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SAP WebDispatcher
The SAP WebDispatcher is needed in multiserver environments to serve as a central gateway
for incoming HTTP traffic. In the role as a central gateway, the SAP WebDispatcher can reject
or accept HTTP or HTTPS connections and can temporarily buffer incoming requests. If the
requests are accepted, the dispatcher distributes them to the ABAP and Java instances. The
SAP WebDispatcher is also responsible for load balancing in the SAP system
Distribution through ICM: Apart from the SAP WebDispatcher, web requests can also be
distributed through the ICM, which is used in traditional SAP systems. However, the ICM
server has only limited functions. Therefore, do not use it for web access.
For security reasons, the SAP WebDispatcher is installed on a separate host in a
demilitarized zone (DMZ). A DMZ is a neutral zone between the SAP system with its private
network and a public network. In this case, it isolates the SAP NetWeaver AS and the public
Internet. With this type of setup, external users cannot access SAP NetWeaver directly.
The SAP WebDispatcher is also a stand-alone component that enables a redundant setup to
provide a high availability environment.
2.1.3 SAP NetWeaver Application Server and runtime environment
The SAP NetWeaver AS is a main component of the application platform for SAP NetWeaver.
It provides reliable run times for both SAP proprietary programming languages of ABAP (AS
ABAP) and Java (AS Java). Based on open standards, such as HTTPS, SMTP, SSL, HTML,
XML, and Unicode, SAP NetWeaver AS creates the basis for web-based applications and the
complete service-oriented approach. SAP recommends running multiple instances of
application servers on different hosts. If one server fails, another server can take over the
workload.
ABAP is the main programming language for developing SAP software. ABAP is a
fourth-generation language and is for SAP business programming. ABAP programs and any
processed data, both business data and the corresponding metadata (such as GUI
definitions), are stored in the database.
The runtime environment for AS ABAP was originally built as the foundation of the
client/server system SAP R/3. This 3-tier client/server architecture provides scalability across
multiple application servers and decouples them from the underlying database management
system (DBMS).
The 3-tier client/server architecture, shown in Figure 2-3 on page 14, consists of the following
components:
► Presentation layer. The client is represented by a user interface program that is activated
by a user or another application. It connects to the application server system by using
network connections. As shown in Figure 2-3 on page 14, different technologies are
available to access a system: the traditional SAP GUI, a browser interface, and in
accordance with the SAP strategy, an interface for mobile devices.
► Application layer. The application server level runs the business logic that is in the
programs to handle requests from the client. An SAP system can contain a cluster of
application server instances (1….n) that can be distributed across various hosts (AIX,
Linux on System x, Linux on System z, and Microsoft Windows). Because business data is
not locally persisted on the application layer, a DBMS is needed.
Chapter 2. Architectural overview of SAP NetWeaver with DB2 for z/OS 13