Improve database migrations reliability #4994
Description
Why are we doing this?
Dokku recommends that database migrations are done during deployment but before an app is deployed. They recommend that the migrations are applied during the "release" phase.
We recently had an outage where migrations were not fully applied during a deployment and the app needed to be redeployed in order for the migrations to be applied fully.
We applied the following change in OpenCodelists to address this: opensafely-core/opencodelists#2393 opensafely-core/opencodelists#2736
How will we know when it's done?
Migrations can be successfully applied during the release phase rather than during app start up.
What are we doing?
Moving the application of Django migrations to the Procfile : release and removing them from the entrypoint script that's run on container startup.
Note: we'll need to test this change, either with the same this approach taken for OpenCodelists or the potentially simpler approach using Vagrant taken by Becky.