You need to integrate transaction coordination with replication to ensure that the replication respects transaction atomicity (so that cross-shard queries get a

You need to integrate transaction coordination with replication to ensure that the replication respects transaction atomicity (so that cross-shard queries get all their reads and writes isolated from each other, and rolled back atomically when a txn is aborted). So separating the layers like you do is only possible if there is an XA protocol between the layers. Neither K8s nor Ceph support that.