# What is Failover?

> Failover is the capability and process of transferring a service from an active component, system, connection, or site to a redundant or standby alternative after a failure or abnormal condition.

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- Language: en
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## Content

It may be automatic or operator-initiated. The intended result is restored or continued service, but acceptable interruption, capacity, state, and correctness must be defined in advance.

Reliable failover depends on trustworthy health signals, decision rules, standby readiness, state replication, dependency coverage, routing or name changes, and prevention of conflicting active instances. Failback to the recovered primary is a separate controlled change and can carry its own risk.

### Key points

- **Set trigger logic:** Define failure evidence, detection and confirmation timing, quorum or fencing rules, authority for manual action, and safeguards against oscillation or false failover.
- **Cover dependencies:** Include data, identity, keys, networks, control planes, suppliers, capacity, configuration, observability, and the paths users need to reach the alternate service.
- **Test transitions:** Exercise failover and failback under load and partial-failure scenarios, verify transactions and data consistency, measure recovery objectives, and record degraded features.
- **Important limitation:** A successful component switch does not prove end-to-end continuity. Shared dependencies, stale or corrupted state, split-brain operation, incompatible configuration, insufficient capacity, or an attacker present in both environments can make failover ineffective or unsafe.

### Related terms

[Fault tolerance](<https://yellowcube.eu/glossary/fault-tolerance/>) · [Disaster recovery](<https://yellowcube.eu/glossary/disaster-recovery/>) · [Business continuity](<https://yellowcube.eu/glossary/business-continuity/>) · [Recovery time objective (RTO)](<https://yellowcube.eu/glossary/recovery-time-objective/>) · [Cyber resilience](<https://yellowcube.eu/glossary/cyber-resilience/>)

### Sources

[NIST, Failover](https://csrc.nist.gov/glossary/term/failover) · [NIST SP 800-53 Rev. 5, Security and Privacy Controls for Information Systems and Organizations](https://csrc.nist.gov/pubs/sp/800/53/r5/upd1/final) · [NIST SP 800-34 Rev. 1, Contingency Planning Guide for Federal Information Systems](https://csrc.nist.gov/pubs/sp/800/34/r1/upd1/final)

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