High availability (HA) means planning a system design that delivers operational continuity and stands through any unplanned contingencies or planned downtime over a period of time. Microsoft offers HA solutions with failover clustering and Network Load Balancing (NLB) for several of its applications and services (roles). Both of these HA strategies serve different purposes.

Failover clustering involves configuring a group of servers, called nodes, to act as one server and serve one or more roles. One of these nodes acts as the active node, and rest nodes supplement as secondary or passive nodes for a particular role. When the primary, or active, node fails, any one of the passive nodes takes over the role, limiting the downtime and thereby increasing availability. The process in which the role is passed from the active node to a passive node is referred to as failover.

The NLB cluster is a collection of servers, referred...