The master and master replica nodes

The master or master replica node is critical to the availability of the vRealize Operations cluster. It contains all vRealize Operations services, including UI, Controller, Analytics, Collector, and Persistence, as well as critical services that cannot be replicated across all cluster nodes. These include the following:

• NTP server
• GemFire locator

During a failure event of the master node, the master replica DB is promoted to a full read/write master. Although the process of replica DB promotion can be done online, the migration of the master role during a failover does require an automated restart of the cluster. As a result, even though it is an automated process, the failure of the master node will result in a temporary outage of the vRealize Operations cluster until all nodes have been restarted against the new master.

The master also has the responsibility for running both an NTP server and client. On initial configuration of the first vRealize Operations node, you are prompted to add an external NTP source for time synchronization. The master node then keeps time with this source, and runs its own NTP server for all data and collector nodes to sync from. This ensures all nodes have the correct time, and only the master/master replica requires access to an external time source.

The final component that is unique to the master role is the GemFire locator. The GemFire locator is a process that tells starting or connecting data nodes where running cluster members are located; this process also provides load balancing of queries that are passed to data nodes that then become data coordinators for that particular query: