Excel Services and Web Gardens

I haven't seen too much on this, and it caused me some pain, so I thought I'd share...  We use very large Web Servers (24GB) with Web Gardens to utilize all that memory. 

The problem comes in with Shared Services.  Most Shared Services operate perfectly fine in a Web Garden.  Excel Services, specifically with Charting, is an exception.  For some reason, perhaps performance related, ECS will generate Charts using two separate requests to the Shared Services, one for the workbook, on for the Chart Image. 

The problem is that when sending in the second request, more likely than not you will get a difference process thread in the Web Garden than your original request.  This creates a disconnect, as they are not separate autonomous requests, but are linked.

The result is a wonderful ECS error on your page that says "Failed to Download Excel Services Chart".  This is backed up by MOSS log files that indicate that a "SOAP exception occurred" during "ExceuteWebMethod" in GetImage.  The actual error will show as a session timeout (because of inactivity).

The fix is simple.  Shared Services cannot have multiple threads.  You can set this in the properties of the Application Pool.  Just go to your IIS manager (on each WFE server) and right-click the Application Pool for Shared Services.  On the Performance Tab, change the Threads value back to "1".  No more Web Garden for Shared Services.  You can Web Garden your Content Web Apps without and surprises, just not your Shared Services.

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