I've written a couple times about what configuration changes cause AppDomain recycles.  Most recently how the ASP.NET tab causes a server-wide AppDomain recycle, and previously about changes in ASP.NET 2.0.

Here I'm going to cover things that, when done in IIS 7, will cause a full application pool recycle.  I obtained the following list from the Microsoft.com folk at Microsoft.  They worked with the IIS team during IIS 7 development to get a complete list of all settings which cause full app pool recycles.  What this means is that if you make changes to applicationHost.config that touches anything in the following list, the applicable application pool will be recycled.  If you change other settings to applicationHost.config, the app pools on the server will remain unaffected.

Note: It's important to realize that an application pool in IIS is different than an AppDomain in ASP.NET.  The previous blog posts were about AppDomain recycles, but this one is about application pool recycles. 

Windows Activation Process Service (WAS) recycles an application pool if you change the configuration of any of the following:

• Restart parameters (for example, restart time, number of requests, and scheduled memory)
• Idle timeout
• Ping interval
• Startup and shutdown time limit
• Orphan action
• CLR version
• Pipeline mode
• A 32 to 64 bit worker process
• Job objects (for example, CPU limit)
• CPU affinity
• Worker process identity

Essentially this means that virtually any change to the application pool settings will cause it to immediately recycle, so be careful when making a change to an app pool.  This applies when using IIS Manager, any of the programming APIs or if you edit applicationHost.config directly.  You may need to schedule to setting change off hours if you don't want a recycle to occur at an inopportune time.  Changes to global settings will not cause the application pools on the server to recycle.

I was just asked to help someone troubleshoot a site that worked fine on Windows Server 2003 / IIS6 but didn't work on Windows Server 2008 / IIS7.  A file was in a folder under the bin folder on the site and displayed an error when trying to view the page.  The path looked something like this:

http://www.sitename.com/subfolder/bin/debug/file.xml

The subfolder wasn't marked as an application, although that doesn't really matter.  The point is that since /bin/ was in the path somewhere, IIS7 wouldn't allow the file.xml to be displayed.  It served up a 404.2 error saying file or directory not found.

404 - File or directory not found.

The resource you are looking for might have been removed, had its name changed, or is temporarily unavailable.

Since I knew that it worked in IIS6, I knew that it wasn't asp.net that was blocking it, so I looked in applicationHost.config and found the following under the <requestFiltering> section:

                <hiddenSegments applyToWebDAV="true">
                    <add segment="web.config" />
                    <add segment="bin" />
                    <add segment="App_code" />
                    <add segment="App_GlobalResources" />
                    <add segment="App_LocalResources" />
                    <add segment="App_WebReferences" />
                    <add segment="App_Data" />
                    <add segment="App_Browsers" />
                </hiddenSegments>

So, IIS7 now blocks those key folders and doesn't allow them to be seen.  To the outside world, any page in any of these folders appears to not exist.

There may be times when you really do want to display the page, as in this particular case.  Not to worry, it can be changed easily enough.  This setting in on purpose though, so you usually shouldn't remove it for the whole site.

You can use AppCmd or do it manually from applicationHost.config or web.config.  Since requestFiltering is allowed to be set at the site or folder level by default, it's probably best to set a web.config file in the folder that you want to allow.

To do this, create a web.config file in your folder and type or paste the following into it.  I should look something like this:

<?xml version="1.0"?>
<configuration>
   <system.webServer>
       <security>
          <requestFiltering>
               <hiddenSegments>
                   <remove segment="bin" />
               </hiddenSegments>
           </requestFiltering>
       </security>
   </system.webServer>
</configuration>

If you want to make the change to your applicationHost.config file instead, you can do it by adding a location tag to the bottom of the file (well, almost the bottom - along with the other location tags) like this:

    <location path="sitename.com/subfolder/bin/debug">
        <system.webServer>
            <security>
               <requestFiltering>
                    <hiddenSegments>
                        <remove segment="bin" />
                    </hiddenSegments>
                </requestFiltering>
            </security>
        </system.webServer>
    </location>

You can do this using AppCmd instead.  Just drop to the command prompt and type the following: (Be sure to change the paths to the correct page before running this.)

C:\Windows\System32\inetsrv\appcmd.exe set config "sitename.com/subfolder/bin/debug" -section:system.webServer/security/requestFiltering /-hiddenSegments.[segment='bin']

After making this change, you will be able to view pages normally, even if they have /bin in the site path.