Failover is the automatic switching of operation to a standby system, server, or network path when the active component fails or becomes unreachable, minimising service disruption. It is a core mechanism for achieving high availability, typically implemented through health checks, heartbeat monitoring, and standby replicas that can assume traffic within seconds. Failover strategies range from active-passive, where a standby remains idle until needed, to active-active, where multiple nodes share load and absorb failures without a distinct switchover step. Anycast routing achieves failover at the network layer by withdrawing route advertisements for unreachable nodes.