The SAP Web Dispatcher acts as a Single Point Of Access to the SAP System for users acessing the system via Browser (IE, FF). Therefore, it is located between the Internet / Intranet and the SAP System. The Web Dispachter acts as a load balancer and can redirect, 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(SAP WD) is only useful in web-enabled scenarios. This is, when the SAP systems are accessed over HTTP(S). In a normal R/3 / ECC scenario the users will access the systems over the SAPGui and won't utilize the Web Dispatcher. The SAP WD can be used in ABAP/Java systems and in pure Java systems, as well as in pure ABAP systems. The usage is recommended when you use an SAP system with several SAP Web Application Servers for Web applications. The Web Dispatcher is associated with one Application Server (AS). This has to be the AS where the Message Server (MS) is running. One Web Dispatcher can only be associated with one AS.
The Web Dispatcher connects itself with the message server of the associated AS. The Web Dispatcher uses the information from the MS to selects an appropriate application server (persistence with stateful applications, load balancing, ABAP or Java server). The SAP WD also understands and supports logon groups (both for ABAP and Java).
The SAP WD supports High Availability (HA) at process level. This means, that on the machine where the SAP WD is running a monitoring process checks whether the SAP WD is running or not. If the SAP WD stops working, the monitoring process restart the SAP WD. This means, that for a certain time (the time between the stop and the restart of the SAP WD) no access to the SAP System is possible over the SAP WD and all session data is lost.
To enable a HA of the SAP WD, you can use one of the following solutions:
- DNS: Round Rubin load balancing
- 3rd party hardware / software load balancing
Signle Point Of Access
The SAP WD acts as an Single Point Of Access (SPOA) and therefore, also as a Single Point Of Failure (SPOF). You can leverage the SPOA functionality to simplify your landscape.