Load Balancing Between Many Java Instances 

The following graphic shows a system with several Java dispatchers, to which the SAP Web Dispatcher is the entry point in the DMZ. This executes the load balancing between the Java dispatchers, which then distribute the requests to their server processes.

Instead of the SAP Web dispatcher you can use any other load balancing device. You have to register it on the server and ports. The communication with the message server and the mapping to the SAP logon group are then no longer required.

 

The SAP Web dispatcher fetches the information it needs from the message server: This information includes the hosts and ports of the Java dispatcher, and the capacities of the connected J2EE engines, so that the SAP Web dispatcher can apply the weighted round robin procedure.

For this the SAP Web dispatcher simply needs, in its profile file, the port where it can reach the message server (parameter ms/http_port or ms/https_port). See also Example: Profile File of a SAP Web Dispatcher.

SAP Web Dispatcher

The SAP Web dispatcher is delivered with Central Services (enqueue service and message service). In the standard installation you will find this in the directory /usr/sap/<SID>/SCS01/exe.

If there are any patches you will find them on the SAP Service Marketplace under SAP NETWEAVER  ®  SAP NETWEAVER 04  ®  Binary Patches ®SAP J2EE ENGINE 6.30 ® OS Dependent Parts of Java Runtime of the required SP. In this packet you can find the SCS packet that contains icmadmin.sar as well as the SAP Web dispatcher.

Integration

The SAP Web dispatcher can be used for load balancing in the following scenarios:

·        Java-only scenario, as described here. As all requests are forwarded to J2EE Engines, all the distribution procedures using the URL prefixes in the SAP Web Dispatcher documentation are not relevant.

·        ABAP-only scenario, see SAP Web Dispatcher

·        Integrated scenario (Java+ABAP), see SAP Web Application Server with ABAP and Java, section Installation with Several Different SAP Web AS Instances

For more information about load balancing in the Java environment see the following sections:

Load Balancing by the Java Dispatcher

Load Balancing for J2EE Applications