A Group Change is the event that occurs when a cluster forms a new group. This occurs when a node joins or leaves the cluster group. This can also manifest in Clustrix Insight as 503 Errors while the Group Change occurs.
Transient Node Failure
When the cluster loses contact with an individual node for any reason, remaining nodes in the cluster form a new group without this node and continue serving clients. All services like replication slaves are reassigned across the surviving nodes. Clients connected through a load balancer experience only a short unavailability during a group change. Clients that were distributed to the failed node must reconnect. Clients that were directly connected to the failed node will be unable to query the database and must connect to another node.
After the failed node has recovered, it will rejoin the cluster and accept work. While a failed node may require manual intervention to recover (example: restoring power), no further action is needed to reintegrate a node into the cluster after it is restored.
New Node Addition
When a new node (or nodes) is added to the Cluster, the cluster forms a new group with that node added as a member. At this point the Cluster will begin balancing data to the new node.