You ingest the log partition in all machines to reconstruct the state from the log. You do this even on the machine that writes to the log, treating the log as the source of truth. Since every user would belong to one partition there would be a globally agreed ordering of their events in the log.
Basically though that makes a CP tradeoff, since a network partition that hides the primary kafka replica from some of the writers causes writes to fail.
There’s simply no way to have a globally distributed system that’s always available and always consistent, either you get inconsistency or you drop writes.
