In IBM® i high availability environments, application resiliency, which is the ability to restart an application on a backup system, is supported through the application cluster resource group (CRG). The takeover IP address allows access to the application without regard on which system the application is currently running. This capability allows resilient applications to be switched from one node to another in the event of an outage.
An application CRG can start an application as well as monitor for application failure. An application is defined to be a program or set of programs that can be called to deliver some business solution. The application CRG does not manage any data associated with the application. The data would be managed by a data or device CRG. The exit program in an application CRG serves two purposes. First, the exit program is invoked when cluster events occur to allow processing that is specific to that application for these events. The second purpose of the exit program is to start and then monitor the health of the actual application program. Although some business applications are created internally, others are purchased from outside vendors. If an application provider has made their application highly available, they would provide the CRG exit program along with the application. The exit program would be written to react appropriately to cluster events and manage the application.