself during Jessie’s presentation, and as I couldn’t find a simple guide I’m writing one here.

Update 24 Dec 2015 If you’re using Ubuntu after the switch to systemd (14.10+) then you need these instructions.

3.18 Kernel

OverlayFS has been in Ubuntu kernels for some time, but that’s not what we want. Overlay (without the FS) is a different kernel module, so you’ll need to install the 3.18 (or later) kernel:

cd /tmp/
wget http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.18-vivid/linux-headers-3.18.0-031800-generic_3.18.0-031800.201412071935_amd64.deb
wget http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.18-vivid/linux-headers-3.18.0-031800_3.18.0-031800.201412071935_all.deb
wget http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.18-vivid/linux-image-3.18.0-031800-generic_3.18.0-031800.201412071935_amd64.deb
sudo dpkg -i linux-headers-3.18.0-*.deb linux-image-3.18.0-*.deb

I’ve tested this myself on Ubuntu 14.04 and 12.04.

3.19 Kernel

Thanks to Manbeard for pointing out that the release of 15.04 makes the kernel upgrade much easier:

sudo apt-get install -y –install-recommends linux-generic-lts-vivid

Docker bits

You’ll need Docker 1.4 or later (I tested on 1.5), which can be installed using the usual Ubuntu instructions if you don’t already have it.

After rebooting to get the new kernel it’s now necessary to set ‘-s overlay’ in the DOCKER_OPTS within /etc/default/docker:

# Use DOCKER_OPTS to modify the daemon startup options.
DOCKER_OPTS="-s overlay"

Restart the Docker service, and if all is well you should get the following output from ‘docker info’

$ sudo docker info
Containers: 0
Images: 0
Storage Driver: overlay
 Backing Filesystem: extfs
Execution Driver: native-0.2
Kernel Version: 3.18.0-031800-generic
Operating System: Ubuntu 14.04.1 LTS
etc...

I seem to recall needing ‘modprobe overlay’ on 12.04 to get things working. I’d also note the bad news that Docker falls back to DeviceMapper (rather than AUFS) if it can’t make Overlay work.

Update

[1] Justin Cormack pointed me at this article ‘Another union filesystem approach‘