I think they have a task worker system built back in 2014[1], so they need to have something custom working with it as well. Back then I think they really didn't have many options, but if they were to do it again now, I think either AWS Lambda or AWS Batch will serve this type of scheduled job cases very well.

[1]: https://engblog.nextdoor.com/nextdoor-taskworker-simple-effi...