Definition

Failover is the automatic or manual switching of operations from a failed primary system to a secondary (standby) system.

Core concept

In high-availability setups, a standby server is kept updated and ready. If the primary fails (hardware/network crash), failover redirects traffic to the standby with minimal downtime.

Use cases

Database clusters (e.g. two-node replication), application servers with hot standby. Ensures continuity of service.

Trade-offs

There is typically a slight delay during failover. If not automatic, it requires detection logic and possibly manual intervention. Proper design is needed to avoid split-brain (see above).

Example

Oracle Data Guard or AWS RDS Multi-AZ use automatic failover: the standby takes over transparently to clients when primary is unreachable[[36]](https://www.ibm.com/docs/en/db2/11.5.x?topic=strategies-failover "High availability through failover").

References

“Failover is the transfer of workload from a primary to a secondary system in the event of a primary failure”[[36]](https://www.ibm.com/docs/en/db2/11.5.x?topic=strategies-failover "High availability through failover").