Workflow Service (WF4) in IIS7.5 Application Pool/Worker Process Mixing Issue

Question

Problem

WCF requests for my 2 Workflow Services in different Application Pools are not being processed by their respective worker processes. Instead, both worker processes are processing WCF requests for both Workflow Services. This problem only occurs in "Integrated" Managed Pipeline Mode but not "Classic" Managed Pipeline Mode.

Setup

• 2 Worflow Services (Workflow Foundation 4.0) running in IIS 7.5.
• Each Workflow Service is setup as an application in IIS and has it's own Application Pool, with its own Identity credentials.
• The Application Pools are running in "Integrated" Managed Pipeline Mode.

Description

Let's just say for example, I have Workflow Service A (WFSA) and B (WFSB) running under UserA and UserB respectively. They both are expecting WCF calls via Receive activities in the workflow.

When I start the 2 Application Pools, I can see 2 w3wp.exe worker processes running, one as UserA and the other as UserB. I expect that w3wp.exe worker process for UserA should handle WCF requests for WFSA, and w3wp.exe worker process for UserB should handle WCF requests for WFSB.

However, when I start sending WCF messages to the workflows, I can see through the trace log files that both w3wp.exe processes are handling requests for both Workflow Services.

For example, WCF messages for WFSA are being handle by the w3wp.exe worker processes for UserA AND UserB. So if I send 10 WCF messages to WFSA, 4 would be handled by w3wp.exe for UserA, and 6 would be handled by w3wp.exe for UserB.

When I switch the Application Pool to "Classic" Managed Pipeline Mode, the WCF messages are routed to the respective worker processes, as expected.

Is there some configuration that I'm missing?

Any help is greatly appreciated.

Update

In the project I'm working on, WFSA, WFSB, and another WCF Service Application (WCFApp) communicate with each other in the following configuration:

WFSA <==> WFSB <==> WCFApp

We see problems in the following scenario:

• WFSA ==> WFSB (UserA): WFSA instantiates a new workflow on WFSB, which is processed on w3wp.exe for UserA.
• WFSB (UserA) ==> WCFApp: WFSB calls the WCFApp, which does some processing.
• WCFApp ==> WFSB (UserB!!!): After processing, WCFApp notifies WFSB that it's done. But the WCF message gets handled by the w3wp.exe process for UserB!!! Of course the workflow instance does not exist there, so it errors out with the following message:

The requested resource has moved to the one of the following locations: http://server/AppFolder/WFSB.xamlx/INotifyWhenDone

I can work around this by setting:

<workflowIdle timeToUnload="00:00:00" />

This means the workflow will get persisted immediately when it goes idle, and messages going to the wrong worker process can be processed because it can find the workflow instance in the persistence database. However, this solution is unacceptable because persistence is VERY SLOW.

Answer 1

There are a couple of hot fixes for AppFabric, one of which seems to be related to the problems you are experiencing. Seek here for the links.

Answer 2

I'm getting the feeling that both services are registering something like the same 'identifier' with IIS, though what this is I couldn't tell you (Correlation Id perhaps?). Hence messages are routed to both services. I also get the feeling that in the integrated pipeline there is only one optimised pipe to the services and multiple services register with it (which is what leads to my earlier point).