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.