What an HA group is

High availability groups use virtual IP addresses (VIPs) to provide active-backup access to Gateway Node or Admin Node services.

HA groups maintain virtual IP addresses that are added to the active node in the group. If the active interface becomes unavailable, the virtual IP addresses are moved to another node. This failover process generally takes only a few seconds and is fast enough that client applications should experience little impact and can rely on normal retry behaviors to continue operation.

All interfaces in an HA group must be within the same network subnet. When creating an HA group, you add node interfaces on the Client Network (eth2) or the Grid Network (eth0).

The active interface in an HA group is designated as the Master. All other interfaces are designated as Backup. To view these designations, select Nodes > Node > Overview.
HA Group Master Interface

When creating an HA group, you specify one node to be the preferred Master. The preferred Master hosts the active interface unless a failure occurs that causes the active interface to move to another node. When the failure is resolved, the active interface is automatically moved back to the preferred Master.

Failover can be triggered for any of these reasons:
Note: Failover is not triggered by network failures external to the node that hosts the active interface.
Note: Failover is not triggered by the failure of the CLB service, the Grid Manager service, or the Tenant Manager service.

In an HA group with more than two nodes, the active interface could move to any of the other nodes in the group during failover.