One Webdispatcher for multiple systems

Introduction

With the introduction of the SAP Webdispatcher 7.2 a significant improvement has been introduced, hence the ability to connect to multiple SAP and non-SAP systems with only one Webdispatcher.
When having this implemented, only one Webdispatcher has to be administrated and only one, or a limited number of ports, in the DMZ has be opened to access all systems.
Although this new feature is documented very well, it is still unknown at a significant group of people. Therefore I would like to bring this feature to the attention by writing a blog.

Classic setup

In the classic setup of the SAP Webdispatcher, each system needed to have its own Webdispatcher. Only in case of a dual stack (ABAP + Java) one Webdispatcher could be used for dispatching requests between an ABAP and a Java system.
Since NetWeaver 7.0 EHP1 SAP recommends installing systems using the single stack option. Only SAP PI and Mobile Infrastructure, dual stacks are still the recommended way.
Especially this “new” strategy of stack deployment requires more flexibility from components like a Webdispatcher.
For example: You want to provide access to an SRM Portal via the internet. In this case the Portal accesses ABAP webdynpro in the Portal. So both the Portal as the SRM ABAP back-end need to be accessed via the Webdispatcher in the DMZ.

Different scenario’s

Implementing the SAP Webdispatcher to server multiple systems is quite easy. In this example I will only focus on one way to achieve this, which is in my opinion the most easy and most convenient way to implement this functionality.
This scenario is called “Control Using Modification Rules”. For this scenario you need to have an alias of the Webdispatcher host name for each system. 
For all scenario’s please check the following documentation:
http://help.sap.com/saphelp_nwce72/helpdata/en/03/afe24bfeb7419b9172ffb6e7636926/frameset.htm

How to implement the new functionality

Install the Webdispatcher 7.2. For the installation of the Webdispatcher 7.2, download the Installation master and kernel DVD. Execute the installation following the installtion guide. You can also just download the Webdispatcher package from the support packages and patches area and install it via the bootstrap function. 

Landscape setup

In this example, I used the following components:
PIP – SAP PI 7.0 ABAP+Java
Message server http port: 8100
Hostname sappi.demo.com

CE2 – SAP CE7.2 Java only
Message server http port 8141
Hostname sapce.demo.com

WD2 – SAP Webdispatcher 7.2
Hostname webdisp.demo.com
ICM http port: 4444

After having the webdispatcher installed, you have to make the following modifications in the instance profile of the webdispatcher:

wdisp/system_0 = SID=PIP, MSHOST=sappi.demo.com, MSPORT=8100
wdisp/system_1 = SID=CE2, MSHOST=sapce.demo.com, MSPORT=8141
icm/HTTP/mod_0 = PREFIX=/,FILE=/sapmnt/WD2/profile/icm_filter.txt

Create the file icm_filter.txt with the following contents:
if %{HTTP_HOST} regimatch wd_sappi.demo.com*
SetHeader x-sap-webdisp-target-sid PIP [break]

if %{HTTP_HOST} regimatch wd_sapce.demo.com*
SetHeader x-sap-webdisp-target-sid CE2 [break]

Restart and test the result

After the changes to the instance profile have been made and the Webdispatcher has been restarted, we can test the result.
Logon to internet explorer using the alias host name of the system you would like to select:
http://wd_sappi.demo.com:4444 -> request goes to PIP
http://wd_sapce.demo.com:4444 -> request goes to CE2

In the Webdispatcher administration console a separate node has been added in the menu for each system. 

Result

By implementing this functionality, the number of Webdispatchers can be reduced significantly. Also the number of ports that have to be opened can be reduced to one or a couple..