failovers

Failover refers to the process of automatically switching to a redundant or standby component, system, or network upon the failure or abnormal degradation of the primary resource, in order to maintain service availability. It is a key component of high-availability design in information technology and communications infrastructure.

Failover can involve different configurations, most commonly active-passive and active-active deployments. In active-passive setups the standby component remains idle until the primary fails, while in active-active systems multiple units operate simultaneously and share load, with one acting as a hot spare if another fails. Standby resources may be hot (fully operational) or warm or cold (requiring start-up or data synchronization).

Core mechanisms include continuous monitoring and health checks, a failover manager or clustering software, and data replication or state synchronization between the primary and standby. When a failure is detected, traffic or service requests are redirected to the standby through mechanisms such as virtual IPs, DNS failover, or load balancers, while fencing or isolating the failed component helps prevent data corruption and split-brain conditions.

Failover is often paired with failback, the process of returning operations to the original primary after repair, reconciliation, and resynchronization of data and state.

Benefits include reduced downtime and improved resilience; drawbacks can include complexity, cost, and potential data loss or inconsistency in asynchronous replication. Proper testing and regular drills are essential to validate failover readiness.

Typical use cases include databases, storage systems, network gateways, and cloud services. Good practice involves clear service-level objectives, automated testing, consistent replication, fencing, and well-defined procedures for initiating and auditing failover events.