Access Your Version Controlled Configuration from a Docker Container

For years now, I’ve stubbornly duplicated version-controlled configuration files into my running Docker containers. Meaning, instead of making the files accessible directly by the container, I’ve been maintaining both the version-controlled file and copies used by the containers. At last, I’ve found a solution to help avoid the duplication.

The problem

Right now I keep my configuration files in a homelab repository. For example, /home/fletcher/homelab/gatus/config/config.yml has my configuration for my Gatus monitoring. But when I first started running services in 2019, I settled on keeping all service data jailed to /home/fletcher/service-data; for example, service-data/gatus for Gatus data, service-data/home-assistant for Home Assistant data, etc. Keeping all container data compartmentalized to service-data made sense in my brain.

The problem is, for service data that is human-managed configuration, like Gatus, how can I keep it version controlled? I could make it its own git repository, but then it would be decoupled from the rest of my homelab content. I could duplicate it, but who wants that? So I tried symlinks…and failed miserably. I tried symlinking service-data/gatus to homelab/gatus, but since path mappings are different in the container, the symlinks don’t work.

At this point I gave up and duplicated the content, which of course means they sometimes got out of sync.

The solution – duh

The solution was pretty obvious when I slept on it for a few years and took another look. Somehow in my head I got “keep all service data jailed to /home/fletcher/service-data.” But by simply bind mounting another directory, poof, now I can point directly at the source directory! Duh!!!!

An example

Here is what my compose configuration looks like for Gatus:

gatus:
    container_name: gatus
    image: twinproduction/gatus:v5.37.0
    restart: unless-stopped

    networks:
      - gatus
    ports:
      - 8080:8080
    volumes:
      - ${HOMELAB_DIR}/gatus/config/config.yaml:/config/config.yaml:ro
      - ${SERVICE_DATA_DIR}/gatus/data:/data

And then in my .env file I have:

HOMELAB_DIR=/home/fletcher/git/homelab
SERVICE_DATA_DIR=/home/fletcher/service-data

Super straightfoward. In the case of Gatus, there’s no reason for its configuration to be changed by the application, so we bind it read-only.

Conclusion

This is such a blindingly obvious solution I’m embarrassed to be writing about it seven years later. I think I got myself into this pickle because I was too fixated on “all Docker service data must be jailed to /home/fletcher/service-data!” And that constraint had me overlooking other solutions.

But, that said, we all have our blinders on sometimes. This is a good reminder to be patient and empathetic when others have their blinders on, as we’re all human and you’ll likely have yours on again next week.