The following figure shows a system with several Java dispatchers, to which the SAP Web Dispatcher is the entry point in the DMZ. It 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. Using the device’s configuration tools, you have to register the communication ports of the Java dispatchers of the AS Java instances running behind it. The communication with the Message Server and the mapping to the SAP logon group are then no longer required.
Instance-level Load Balancing using SAP Web Dispatcher
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 load balancing algorithm.
To configure communication with the Message Server, you have to enter the HTTP or HTTPS port of the Message Server (parameter ms/http_port or ms/https_port) to the profile file of the SAP Web dispatcher. See also Example: Profile File of a SAP Web Dispatcher.
The SAP Web dispatcher is delivered with the Central Services instance (Enqueue Service and Message Service). In the standard installation, you can find it in the directory \usr\sap\<SID>\SCS<nr>\exe.
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 Engine, 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 and ABAP). For more information, see SAP NetWeaver Application Server with ABAP and Java
For more information about load balancing in the Java environment, see the following sections: