Move migrations to init container

[sergei-maertens]

Since we're deploying on Kubernetes, we're making use of liveness and readiness probes. If these probes fail too often, the container is deemed unhealthy and is restarted.

Sometimes we have long-running data migrations, which are executed as part of the regular migrate step in the docker command script. These can run so long that the liveness probes fail so often, resulting in a container being restarted. If this happens over and over again, it can mean that the new version/container is never coming up.

One way to deal with this, would be to use the same container image in an init container which only runs the migrations. These containers don't have the "time restriction" that the "main" containers have.

No code changes are particularly needed for this, except for maybe a script/entrypoint similar to bin/docker_start.sh which stops at running the migrations, so we can adapt the infrastructure to that.

[damm89]

@jordi-t heb jij enig idee hoe relevant dit nog is?

[jordi-t]

@damm89 It's indeed good practice to run the migrations from an init-container. This is currently not the case, which in practice means that you'll bump into the issue described by Sergei when your migrations + application start-up run longer than 55 seconds.