ADR 0040 — Backup schedules are periodic tasks

Status: accepted

Decision

FairDM’s database and media backups run as two django-celery-beat periodic tasks. After every migration, a post_migrate receiver creates each one, weekly on Sunday at 03:00 in the portal’s time zone, but only when no task of that name exists. A task that exists is never changed. No setting or environment variable decides when a backup runs.

Why

A portal developer changes, disables or runs a backup in the periodic task admin, which django-celery-beat already provides. If a setting could also decide a schedule, there would be two places a schedule comes from, and a deployment could undo a change made in the admin. Creating a task only when it is missing gives every portal backups with no configuration, and keeps each developer’s changes through every later deployment.

The cost is that a deleted task comes back with its default schedule at the next migration. Disabling a task is the supported way to stop a backup.

Revisit if

A portal needs backups on a deployment that runs no Celery beat.