vRealize Automation requires the appliance database for system operation. You can manage the appliance database through the vRealize Appliance Virtual Appliance Management Console (VAMI).
You can configure the database as a single node system or with multiple nodes to facilitate high availability through failover. The appliance database is set up initially when you install the vRealize Automation system, and it requires no maintenance unless a machine configuration changes or, in the case of a clustered system, you need to promote a different node to be the master for some reason.
The database clustered configuration is set up automatically when you join a virtual appliance to the cluster using the Join cluster operation. However, the database cluster is not directly dependent upon the virtual appliance cluster. For instance, a virtual machine joined to a cluster could be operating normally even if the embedded Postgres appliance database is not started or has crashed.
In a clustered configuration, there is a master node and one or more replica nodes. The master node is the vRealize Automation appliance node with the master database that supports system functionality. Replica nodes contain copies of the database that can be pulled into service if the master node fails.
There are several options to configuring a high availability appliance database configuration. The most important consideration is to choose the replication mode for your system. The replication mode determines how your vRealize Automation deployment maintains data integrity and, for high availability configurations, how it fails over should the master or primary node fail. There are two available replication modes: synchronous and asynchronous.
Both replication modes support database failover, though each has advantages and disadvantages. Synchronous mode minimizes the chances of data loss, but at the cost of system performance and the need for more hardware. Synchronous mode also requires at least three nodes. Asynchronous mode is more flexible and affects system performance less at the cost of some increased risk of data loss. vRealize Automation supports both modes, but operates in asynchronous mode by default and provides high availability only if there are at least two appliance database nodes. The Database tab on the Virtual Appliance Management Interface enables you to switch synchronization modes and to add database nodes as needed. If you start with one node in a non-high availability configuration, you can add nodes later as desired to enhance high availability. If you have the appropriate hardware and require maximum protection against data loss, consider configuring your deployment to operate in synchronous mode.