Active/passive clustering is a solution that uses clustering software and special purpose hardware to minimize system downtime. Active/passive clusters are groups of computing resources that are implemented to provide high availability of software and hardware computing services. Active/passive clusters operate by having redundant groups of resources (such as CPU, disk storage, network connections, and software applications) that provide service when the primary system resources fail.

In a high availability active/passive clustered environment, one of the nodes in the cluster will be active and the other nodes will be inactive. When the active node fails, the cluster fails over to one of the inactive nodes automatically. As a part of this failover process, clustering software will start the resources on the redundant node in a predefined order (or resource dependency) to ensure that the entire node comes back up correctly.

Universal Messaging can run in an active/passive cluster environment, under Windows or UNIX. This approach does not provide load balancing or scalability.