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Application Interface Levels

LifeKeeper provides a foundation for event detection and recovery control as well as an overall environment and tool set for ensuring application availability. This topic along with Interface Issues for Common Application Types and Interface Definition Tasks describe:

Interface Levels

Your involvement in ensuring high availability for your application begins with the proper choice and configuration of the application. For instance, if you need high availability for applications involving database transactions, you must select or develop an application that provides features such as logging, archiving, roll forward/rollback facilities and controllable internal recovery techniques.

Next, you should decide how to implement the three levels of application interfaces supported by LifeKeeper:

Dependency Definition

In order to ensure availability, you must determine the application’s dependency upon other system resources and determine how to discover and handle errors in those resources. LifeKeeper lets you define dependency relationships (hierarchies) using either the LifeKeeper GUI or the command line interface.

Error Detection and Handling

Providing detection and alarming for problems within an application is critical to building the best total fault resilient solution. Since every application varies on the mechanism and format of failures, no one set of generic mechanisms can be supplied. In general, however, many application configurations can rely on the core system error detection provided within LifeKeeper. The Recovery Scenarios topic describes three common fault situations to demonstrate the power of LifeKeeper's core facilities.

LifeKeeper also provides a complete environment for defining errors, alarms and events that can trigger recovery procedures. This interfacing usually requires pattern match definitions for the system error log (/var/log/messages) or custom-built application-specific monitor processes.

Recovery Actions

Fault resilience depends upon the definition of recovery actions for the various anticipated fault conditions. LifeKeeper uses shell scripts to specify recovery actions for protected resources. For LifeKeeper, the two required recovery scripts for any application resource are restore and remove, used whenever LifeKeeper needs to place an application in service or out-of-service, respectively.

The Recovery Scripts topic lists the various types of scripts that LifeKeeper recognizes and provides descriptions and examples that can help you create customized scripts.

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