An EDB Postgres Failover Manager (EFM) cluster is comprised of Failover Manager processes that reside on the following hosts on a network:
• Traditionally, a cluster is a single instance of Postgres managing multiple databases. In this document, the term cluster refers to a Failover Manager cluster. A Failover Manager cluster consists of a Master agent, one or more Standby agents, and an optional Witness agent that reside on servers in a cloud or on a traditional network and communicate using the JGroups toolkit.When a non-witness agent starts, it connects to the local database and checks the state of the database:In the event of a failover, Failover Manager attempts to ensure that the promoted standby is the most up-to-date standby in the cluster; please note that data loss is possible if the standby node is not in sync with the master node.JGroups provides technology that allows Failover Manager to create clusters whose member nodes can communicate with each other and detect node failures. For more information about JGroups, visit the official project site at:Figure 2.1 illustrates a Failover Manager cluster that employs a virtual IP address. You can use a load balancer in place of a virtual IP address if you provide your own fencing script to re-configure the load balancer in the event of a failure. For more information about using Failover Manager with a virtual IP address, see Section 3.6. For more information about using a fencing script, see Section 3.5.1.