Failover

A failover ( failover from the English for " failover ") is the unplanned change between two or more network services in a one-sided loss. As a result, the services can be kept highly available despite the failure of one of the systems.

Mission-critical applications such as databases, web server or e -mail can be found in this way even with a failure of one computer available because the second system takes over the tasks of the primary system in case of failure.

In most cases, both servers monitor each other with a heartbeat.

Since in a conscious transfer of the services we can speak of a cluster node to another not by an error ( failover ), referred to this process as a switchover.

Failover Clustering

A failover cluster or Active / Passive cluster is a group of two or more computers (cluster ), in which a second computer takes over the tasks of the failure of a computer.

The active system is the primary system, the waiting passive systems the backup or standby system.

In order for the failover automated and can be done without administrator intervention, the use of a cluster manager software is required.

Another advantage of a failover cluster is the ability to take a system for maintenance purposes deliberately out of service, the redundancy is no longer guaranteed during this period with a two - server cluster.