Install Discourse and Docker on Ubuntu 14.04 with aufs enabled

While working to run Discourse on Docker I was getting numerous errors about a mount problem related to device mapper.

If you are using Ubuntu 14.04 LTS, want to solve the problem with aufs, and use Salt Stack to control your VMs, here’s how I did it.

After digging for some time, I found others who had also problems to run Discourse in Docker, and that we had to use “aufs”.

I had no idea that we could use different mount subsystems in Docker.

So I had to read some more on we can find out if we have aufs (whatever this is), and that we can tell whether or not Docker is configured to use it.

The issue docker/docker#10161 had proven very helpful to figure out what was my problem. I never thought I could tell Docker to use another device mapper engine anyway. In the end, all you can do is to add a -s foo and it can change the Storage engine.

Turns out that aufs is a Kernel module, and that latest Ubuntu 14.04 has it but not in the default kernel package. You have to make sure that linux-image-extra-virtual and aufs-tools are installed.

Documentation and notes recommends to download and run a shell script to install Docker instead of using the distribution packages. But I refuse to follow this advice because I already manage via Salt stack every components of the infrastructure. I just needed to put the right pieces together.

Since those changes are specific to Discourse I didn’t wanted to make a pull request to saltstack-formulas/docker-formula right away, i’d need to follow Salt formula conventions and add more logic for my PR to be usable by other server runtime too. Not something I had in my plans today.


On the salt master, make sure you have the following:

  1. Add saltstack-formulas/docker-forumla in your gitfs entries

    # /etc/salt/master.d/gitfs.conf
      - roots
      - git
  2. Ensure you have docker in your base top file

    # /srv/salt/top.sls
        - discourse
  3. Create add those lines in /srv/salt/discourse/init.sls

    {% set kernelrelease = salt['grains.get']('kernelrelease') -%}
    {%- set dir = '/srv/webplatform/discourse' -%}
      - docker
        - contents: |
            # Docker Upstart and SysVinit configuration file
            # Managed by Salt Stack, at {{ source }}. Do NOT edit manually!
            # Docker dependencies: Refer to the script at
            # Available cli options:
            DOCKER_OPTS="--dns -s aufs"
        - watch_in:
          - service: docker-service
        - require:
          - pkg: lxc-docker
          - pkg: linux-kernel-deps
        - pkgs:
          - linux-image-extra-{{ kernelrelease }}
          - aufs-tools
        - name: modprobe aufs
        - unless: modinfo aufs > /dev/null 2>&1
        - name: git
        - name:
        - user: ubuntu
        - target: {{ dir }}
        - unless: test -f {{ dir }}/containers/app.yml
        - require:
          - file: {{ dir }}
          - pkg: git
        - name: {{ dir }}
        - user: ubuntu
        - group: ubuntu
        - recurse:
          - user
          - group
  4. Restart your salt master service, sync everything and run highstate

    service salt-master restart
    salt \* saltutil.sync_all
    salt \* service.restart salt-minion
    salt discourse-backend\* state.highstate
  5. Go to the VM and run the installer

    Note that as long as there is no /srv/webplatform/discourse/containers/app.yml the states will update the git repository to the latest version. In my projects, I make sure that salt also generates a configuration file with my current environment details (e.g. DNS, Salt master, Redis, SMTP relay, Postgres’ private IP addresses).