T123954 had a lot of discussion about how to set up replication of Kafka topics between datacenters. This ticket continues that discussion while focusing on the Change Propagation use case. The main question to debate here is between A: merged topics in aggregate Kafka clusters (e.g. mediawiki.revision create with data from all datacenters) vs. B: separate topics for all datacentetrs (e.g. eqiad.mediawiki.revision_create).
There may be an edge case where certain failover scenarios will lose messages in A (merged topics).