Wednesday, April 11, 2007

java Architecture tutorial

2 Availability Availability is about assuring that services are available to the required number of users for the required proportion of time. Availability requires that the topology provide some degree of process redundancy in order to eliminate single points of failure. While vertical scalability can provide this by creating multiple processes, the physical machine then becomes a single point of failure. For this reason a high-availability topology typically involves horizontal scaling across multiple machines. Hardware-based high availability: By providing both vertical and horizontal scalability the WebSphere Application Server runtime architecture eliminates a given application server process as a single point of failure. In fact the only single point of failure in the WebSphere runtime is the database server where the WebSphere administrative repository resides. It is on the database server that any hardware-based high availability (HA) solutions such as HACMP, Sun Cluster, or MC/ServiceGuard should be configured. Extensibility Ability to modify or add functionality without impacting the existing functionality. The key to an extensible

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