Failover is the process of recovering the system to overcome a crash. For this process to occur, it is necessary to implement mechanisms at various levels of a solution, such as physical structure, communication links, cooling, hardware, database, application, etc. The purpose of this process is for the system to continue working even with failures in some components.
Failback is the process of restoring a system after failover. The goal is to return the system to its pre-failure state.