Due to some limitation with our provisioning system, it is difficult to provision an odd number of nodes.
For some other technologies, we have provisioned zookeepers with an even number of nodes for 2-3 years now and they never ran into split-brain situations.
So I wanted to check if the same can be expected from ES master node clusters too.
Example:
If we have a 6 node master cluster, then does the quorum occur at 3 nodes or 4 nodes ?
I would expect the quorum formula to be: ceil(N/2) as there in zookeeper too. But a confirmation would be much appreciated.
The docs describe the need for a majority of master eligible nodes to be present. Having an even number of nodes in a cluster is not uncommon, although they are typically distributed across 3 availability zones.
To be clear, even with 2 master-eligible nodes there is no risk of split-brain. The worst thing with a cluster with just 2 master-eligible nodes is you lose half-or-more of them (i.e. one) and the cluster stops working until they come back.
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