I have elasticsearch setup and working with 2 nodes, everything works great. However if I shut down the master (and the 2nd node takes over as master) -- the enhanced search doesn't recognize the new master. I'm new to this but I assume there needs to be a way to specify multiple elasticsearch servers so in case the master goes down, the other node takes over.
I don't see the ability to enter multiple ES servers in the search options...
How does XenForo need to be setup to have redundant elasticsearch service?
The failover would have to happen outside of XenForo. Elasticsearch is built entirely over HTTP, so essentially you could handle high availability with any sort of HTTP proxy. (You can actually use elasticsearch itself on localhost, assuming you're not using that already, and have that effectively be a proxy with node.client enabled).