Sun Cluster 3.1 10/03 Data Services Developer's Guide

Analyzing the Application for Suitability

The first step in creating a data service is to determine that the target application satisfies the requirements for being made highly available or scalable. If the application fails to meet all requirements, you might be able to modify the application source code to make it so.

The list that follows summarizes the requirements for an application to be made highly available or scalable. If you need more detail or if you need to modify the application source code, refer to Appendix B, Sample Data Service Code Listings.

Note –

A scalable service must meet all the following conditions for high availability as well as some additional criteria.

Additionally, scalable services must meet the following requirements.

For a scalable service, application characteristics also determine the load-balancing policy. For example, the load-balancing policy, LB_WEIGHTED, which allows any instance to respond to client requests, does not work for an application that makes use of an in-memory cache on the server for client connections. In this case, you should specify a load-balancing policy that restricts a given client's traffic to one instance of the application. The load-balancing policies, LB_STICKY and LB_STICKY_WILD, repeatedly send all requests by a client to the same application instance—where they can make use of an in-memory cache. Note that if multiple client requests come in from different clients, the RGM distributes the requests among the instances of the service. See Implementing a Failover Resource for more information about setting the load balancing policy for scalable data services.