Hi,

We 've setup a Redis cluster with 3 masters and 3 replicas, all of them distributed in 3 hosts under the following constraints:

  • initial cluster creation was done in such a way that a master and its replica cannot coexist in the same host
  • each hosts runs 2 Redis daemons.

With this setup we cannot end up having a master and a replica in the same node, but we suffer from a different kind of problem; we may end up having 2 masters on the same host, because one replica failed over automatically due to latency and/or other issues. The problem with this situation is obviously that, if we lose such a host with 2 masters, we 're missing a part of the key space which, for us, it's downtime.

Given the shortage of search results on this topic, I 'm wondering what we 've done wrong and nobody has ever questioned/requested an alert or a fixing-tool which could identify this problematic situation and resolve it (but issuing FAILOVER in one of the replicas to end up again with 1-master-1-replica per host). One possible reason is that maybe people are not mixing multiple Redis installations in the same host to avoid this kind of problem, but given the Redis memory requirements, we thought that it would be a waste of resources to have 6 hosts for this setup.

Could you please advise?

Comment From: itamarhaber

Hello @dmandalidis

Rebalancing a cluster, as you've noticed, is done manually or can be automated by an external arbitrator.

Keep in mind that this issue tracker should be used for reporting bugs or proposing improvements to the Redis server. Kindly close this as it is a question. Questions should be directed to the community:

Comment From: dmandalidis

Ah sorry, posted at https://stackoverflow.com/questions/59600467/redis-cluster-misalignment.

Thans