SAP Web Dispatcher

Use

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 SAP 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. The SAP Web Dispatcher therefore contributes to security and also balances the load in your SAP system.

You can use the SAP Web dispatcher in in pure ABAP systems as well as in combined ABAP/Java systems (“dual-stack” systems), and in pure Java systems.

Recommendation

It is also useful to use the SAP Web Dispatcher if you only want to cover one aspect (security functions or load balancing). We also recommend that you 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 NetWeaver Application Server instances.

Implementation Considerations

The SAP Web dispatcher is recommended when you use an SAP system with several application server instances 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>)
Computer and HTTP port of SAP message servers (parameter rdisp/mshost and parameter ms/http_port or wdisp/system_ <xx>)

Example
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.

Downward Compatibility

Although the SAP Web Dispatcher is downward-compatible to older releases of SAP systems, there may be restrictions with release combinations of SAP Web Dispatcher and SAP system that are supported by SAP. The released release combinations are documented in Note 908097 Information published on SAP site .

In principle, SAP Web Dispatcher is released for older releases of SAP systems at the latest when the kernel release that the SAP Web Dispatcher is based on is released for use as the downward-compatible kernel for the SAP system.

Features

The SAP Web Dispatcher can perform the following tasks, among others:

Selection of appropriate application server – persistence with stateful applications, load balancing, ABAP or Java server.

More information: Server Selection and Load Balancing Using the SAP Web Dispatcher
Configuration for multiple systems - You can place a SAP Web Dispatcher in front of multiple SAP systems, and configure which requests go to which system, or perform load balancing across system boundaries.

More information: SAP Web Dispatcher for Multiple Systems
URL filtering - You can define URLs that you want to be rejected, and by doing so restrict access to your system.

More information: 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.

More information: SAP Web Dispatcher as a Web Cache
URL rewriting, manipulation of HTTP header fields – The Web Dispatcher can manipulate inbound HTTP requests in general on the basis of defined rules.

More information: Modifications of HTTP Requests
Depending on the SSL configuration you can forward, terminate, and (re)encrypt requests.

More information: SAP Web Dispatcher and SSL

Restrictions

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 incoming HTTP(S) requests to the application servers and returns the responses from the back end to the client.

Outgoing requests (such as requests to another SAP NetWeaver Application Server) are not sent using the SAP Web dispatcher. They are sent using 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, manage, and monitor the SAP Web Dispatcher.
In the appendix you can find the specification for retrieving and interpreting the list of available application servers. This is available in English only: SAP Application Server List Retrieval Specification.

You can find details of the change history of the SAP Web Dispatcher in collective note SAP Web Dispatcher (SAP note 538405 Information published on SAP site ).