IBM i architecture for cluster-enabled applications

Additional end-user value is provided by any application that is highly available, recognizing applications that continue to be available in the event of an outage, planned or unplanned.

IBM® i has provided an application resilience architecture that supports various degrees of highly available application. Applications on the high end of this spectrum demonstrate highly available characteristics, provide automation of the highly available environment, and are managed through high availability management interfaces.

These applications have the following characteristics:

• The application can switch over to a backup cluster node when the primary node becomes unavailable.
• The application defines the resilient environment in the Resilient Definition and Status Data Area to enable automatic configuration and activation of the application by a cluster management application.
• The application provides application resilience by means of an application CRG exit program to handle cluster related events, taking advantage of the capabilities of the IBM i cluster resource services.
• The application provides an application restart function that repositions the user to an application menu screen or beyond.

Applications that demonstrate more stringent availability and restart characteristics have the following characteristics:

• The application provides enhanced application resilience through more robust handling of cluster events (action codes) by the application CRG exit program.
• The application provides a greater level of application restart support. For host-centric applications, the user will be repositioned to a transaction boundary by commitment control or checkpoint functions. For client-centric applications, the user will experience a seamless failover with minimal service interruption.