SAP Dispatcher: Structure, Functions, and Caveats

Architecture and Functions

Think of the SAP dispatcher as the gatekeeper of a gated community. He makes sure that authorized personnel enter and directs them to the appropriate place. The SAP 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. The SAP dispatcher can accept or reject connections. When it accepts a connection, it balances the load to ensure an even distribution across the servers. The SAP dispatcher plays a vital role in security and also balances the load in your SAP system to maximize efficiency. You can use the SAP dispatcher in ABAP/Java systems and in pure Java systems, as well as in pure ABAP systems.

Structure of the SAP Dispatcher

The architecture is the same as the architecture of the Internet Communication Manager (ICM). The SAP dispatcher uses the same HTTP paradigm and is likewise structured in modules from sub handlers. But unlike the ICM, the SAP dispatcher does not directly pass incoming requests to a work process (such as a server process). Instead, it sends them to the ICM of the application server. The response of the application server to a request returns to the client using the same network connection via the dispatcher. If the application server, acting as the client, opens connections to external HTTP servers, these connections go direct to the server (or possibly via a configured proxy) and not via the SAP dispatcher. The SAP dispatcher has the function of a “reverse proxy,” rather than that of a “proxy.”

Directing HTTP Requests

Like the ICM, the SAP dispatcher uses a number of handlers to process incoming requests. With the exception of the ABAP handler and the Java handler, the handlers are called in the exact same sequence as conventional processing of HTTP requests. The dispatching handler comes last and enacts the load balancing, then forwards the request to the ICM of the appropriate application server.

Functions

The SAP Web dispatcher performs the following tasks:

· Selects appropriate application server (persistence with stateful applications, load balancing, ABAP or Java server).

· Filters URLs. You can define URLs that you want to be rejected, and by doing so restrict access to your system.

· Acts as Web cache. You can use the SAP dispatcher as a Web Cache to improve the response times and to conserve the application server cache.

· Manipulates requests. Depending on the SSL configuration, you can forward, terminate, and (re)encrypt requests.

Caveats

The SAP dispatcher is only useful in the Web environment. In the classic SAP system, load is balanced by the message server. Also, the SAP dispatcher forwards incoming HTTP requests to the application servers and returns the responses from the back end to the client. Outgoing requests (such as requests to a different SAP Web Application Server) are not sent via the SAP dispatcher. They are sent via the proxy server for the appropriate intranet.

Recommendations

It’s a good idea to use the SAP dispatcher when you use an SAP system with several SAP NW AS instances for Web applications. The SAP dispatcher is a program that you can run on the machine that is connected directly to the Internet. And, it is easy to get it set up. It requires minimal configuration; you just have to enter some simple parameters into the profile. The SAP dispatcher is helpful whether you want to cover one or both aspects of its functionality. If your main interest is in security functions, SAP dispatcher is your answer. If it is in load balancing, SAP dispatcher is your answer too. You get both benefits in one application.

Like any good gatekeeper, the SAP dispatcher gets to know the neighborhood and maintains everyone’s safety while keeping things running smoothly. At 1st Basis, we can make sure your SAP dispatcher conforms to your actual needs. Get the gatekeeper. Contact us today.

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