I ran into a nasty little problem today when deploying an application using ASP.NET 4.0 Routing to my live server. The application and its Routing were working just fine on my dev machine (Windows 7 and IIS 7.5), but when I deployed (Windows 2008 R1 and IIS 7.0) Routing would just not work. Every time I hit a routed url IIS would just throw up a 404 error:


This is an IIS error, not an ASP.NET error so this doesn’t actually come from ASP.NET’s routing engine but from IIS’s handling of expressionless URLs. Note that it’s clearly falling through all the way to the StaticFile handler which is the last handler to fire in the typical IIS handler list. In other words IIS is trying to parse the extension less URL and not firing it into ASP.NET but failing.

As I mentioned on my local machine this all worked fine and to make sure local and live setups match I re-copied my Web.config, double checked handler mappings in IIS and re-copied the actual application assemblies to the server. It all looked exactly matched. However no workey on the server with IIS 7.0!!!

Finally, totally by chance, I remembered the runAllManagedModulesForAllRequests attribute flag on the modules key in web.config and set it to true:

    <modules runAllManagedModulesForAllRequests="true">
      <add name="ScriptCompressionModule" type="Westwind.Web.ScriptCompressionModule,Westwind.Web" />

And lo and behold, Routing started working on the live server and IIS 7.0!

This seems really obvious now of course, but the really tricky thing about this is that on IIS 7.5 this key is not necessary. So on my Windows 7 machine ASP.NET Routing was working just fine without the key set. However on IIS 7.0 on my live server the same missing setting was not working. On IIS 7.0 this key must be present or Routing will not work.

Oddly on IIS 7.5 it appears that you can’t even turn off the behavior – setting runtAllManagedModuleForAllRequests="false" had no effect at all and Routing continued to work just fine even with the flag set to false, which is NOT what I would have expected.

Kind of disappointing too that Windows Server 2008 (R1) can’t be upgraded to IIS 7.5. It sure seems like that should have been possible since the OS server core changes in R2 are pretty minor. For the future I really hope Microsoft will allow updating IIS versions without tying them explicitly to the OS. It looks like that with the release of IIS Express Microsoft has taken some steps to untie some of those tight OS links from IIS. Let’s hope that’s the case for the future – it sure is nice to run the same IIS version on dev and live boxes, but upgrading live servers is too big a deal to do just because an updated OS release came out.

Moral of the story – never assume that your dev setup will work as is on the live setup. It took me forever to figure this out because I assumed that because my web.config on the local machine was fine and working and I copied all relevant web.config data to the server it can’t be the configuration settings. I was looking everywhere but in the .config file forever before getting desperate and remembering the flag when I accidentally checked the intellisense settings in the modules key.

Never assume anything. The other moral is: Try to keep your dev machine and server OS’s in sync whenever possible. Maybe it’s time to upgrade to Windows Server 2008 R2 after all.

More info on Extensionless URLs in IIS

Want to find out more exactly on how extensionless Urls work on IIS 7? The check out  How ASP.NET MVC Routing Works and its Impact on the Performance of Static Requests which goes into great detail on the complexities of the process. Thanks to Jeff Graves for pointing me at this article – a great linked reference for this topic!