It depends on what you're doing. On some projects we've put the job queue into our database, which works great at low and medium traffic volumes and means we ca

It depends on what you're doing. On some projects we've put the job queue into our database, which works great at low and medium traffic volumes and means we can do exactly the same thing for external systems if they let us send them an ID. I agree that the first port of call is to make your operation legitimately idempotent without passing IDs around, and the second is to ask if it is really important enough to care about delivery, but if you're not operating at ridiculous scale and you're okay with having a single point of failure then you get to avoid the "distributed systems are hard" rule by not actually having a completely distributed system.