4 ms·
From what I've learned, running any cluster on fewer than four nodes is not really recommended.
by fnordsensei 8y ago
From what I've learned, running any cluster on fewer than four nodes is not really recommended.
- Xylakant 8y agoI’ve run quite a few cluster on such a configuration or alternatively 3 data/master-eligible nodes. It’s a safe configuration unless you manage to overload the elected master. But if you’re fighting that issue, you’ll have to go beyond 4 nodes and have a triplet of dedicated master-eligible nodes plus whatever data nodes you need. I pretty much specifically avoid 4 node clusters. You’d have to either designate 3 of the four nodes as master-eligibile with a quorum of 2 or have all of them master-eligible with a quorum of 3. Both options allow for failure of a single node before the cluster becomes unavailable. Any other configuration would either fail immediately on a node loss (quorum 4) or be unsafe (quorum of 2, allows for split-brain) I’d much rather opt for 4 data/master eligible nodes plus a dedicated master eligible node with a quorum of 3. You also need to pick the number of replica suitably: each replica allows for the loss of a single random(!) data node while retaining all your data. Note that if losses are not random but you want to safeguard against loss of a rack or an availability zone or such, configurations are possible that distribute primary and replica suitably (“keep a full copy on either side”)