On 2/24/2021 9:04 AM, DAVID MARTIN NIETO wrote:
If I'm not mistaken the number of zookeepers must be odd. Having 3 zoos on 3 different machines, if we temporarily lost one of the three machines, we would have only two running and it would be an even number.Would it be advisable in this case to raise a third party in one of the 2 active machines or with only two zookeepers there would be no blockages in their internal votes?
It does not HAVE to be an odd number. But increasing the total by one doesn't add any additional fault tolerance, and exposes an additional point of failure.
If you have 3 servers, 2 of them have to be running to maintain quorum. If you have 4 servers, 3 of them have to be running for the cluster to be fully operational.
So a 3-server cluster and a 4-server cluster can survive the failure of one machine. This holds true for larger numbers as well -- with 5 servers or with 6 servers, you can lose two and stay fully operational. Having that extra server that makes the total even is just wasteful.
Thanks, Shawn
