No, you’re misunderstanding the setup. Each replica has a complete
index. Updates get automatically forwarded to _both_ nodes for a
particular shard. So, when a doc comes in to be indexed, it gets
sent to the leader for, say, shard1. From there:
1> it gets indexed on the leader
2> it gets forwarded to the replica(s) where it gets indexed locally.
Each replica has a complete index (for that shard).
There is no master/slave setup any more. And you do
_not_ have to configure replication.