Applications on clusters can be divided into three basic types:
A single-instance application runs on only one cluster member at a time. In order to make this type of application highly available, the cluster must provide a mechanism for starting the application on another cluster member in the event that the current member can no longer run the application. The TruCluster Server high availability mechanism for single-instance applications is the cluster application availability (CAA) subsystem; see Chapter 5 for a description of CAA.
The TruCluster Server Highly Available Applications manual provides detailed information about moving applications from the TruCluster Software Version 1.* series of products to TruCluster Server Version 5.0A.
A multi-instance application can run on multiple cluster members at the same time. A multi-instance application by definition is highly available because the failure of one cluster member does not affect the instances of the application running on other members. See Chapter 6 for a discussion of how cluster aliases provide transparent client access to multi-instance applications.
A distributed application is specifically designed to run on a cluster, using different members for specific purposes. These applications use the Memory Channel, distributed lock manager (DLM), and cluster alias application programming interfaces (APIs) to integrate applications with cluster resources.
TruCluster Server lets you run components of distributed applications in parallel, providing high availability while taking advantage of cluster-specific synchronization mechanisms and performance optimizations.
See Chapter 6, Chapter 7, Chapter 8, and the TruCluster Server Highly Available Applications manual for more information on the subsystems and interfaces used to create distributed applications.