Use docker compose’s `build` directive

[chuck-alt-delete]

In the messaging modernization lab, I notice the user is supposed to do some setup for various jars and build docker images first. Perhaps we could use the docker compose build directive so that docker compose will automatically build those images.

Better yet would be to build and publish those images to dockerhub ourselves so the user doesn’t have to build them locally.

I also notice some connectors being installed on the connect container on startup. Same idea as above — we could bake that into a new docker image instead of requiring that at launch time.

One more thing I notice is the use of depends_on. In my experience, this only actually checks whether a container is running, not whether the service is actually running. This means in some cases, services will fail unpredictably. To solve this, we can use the healthcheck directive. The Confluent docker images come with the cub utility that can be used for a health check. I think cp demo implements this, but I’d have to check.

[chuck-alt-delete]

depends_on actually seems fine here. Cub should just work out if the box for health checks since there’s no extra security plugins needed in this project. So no need for healthcheck.

For reference, CP Demo does this: https://github.com/confluentinc/cp-demo/blob/6.2.1-post/docker-compose.yml#L643

They set CUB_CLASSPATH environment variable. But I think that’s only necessary since they need extra security plugins for rbac and authentication and stuff.