Update Docker images with Watchtower
After I set up a self-hosted GitHub Actions runner on my Synology NAS, it only worked without issues until a new version of the image had been released. Since I couldn't get automatic updates working with my setup, I settled with a manual update process for the time being. When a reader suggested that I could use Watchtower instead, I decided to try it out when the next version of the runner is released.
Because I was already using Docker Compose for the GitHub Actions runner, I wanted to add Watchtower to the same
docker-compose.yml file to keep everything in one place. I also wanted Watchtower to only update the GitHub Actions runner image and not to interfere with any other containers that might be running in the same Docker instance.
Fortunately, I could find an example in the documentation that fully met these requirements. I didn't need to change much in my existing
docker-compose.yml file to add Watchtower to it:
- I added a Watchtower service to it.
- I set a
com.centurylinklabs.watchtower.scopelabel for the GitHub Actions runner service and then passed its value as
scopeargument in Watchtower's
commandto limit which containers it should monitor and update.
- I disabled the auto update feature for the GitHub Actions runner. It didn't work as expected anyway, but I kept it enabled before to stop the runner when the update failed and in doing that notify me when a manual update was necessary.
This was the resulting
# note: a quirk of docker-in-docker is that this path
# needs to be the same path on host and inside the container,
# docker mgmt cmds run outside of docker but expect the paths from within
command: --scope github-runner
By default, Watchtower checks for new versions of images every 24 hours, which is fine for regular use. I didn't want to wait that long to see if my configuration worked as expected, so I temporarily changed the polling interval by adding the
--interval 30 argument to the Watchtower command in the
docker-compose.yml file above. Once I was done with testing, I removed that argument again.
I'm glad to have learned about Watchtower. It's easy to configure and a great fit for my issue with updating the GitHub Actions runner. I'm certain I'll find use for it in other scenarios in the future.