From what I understand, when indexing a document in a replicated index, the action returns success only after getting ack from the replicas.
I have an index with 1 shard and 2 replicas.
Each indexing operation is returned only after the 2 replicas sent ack?
If so, can it be changed to majority? So I can get ack from 1 replica and return success?
Yes.
No. The primary waits for ACK from all replicas available at the start of replication before ACKing the client and this is not tunable.