The replication docs state
a single in-sync copy is sufficient to serve read requests
and then, when describing the read model, the same doc states that the basic flow
Select[s] an active copy of each relevant shard
This suggests that in-sync copies and active copies are the same thing.
But this blog post states
one of the active replicas, which is also in the in-sync set
which clearly implies that there is a difference between the two.
Confusing matters (for me at least) is the
wait_for_active_shards param on the Index API, which makes no reference to in-sync copies.
Are active copies and in-sync copies the same thing? If not, could you please clarify the difference?