> Edit: In fact there seems to be a self inflicted problem being created here - having the DLQ on a different system, whether it be another instance of Kafka, or Postgres, or what have you, is really just creating another point of failure.
There's a balance. Do you want to have your Kafka cluster provisioned for double your normal event intake rate just in case you have the worst-case failure to produce elsewhere that causes 100% of events to get DLQ'd (since now you've doubled your writes to the shared cluster, which could cause failures to produce to the original topic).
In that sort of system, failing to produce to the original topic is probably what you want to avoid most. If your retention period isn't shorter than your time to recover from an incident like that, then priority 1 is often "make sure the events are recorded so they can be processed later."
IMO a good architecture here cleanly separates transient failures (don't DLQ; retry with backoff, don't advance consumer group) from "permanently cannot process" (DLQ only these), unlike in the linked article. That greatly reduces the odds of "everything is being DLQ'd!" causing cascading failures from overloading seldom-stressed parts of the system. Makes it much easier to keep your DLQ in one place, and you can solve some of the visibility problems from the article from a consumer that puts summary info elsewhere or such. There's still a chance for a bug that results in everything being wrongly rejected, but it makes you potentially much more robust against transient downstream deps having a high blast radius. (One nasty case here is if different messages have wildly different sets of downstream deps, do you want some blocking all the others then? IMO they should then be partitioned in a way so that you can still move forward on the others.)