SAP Web Dispatcher 

Purpose

The SAP Web dispatcher lies between the Internet and your SAP system. It is the entry point for HTTP(s) requests into your system, which consists of one or more NetWeaver application servers. As a "software web switch", the SAP Web dispatcher can reject or accept connections. When it accepts a connection, it balances the load to ensure an even distribution across the servers.

You can use the SAP Web dispatcher in ABAP/Java systems and in pure Java systems, as well as in pure ABAP systems.

It is also beneficial to use the SAP Web dispatcher, if you do not need security functions (entry point in the DMZ, SSL, URL filtering), but you simply want to balance the load between several SAP NW AS instances.

Implementation Considerations

The SAP Web dispatcher is recommended when you use an SAP system with several SAP NW application servers for Web applications.

The SAP Web dispatcher is a program that you can run on the machine that is connected directly to the Internet. It requires minimal configuration - you just have to enter the following data in the profile file:

●     Port, on which the HTTP(s) requests are to be received (parameter icm/server_port_<xx>)

●     Host and HTTP port of the SAP message server (parameter rdisp/mshost and parameter ms/http_port)

If you should be able to call the Web application externally, for example using the URL www.shop.acme.com, this host name must be mapped internally to the SAP Web dispatcher. This then forwards the HTTP(S) request to a suitable application servers.

Features

The SAP Web dispatcher performs the following tasks:

Selects an appropriate application server (persistence with stateful applications, load balancing, ABAP or Java server), see Server Selection and Load Balancing Using the SAP Web Dispatcher.

Filters URLs – you can define URLs that are to be rejected, see SAP Web Dispatcher as a URL Filter

Web caching – you can use the SAP Web Dispatcher as a Web Cache to improve the response times and to conserver the application server cache.

Depending on the SSL configuration, forwards, terminates, and (re)encrypts requests. See SAP Web Dispatcher and SSL

Constraints

The SAP Web dispatcher is only useful in the Web environment. In the classic SAP system, load is balanced by the message server.

The SAP Web dispatcher forwards only incoming HTTP(S) requests to the Web application server and the response is then returned to the client.

Outgoing requests (such as requests to a different SAP Web Application Server) are not sent via the SAP Web dispatcher. They are sent via the proxy server for the appropriate intranet.

More Information

The documentation is split up into the following sections:

• Architecture of the SAP Web Dispatcher describes the structure and how the dispatcher works.
• Management of the SAP Web Dispatcher describes how to configure and manage the SAP Web dispatcher.
• Monitoring the SAP Web Dispatcher describes the monitoring functions and error analysis.
• The appendix contains a specification for the load balancing protocol. This is available in English only: Appendix: SAP Load Balancing Protocol Specification

You can find details of the change history of the SAP Web dispatcher in collective note SAP Web Dispatcher (SAP note 538405).