Fair. The most (semi-recent) controversial astronaut I can think of right now might be Martin Fowler and his work on event sourcing + CQRS. I don’t know if he writes code or not, but I’ve heard a lot of angst from the people who have adopted those patterns. I made a small system using those ideas built on AWS Event Bus and it generally worked quite well, but I can see where making that pattern the law in a larger setting could be excruciating.
The system processes a stream of log events and triggers lambda functions that each handle various API calls in a user provisioning flow. Some of the tasks could run independently of the others, and those that depend on successful completion of a prior task are triggered based on a pattern-matched log emitted from the dependent lambda functions. Failure on any of the functions pushes events to a shared dead letter queue. Everything needs to be idempotent and use the original source timestamp field to be handled correctly. We could have achieved the same business logic with Step Functions (or any number of approaches, with the requirement that no new servers had to be managed) but Event Bus had a ready-made integration with an event source that we needed, and was a lot cheaper to operate. I can't really speak in depth to the gripes of others, but I can say that tracing and debugging was hard until we made it easy. If we had to add a lot more interdependent business logic to the system it would have probably become difficult to maintain.
Trying to choreograph dozens of lambda functions is one of those solutions that’s more hype than sense. AWS pitched lambda for one-off video transcoding, then overzealous folks took it way way too far.
FWIW, event driven is not event sourced. AWS Event Bus is neither persistent nor ordered which makes it not fit for event sourcing unless the lambdas were only an ingest for Kinesis or the like. For example: how would consistent replay be accomplished?
It's so easy to shoot yourself in the foot with CQRS...I have yet to see co much duplication in an otherwise clean codebase like I saw in the single CQRS I worked on.
