1. A method for managing a plurality of applications in a computer cluster, each application being able to run on a particular node in the computer cluster, wherein the computer cluster comprises a plurality of nodes hosted by a plurality of physical computers, the method comprising: maintaining associations among a plurality of modes and the plurality of applications, wherein each application is associated with at least one mode, and wherein the plurality of modes includes at least one recovery mode, each recovery mode being associated with a set of nodes that are related to one another; responsive to designation of at least one mode in the plurality of modes as active for the computer cluster so that there is at least one active mode for the computer cluster: explicitly flagging as eligible for activation each application that is associated with an active mode, including applications that are already active and associated with the active mode and applications that are inactive and associated with the active mode; flagging as ineligible for activation each application that is inactive and is not associated with any active mode; and flagging as ineligible for activation and inactivating each application that is active and is not associated with any active mode; wherein the steps of flagging as eligible, flagging as ineligible, and flagging as ineligible and inactivating are performed in any order, and wherein the inactivating is sequenced according to dependencies among the applications; responsive to explicitly flagging as eligible for activation each application that is associated with an active mode, activating each application flagged as eligible for activation that is inactive; and responsive to a threshold number of nodes in the set of nodes becoming unavailable, designating as active for the computer cluster an appropriate recovery mode associated with the set of nodes that includes the threshold number of unavailable nodes so that at least one application that is equivalent to at least one corresponding application that had been available on at least one node in the threshold number of unavailable nodes becomes available on another node in the computer cluster, wherein the another node in the computer cluster is external to the set of nodes that includes the threshold number of unavailable nodes.