Connection to the Application 

HTTP Connection

If theTREX system is connected to a Java application, the Java application communicates with both the name server and with the Web server. The Java application asks the name server via TCP/IP for the address of a Web server. It then sends the request to the Web server using HTTP/HTTPS. The Web server forwards the request TREX-internally. The graphic below depicts this communication:

There are multiple Web servers in a distributed TREX system. As soon as the Java application receives the address of one Web server, it communicates with that Web server for as long as it is available. If the Web server does not answer (for example, because it is overloaded), the Java application swaps to another Web server.

RFC Connection

If the TREX system is connected to an ABAP application (that is, to an SAP system), both systems communicate via an RFC connection. The SAP system sends its requests to an SAP gateway. The SAP gateway sends the requests to a TREX RFC server. The TREX RFC server forwards the requests TREX-internally.

With regard to the SAP gateway, there are two variants:

·        Communication takes place using the local SAP gateway of the application server.

·        Communication takes place using a central SAP gateway.

In the case of a distributed TREX system, SAP strongly recommends using the local SAP gateways of the application servers. On the TREX side, TREX RFC servers are registered with each local SAP gateway. Each TREX host is connected to each application server of the SAP system.

The graphic below depicts this.

Using the local SAP gateways has the following benefits:

·        The local SAP gateways process the requests quicker then a central SAP gateway.

·        The SAP gateway is not a “single point of failure.” If an application server and its local SAP gateway fails, the requests are distributed among the remaining application servers and still continue to reach the TREX system.

If you use a central SAP gateway and the SAP gateway fails, the RFC connection fails too. It is not possible to switch to another central SAP gateway automatically.