"What didn't work out?" -- I've learned in my career that, in general, I really like replayability, …

… "What didn't work out?" -- I've learned in my career that, in general, I really like replayability, so Kafka is typically my first choice, unless I know that re-creating the messages are trivial, in which case I am more inclined to lean toward RabbitMQ or SQS. I've been bitten several times by MQs where I can't easily recreate the queue, and I lose critical messages. "Where did you regret adding complexity?" -- Again, smaller systems that are just "job queues" (versus service-to-service async communication) don't need a whole lot of complexity. So I've learned that if it's a small system, go with an MQ first (any of them are fine), and go with Kafka only if you start scaling beyond a single simple system. "And if you stuck with a DB-based queue -- did it scale?" -- I've done this in the past. It scales until it doesn't. Given my experience with MQs and Kafka, I feel it's a trivial amount of work to set up an MQ/Kafka, and I don't get anything extra by using a DB-based queue. …