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, 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; 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; and 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.