ActiveStandby

Activestandby, often written as active-standby, refers to a redundancy arrangement in which one component or system is designated as the active unit performing the workload while one or more standby units remain idle or in a ready state to assume control if the active unit fails or is taken offline. This approach is commonly used to improve system availability and continuity of service in IT infrastructure, networking, and power systems.

In operation, the active unit routinely communicates its health and status to the standby unit(s) through heartbeat signals or monitoring. If a failure is detected or maintenance is required, the standby takes over with minimal disruption. Depending on the implementation, state or data may be replicated to the standby to reduce data loss; this can be synchronous (near real-time) or asynchronous.

Common variations include hot standby, where the standby is fully ready and can take over immediately; and cold standby, where the standby is not running and requires startup time. Warm standby falls between these extremes. Activestandby contrasts with active-active configurations, where multiple units actively share the workload simultaneously.

Applications include network devices with redundant failover, server clusters, storage arrays in mirror configurations, and power supplies in hardware systems with redundant rails. Advantages include reduced downtime, simpler failover logic, and predictable recovery times. Drawbacks include higher hardware costs, the risk of a single failure in the failover mechanism, and potential data inconsistency if replication is not perfectly synchronized.

See also: high availability, redundancy, failover, active-active, heartbeat.