Brief notes on migrating to Postgres-backed jobs
It seems premature to talk about a migration that is only halfway done, even if it's the hard half that's done — but I think there's something useful in documenting the why and how of a transition while you're still in the thick of it, before the revisionist history of completion sets in.
Early last year, we built out a system for running background jobs directly against Postgres within Django. This very quickly got abstracted out into a generic task runner — shout out to Brandur and many other people who have been beating this drum for a while. And as far as I can tell, this concept of shifting away from Redis and other less-durable caches for job infrastructure is regaining steam on the Rails side of the ecosystem, too.
The reason we did it was mostly for ergonomics around graceful batch processing. It is significantly easier to write a poller in Django for stuff backed by the ORM than it is to try and extend RQ or any of the other task runner options that are Redis-friendly. Django gives you migrations, querysets, admin visibility, transactional guarantees — all for free, all without another moving part.
And as we started using it and it proved stable, we slowly moved more and more things over to it. At the time of this writing, around half of our jobs by quantity — which represent around two-thirds by overall volume — have been migrated over from RQ onto this system.
This is slightly ironic given that we also last year released django-rq-cron, a library that, if I have my druthers, we will no longer need. Fewer moving parts is the watchword. We're removing spindles from the system and getting closer and closer to a simple, portable, and legible stack of infrastructure.