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.
i5/OS™ has provided an
application resilience architecture that supports various degrees of highly
available application. At the high end of this spectrum applications will
be enhanced with integrated functions that demonstrate highly available characteristics
and automation of the highly available environment, controlled by cluster
management utilities.
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 i5/OS 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.