i'm starting getting into elasticsearch cluster, and i have read many time the recomendation to have 3 master eligible nodes to have high availability.
I've also read that if you have dedicated master nodes should not be used for indexing or requests. However if a node if data and master it can, for instance in a 3 node configuration where each node is master/data node you could send requests to any of them.
So first question: whats the difference on being master only node and master/data node? if i should not send requests to a master only node, i thing a master/data node has more work to do than a master only node, so why should i send request to the first and not the later?
My other question is if the following configuration is a valid variation from the 3 node configuration:
node1 Master/data node
node2 Master/data node
node3 Master/data node (voting only)
in this configuration node3 will never act as master, will only participate in voting, i still can loose any of the 3 nodes as soon as there are 2 running, and i could direct requests to node3 as it will never be a master. Is that OK?