Can't stop firing ASP.NET Module for static content

Question

I have a module in an ASP.NET MVC application. The module is working fine, but it's firing for every type of file including static content even though I have:

<modules  runAllManagedModulesForAllRequests="false">
    <add name="MyModule" ... / >
</modules>

The module hooks AcquireRequestState and PostRequestHandlerExecute events and both show static content firing (.htm, .css, .png etc.).

I was under the impression that runAllManagedModulesForAllRequests="false" should keep modules from firing on non-ASP.NET content.

To clarify:

I can set preCondition="managedHandler" like this:

<add name="MyModule" type="MyApp.MyModule" preCondition="managedHandler" />

and get my module to fire only managed requests.

However, I'm trying to understand why the IIS pipeline in general is firing managed module hits for every request. I think this used to work just fine in older versions where unless runAllManagedModulesForAllRequests="true" it wasn't firing unmanaged content into ASP.NET modules.

Running on IIS8 on Windows 8 64 bit mode, with integrated pipeline mode.

Update:

After some more research it turns out that the following is true:

• if runAllManagedModulesForAllRequests="true" all modules - regardless of their preCondition attribute setting fire on all requests. This also true for Application_XXXX events implement on the HttpApplication
• runAllManagedModulesForAllRequests="false" has no effect of keeping unmanaged requests from hitting modules, unless preCondition="managedHandler" is set
• runAllManagedModulesForAllRequests="false" does affect Application_XXXX events, causing those events to only fire on managed requests then. IOW, Application_XXXX behaves as if the 'module' implementation had a preCondition="managedHandler"

For more detailed information on this I posted a blog entry: http://www.west-wind.com/weblog/posts/2012/Oct/25/Caveats-with-the-runAllManagedModulesForAllRequests-in-IIS-78

Answer 1

In IIS7 Microsoft introduced a new way of developing modules and handlers by using managed (.NET) code, not just native code. Problem is switching a request between managed and native code is very expensive, so Microsoft introduced the preCondition="managedHandler". It flags the module as only available for managed content requests (.aspx, .asmx, ...) so IIS avoids firing it for static content.

Now, you can have a situation where you want to modify an static content request, such as minifying JavaScript on the fly. You can write the module using C# and compile it as a managed module, but you want it to be fired for static content, so you simply do not mark it as managedHandler.

Finally, runAllManagedModulesForAllRequests="true" is used to override preCondition="managedHandler" so all of them get fired.

There is more info available at:
http://www.iis.net/learn/get-started/introduction-to-iis/iis-modules-overview#Precondition