I'm looking at the documentation for outscaling search. In particular, the diagram here is interesting.
It's quite possible my understanding is wrong, but it seems to me that you could simply configure the Query Engine settings on your various CM servers all to point to the URL of your "master" search host.
Have I understood the architecture correctly? What added value is there in having slave servers? There's a hint in the documentation for configuring slaves that it might have to do with replication. Do we then have fully automatic replication of the index?