Enabling Replica Set Arbiter nodes

Percona Server for MongoDB replication model is based on elections, when nodes of the Replica Set choose which node becomes the primary node. Elections are the reason to avoid an even number of nodes in the cluster. The cluster should have at least three nodes. Normally, each node stores a complete copy of the data, but there is also a possibility, to reduce disk IO and space used by the database, to add an arbiter node. An arbiter cannot become a primary and does not have a complete copy of the data. The arbiter does have one election vote and can be the odd number for elections. The arbiter does not demand a persistent volume.

Percona Server for MongoDB Operator has the ability to create Replica Set Arbiter nodes if needed. This feature can be configured in the Replica Set section of the deploy/cr.yaml file:

• set arbiter.enabled option to true to allow Arbiter nodes,
• use arbiter.size option to set the desired amount of the Replica Set nodes which should be Arbiter ones instead of containing data.

For example, the following keys in deploy/cr.yaml will create a cluster with 2 data instances and 1 Arbiter:

....
replsets:
  ....
  size: 3
  ....
  arbiter:
    enabled: true
    size: 1
    ....