Chapter 9 High Availability for FortiOS 5.0 : HA and failover protection : Monitoring cluster units for failover
  
Monitoring cluster units for failover
You can use logging and SNMP to monitor cluster units for failover. Both the primary and subordinate units can be configured to write log messages and send SNMP traps if a failover occurs. You can also log into the cluster web‑based manager and CLI to determine if a failover has occurred. See “Monitoring cluster units for failover”.