Cluster: Best Practices
Clusters should have an odd number of at least 3 nodes
We recommend setting up clusters with an odd number of nodes equal to or greater than 3.
A single node cluster:
Will not have the ability to automatically failover to another node if it goes down.
This means that it is not highly available.
A two nodes cluster:
Also not recommended since the cluster must have a consensus among the majority of nodes to operate.
With a two-node cluster, if one of the nodes is down or partitioned, the other node is not considered a 'majority' and thus no Raft command will be created, although any database on the surviving node will still be responsive to the user.
Odd number of 3 or more nodes:
For ACID guarantees, a majority of the nodes must agree on every cluster-wide transaction, so having an odd number of nodes makes achieving the majority easier.
Avoid different cluster configurations among the cluster's nodes
Configuration mismatches tend to cause interaction problems between nodes.
If you must set cluster configurations differently in separate nodes,
we recommend first testing it in a development environment to see that each node interacts properly with the others.