Windows Server Failover Clustering (WSFC) is a feature of the Windows Server platform for improving the high availability (HA) of applications and services. WSFC, which is the successor to Microsoft Cluster Service (MSCS), can be administered through the Failover Cluster Manager snap-in.
With Windows Server Failover Clustering, each active server has another server identified as its standby server. In order for a failover cluster to work, each server's hardware specifications must be the same and the servers must share storage.
The two servers communicate through a series of "heartbeat" signals over a dedicated network. If the signals are initiated by the active server and sent to the standby signal at specific intervals, they are called push heartbeats. If the standby server does not receive a push heartbeat within a certain amount of time, it takes over and becomes the active server. Communication signals can also be sent from the standby server to the active server; these are called pull heartbeats. If the active server doesn't respond to a pull heartbeat within a certain amount of time, the standby server determines that the active server has failed and takes over.