[ancieque]

My opinion on this is that if you need at least once semantics it is best to encode this behaviour in a store you can trust, take the ID of the task and then schedule a task with that data.

Then, add a "sweeper" that checks if the task actually happened and if it did not happen, requeue the job.

To ensure proper behaviour that the same job is not being worked on twice, add some locking in there and you have a really stable way of scheduling jobs.

Could this have been done INSIDE celery? Sure, but I would say that this is not the case that it should optimize for.