The cluster resource group exit program is called during different phases of a cluster environment.
This program establishes the environment necessary resiliency for resources within a cluster. The exit program is optional for a resilient device CRG but is required for the other CRG types. When a cluster resource group exit program is used, it is called on the occurrence of cluster-wide events, including when:
This exit program:
When a cluster resource group API is run, the exit program is called from a separate job with the user profile specified on the Create Cluster Resource Group (QcstCreateClusterResourceGroup) API. The separate job is automatically created by the API when the exit program is called. If the exit program for a data CRG is unsuccessful or ends abnormally, the cluster resource group exit program is called on all active nodes in the recovery domain with an action code of Undo. This action code allows any unfinished activity to be backed out and the original state of the cluster resource group to be recovered.
If the exit program for an application CRG is unsuccessful or ends abnormally, cluster resource services will attempt to restart the application if the status of the CRG is active. The cluster resource group exit program is called with an action code of Restart. If the application cannot be restarted in the specified maximum number of attempts, the cluster resource group exit program is called with an action code of Failover. The restart count is reset only when the exit program is called with an action code of start, which can be the result of a start CRG, a failover, or a switchover.
When the cluster resource group is started, the application CRG exit program called on the primary node is not to return control to cluster resource services until the application itself ends or an error occurs. After an application CRG is active, if cluster resource services must notify the application CRG exit program of some event, another instance of the exit program is started in a different job. Any other action code other than Start or Restart is expected to return.
When a cluster resource group exit program is called, it is passed a set of parameters that identify the cluster event being processed, the current state of the cluster resources, and the expected state of the cluster resources.
For complete information about cluster resource group exit programs, including what information is passed to the exit program for each action code, see Cluster Resource Group Exit Program in the Cluster API documentation. Sample source code has been provided in the QUSRTOOL library which can be used as a basis for writing an exit program. See the TCSTAPPEXT member in the QATTSYSC file.