A Java cluster installation consists of:
? One or more Instances of the AS Java
? The Central Services, which also form an instance
? One or several databases
The different instances can be split up among different physical machines. The Central Services (Message Service and Enqueue Service) are installed on one host that meets possible requirements for high availability.
The following figure shows the simplest installation of the usage type AS Java. A system installed in this way can process only requests to Java applications. The integrated scenario with Java and ABAP is described in the section SAP NetWeaver Application Server with ABAP and Java.
The minimal AS Java installation consists of:
? A Java central instance with a dispatcher, a server process, and the Software Deployment Manager (SDM).
? The Central Services instance.
? The Database.
A Java Instance consists of (with the exception of Central Services):
? a Java Dispatcher
? One or several server processes
The figure below shows a larger Java cluster installation. It consists of four instances, all of which have an instance number and each one can be started, stopped, and monitored separately.
If you have a large Java cluster installation, the load is distributed between the available dialog instances by a load balancer. This scenario with implementation of the SAP Web Dispatcher is described in the section Load Balancing of Java Applications.
You will find further information on the cluster architecture in the following sections: