Sun Java System Application Server Enterprise Edition 8.1 2005Q2 Administration Guide

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## What is the Application Server?

The Application Server provides a robust J2EE platform for the development, deployment, and management of enterprise applications. Key features include transaction management, performance, scalability, security, and integration. The Application Server supports services from Web publishing to enterprise-scale transaction processing, while enabling developers to build applications based on JavaServer Pages (JSPTM), Java servlets, and Enterprise JavaBeansTM (EJBTM) technology.

The Application Server Enterprise Edition provides advanced clustering and failover technologies. These features enable you to run scalable and highly available J2EE applications.

- Clustering - A cluster is a group of application server instances that work together as one logical entity. Each Application Server instance in the cluster has the same configuration and the same applications deployed to it.

  Horizontal scaling is achieved by adding Application Server instances to a cluster, thereby increasing the capacity of the system. It is possible to add Application Server instances to a cluster without disrupting service. The HTTP, RMI/IIOP, and JMS load balancing systems distribute requests to healthy Application Server instances in the cluster.

- High Availability - Availability allows for failover protection of Application Server instances in a cluster. If one application server instance goes down, another Application Server instance takes over the sessions that were assigned to the unavailable server. Session information is stored in the high-availability database (HADB). HADB supports the persistence of HTTP sessions and stateful session beans.

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