Parallel Configuration of the SAP Internet Transaction Server

Use

This section describes how you can protect the SAP Internet Transaction Server (ITS) from failure by replicating its essential components on separate hosts. Parallel configuration not only improves system availability, it can also be used to improve performance during normal operation. To improve performance with parallel configuration of the ITS, we recommend using a multiplexer for intelligent load balancing.

Prerequisites

For more information on the basic configuration of the ITS, see Internet Transaction Server (AS-ABAP).

Features

The high availability setup for the ITS uses extra hosts to run parallel instances of the application gateway (AGate) and web gateway (WGate), as shown in the following graphic:

High Availability ITS Configuration

This configuration means that, if one ITS or one of its components (that is, an AGate or WGate) fails, there is always a remaining unit to take over. From SAP Release 4.6D, AGates and WGates can be linked together, as shown in the graphic.

Activities

The graphics below show what happens when the WGate or the AGate fails.

WGate Failure

This graphic shows what happens when WGate 1 on Host 1 fails:

When the WGate fails, HTTP requests are routed across the surviving WGate. Both AGates 1 and 2 continue to be used. Therefore, the session contexts are saved, and the mySAP Workplace users can continue working without interruption. However, this fault tolerance requires all AGates and WGates to be linked together, as shown in the previous graphic, “High Availability ITS Configuration”.

This scenario also applies to failure of the HTTP web server.

AGate Failure

This graphic shows what happens when AGate 1 on Host 2 fails:

When the AGate fails, the session contexts are lost, interrupting the mySAP Workplace user’s work. Therefore, a new session must be opened, for which HTTP requests are directed across WGate 2 in this example. The new session context is held on the surviving AGate 2.