You can assign services to one or more instances in an administrator-managed Oracle RAC database or to server pools in a policy-managed database. If Oracle RAC detects an outage, then Oracle Clusterware isolates the failed component and recovers the dependent components. For services, if the failed component is an instance, then Oracle Clusterware attempts to maintain the cardinality of the service. If the service definition allows for failover and that is necessary to maintain cardinality, then failover occurs.
FAN events can occur at various levels within the Oracle Database architecture and are published through Oracle Notification Service and Oracle Streams Advanced Queuing for backward compatibility with previous OCI clients. FAN callouts can also be written to execute on the database server in response to FAN events.
Note:
Oracle Database does not run Oracle RAC callouts with guaranteed ordering. Callouts are run asynchronously and they are subject to scheduling variability.
FAN is published from a surviving node when the failed node is out of service. The ___location and number of instances in an Oracle RAC environment that provide a service are transparent to applications. Restart and recovery are automatic, including the restarting of the subsystems, such as the listener and the Oracle Automatic Storage Management (Oracle ASM) processes, not just the database. You can use FAN callouts to report faults to your fault management system and to initiate repair jobs.