International Data Corp. In order for failover to occur, each node in the cluster must be in constant contact with the others, usually by way of an electronic pulse or heartbeat. When a node stops emitting the heartbeat, the other nodes realize it has failed, and failover kicks in. The work is then divvied up among the other clusters or taken on by just one, depending on pre-determined instructions. Clusters can be configured to failover in a variety of ways. For example, a node can failover to another in a different location in the event of a disaster.
Some configurations have an extra node in the cluster that is usually idle.
In cases of failover, the idle node takes over and the cluster capacity isn't compromised. Such functionality also comes into play during routine maintenance. For example, one node can be taken offline and its work shifted to another server for upgrades or maintenance. Virtually every server operating system can support clustering to some extent. Generally, the choice of Unix or Windows, Linux or mainframe operating systems will be guided by the applications architecture, said Richardson.