elastic search optimal number of masters

Question

We currently have a cluster of 6 data node and one non-data node. Of those, two are currently master eligible. This cluster is on EC2.

What is the optimal number of master nodes, or is there a reason to discriminate at all?

Answer 1

A cluster cannot function without a master node. So, the number of master-eligible nodes depends on your tolerance for losing all master nodes.

It might be also helpful to have an odd number of master-eligible nodes and set discovery.zen.minimum_master_nodes to be larger than half of the number of master eligible nodes in your cluster. This should significantly reduce chances of your cluster going into split-brain condition.

For example, for a cluster with 3 master-eligible nodes, you can set discovery.zen.minimum_master_nodes to 2.