This is not specific to Django, but to any project using a database. Here's a list of a couple quite useful resources I used when we had to address this:

* https://github.com/tbicr/django-pg-zero-downtime-migrations

* https://docs.gitlab.com/development/migration_style_guide/

* https://pankrat.github.io/2015/django-migrations-without-dow...

* https://www.caktusgroup.com/blog/2021/05/25/django-migration...

* https://openedx.atlassian.net/wiki/spaces/AC/pages/23003228/...

Generally it's also advisable to set a statement timeout for migrations otherwise you can end up with unintended downtime -- ALTER TABLE operations very often require ACCESS EXCLUSIVE lock, and if you're migrating a table that already has an e.g. very long SELECT operation from a background task on it, all other SELECTs will queue up behind the migration and cause request timeouts.

There are some cases you can work around this limitation by manually composing operations that require less strict locks, but in our case, it was much simpler to just make sure all Celery workers were stopped during migrations.