Refer to the exhibit.

ClearPass Policy Manager allows you to designate one of the subscriber nodes in a cluster to be the Standby Publisher, thereby providing for that subscriber node to be automatically promoted to active Publisher status in the event that the Publisher goes out of service. This ensures that any service degradation is limited to an absolute minimum.

References: http://www.arubanetworks.com/techdocs/ClearPass/Aruba_DeployGd_HTML/Content/5%20Cluster%20Deployment/Standby_publisher.htm