Back up local database before `migrate` in development

[albertas-jn]

After migrate, the local database might become incompatible with other branches. We should automatically back up the existing local database so that we could switch between databases when switching branches.

Related to / blocked by

• 893

[BeritJanssen]

Perhaps this approach could be useful: Docker Backup. This might also be used to address #121 .

[albertas-jn]

@Evert-R Can this issue be closed?

[BeritJanssen]

I tried the following approaches:

• making use of pg_dump: since we don't have information on the migrations, we just dump every time docker-compose up is run. Problematic because a command in the Dockerfile doesn't wait for the start up of Postgres to be complete. Potential solution: use some wait-for-it entrypoint (i.e,. healthcheck & dump rolled into one bash script)
• making use of the dumpdata management command. Advantage: can use something along those lines: python manage.py migrate --check | if [$PIPESTATUS[0] > 0] ; then python manage.py dumpdata -o wherever/we/want/the/backup.dmp; fi, so only run a backup if there are unapplied migrations. Disadvantage: dumpdatawill exit as well if the migrations haven't been applied, as it relies on Django's model state.

So the solution is probably going to be an uninformed pg_dump on every startup (potentially, this could be just a latest.dmp to avoid bloating the backup volume over time), using a custom shell script to await that Postgres is available.