[dinvlad]

I think strong versioning in event-driven arch is a must, to avoid strong coupling. Otherwise, it becomes even worse than "normal" call-driven service arch, because it's already plenty hard to find all of the receivers, and if they don't use strong versioning then it's so easy to break them all with one change in the sender.

[crdrost]

Yeah I would tend to agree! I think there is freedom to do something like semver where you have breaking.nonbreaking.bugfix, which might be less “strong”... But in a world with time travel you tend to get surprised by rollbacks which is why they are always my go-to example. “I only added a field, that's non-breaking” well maybe, but the time reversed thing is deleting a field, are you going to make sure that's safe too?

And I think there's a case to be made for cleaning up handlers for old versions after a certain time in prod of course.