I phrased it poorly, I'm aware that SolrCloud uses replication as needed.
My base question here is are we sure that if a user has a classic master/slave setup and is running SolrCloud, do they play nice together? So a slave polls the master, and new segments are moved to the slave (classic). Meanwhile, the master may or may not be the leader. The updates may have been received already via the leader forwarding the requests. Does this all behave well?
And if the leader goes down, a new leader is elected and classic replication does what?
It seems like the replication handler polling should just be disabled in the SolrCloud world or is this all "just handled" today?
We've seen problems in the past where people configure a classic master/slave setup then merrily index to both machines, replication can get all confused. I'm making sure this has been handled or at least is flagged as something to check.
And, yes, "they shouldn't do that". If we can put in a low-cost way to insure this it might save people grief. And people will no doubt be upgrading from 3.x at some point, moving their solrconfig files if nothing else....
But as I said, I may be seeing something that's not there in which case we can close this as "silly boy is hallucinating again"...