Failover is the automatic switch to a standby system when a primary component fails or drops offline. Automation is the defining trait: the cutover happens without a person deciding to pull the lever, which is what separates true failover from a manual switchover. In mission-critical systems the gap between failure and recovery is measured in seconds or milliseconds.
Making it work requires redundant infrastructure that can detect a failure and take over primary duties immediately, whether that is a database cluster, a load-balanced web farm, redundant network links, or cloud availability zones. The mistake teams make is assuming failover works because it was configured. Untested failover fails at the worst moment, when a health check misfires, replication has silently fallen behind, or both nodes try to act as primary at once. Regular, deliberate failover testing is the only way to trust it.
How is failover tested on the CISSP?
Failover appears in Domain 7: Security Operations under high availability and business continuity. Candidates should understand failover within resilient system design and how testing it validates the wider recovery plan. Distinguishing automatic failover from manual switchover and from load balancing is a frequent point of confusion.