Add pull option to docker compose build

[lognaturel]

As of getodk/central#428, we pin all base images to minor versions. The goal is for hosters to get patches at time of upgrade.

I considered adding pull for all the sections in https://docs.getodk.org/central-install-digital-ocean/#advanced-configuration-options and https://docs.getodk.org/central-troubleshooting/ The nice thing with that is there would be more opportunities to get point releases. But all of those are rare so it doesn't seem worth possibly adding a confusing setep.

My understanding is that this is what the `--pull` option for `build` does and that `docker compose pull` would not update base images. https://github.com/docker/compose/issues/2742#issuecomment-180077368

[yanokwa]

In my testing, docker compose build --pull didn't update anything, but docker compose pull seemed to update a lot.

I think in Upgrade steps, Step 4, should be..

docker compose pull
docker compose build

This is better than what we have now, and we don't have to put pulling everywhere. I sure would like to understand the difference between the commands though.

[lognaturel]

Maybe docker-compose build --pull --no-cache would be the same as docker compose pull followed by build?

[yanokwa]

Bard says...

docker compose pull: Pulls the images for the services defined in the compose file.

• You might want to use docker compose pull if you are working on a development machine and you want to make sure that you are always using the latest versions of the images for the services that you are developing.

docker compose build --pull: Builds the images for the services defined in the compose file and also pulls any newer versions of the images that are already present on the local machine.

• You might want to use docker compose build --pull if you are deploying a production application and you want to make sure that you are using the latest versions of the images for the services that are running in production.

[yanokwa]

https://www.reddit.com/r/docker/comments/13lz580/comment/jkssd7y/ has more information.

I think we need to do both:

• docker compose pull to update images used in the docker-compose.yml file (e.g., mail)
• docker compose build --pull to update images used in any Dockerfiles (e.g., nginx)