failover
/ˈfeɪlˌoʊvər/noun
Failover is the switch from a primary system to a backup system when the primary system fails or stops working correctly.
After the failure, failover automatically redirected traffic to the backup server.
During failover, a secondary server, Glossary · In briefdatabaseA database is a structured collection of data that software can store, retrieve and modify. A database management system controls access to that data.Read more, network connection or external service takes over from a failed component. This helps an application remain available or recover faster, limiting Glossary · In briefdowntimeDowntime is the period when software, a system or an online service is unavailable or its essential functions cannot be used.Read more. A usable backup system must be ready and have access to current data.
How does failover happen?
Glossary · In briefmonitoringMonitoring systematically tracks software, infrastructure or processes through measurements and checks. Deviations can trigger alerts so an administrator can investigate.Read more or a technical check detects that the primary component has stopped responding or is returning errors. The system then redirects traffic or processing to the backup. A database replica might take over the primary role, or a load balancer might send web traffic to another server.
The switch can be fully automatic or require administrator approval. Its speed depends on the infrastructure, data synchronization and time needed to start a backup component, among other things. After recovery, traffic is often switched back to the original system in a controlled way.
A backup alone is not enough
A second server or provider does not by itself provide working failover. The system must reliably detect failures, know when to switch and prevent two components from processing changes at the same time. It must also be clear how much recent data may be lost during a failure.
Teams therefore test the full procedure regularly. They check whether connections are re-established, background tasks continue and users see the correct data. Testing also reveals whether the backup has enough capacity to take over the load. Failover reduces the impact of a failure, but its cause still needs to be investigated and fixed.