I recently spent some time building an install package for a web application using WiX. There are some nice IIS extensions for WiX to help with that, but they're missing the ability to set some advanced properties, like an Application Pool's "Enable 32 Bit Applications" property.

Matt Honeycutt has a helpful posting on his blog about this. The basic idea is that you use a custom action to invoke Appcmd.exe and do whatever you need, and that can be done entirely with WiX markup -- no separate coding required.

I did need to alter Matt's approach a little, though, because it didn't work for me as it was. I would have just commented about this on his blog, but comments are closed.

When I ran my installer, I got a vague error saying that the custom action had failed. Running the MSI from the command line with the logging switch, and looking at the MSI log file didn't help. There was output saying that it was going to run the custom action, but no indication that it had failed, no result code from the Appcmd process, and nothing from stderr. It did show the complete command line for the action, however, so I copied it out into a command prompt and ran it. That failed saying I needed administrator privileges. Running in a command prompt started with "Run as Administrator" worked just fine.

It turns out that by default, custom actions impersonate the user that started the install, without the administrator elevation that the installer itself runs under. This can be changed by setting the CustomAction's Impersonate attribute to "no". That also required adding Execute="deferred", and as a result, having the custom action run before InstallFinalize rather than after.

Here's what it looks like:

<InstallExecuteSequence>
  <Custom Action="ConfigureAppPools" 
             Before="InstallFinalize"><![CDATA[NOT Installed AND VersionNT64 >= 600]]></Custom>
</InstallExecuteSequence>

<!-- Snip -->

<CustomAction Id="ConfigureAppPools" 
    Execute="deferred"
    Impersonate="no"
    Return="check"
    Directory="TARGETDIR"
    ExeCommand="[SystemFolder]inetsrv\appcmd set apppool /apppool.name:"[APPPOOLNAME]" /enable32BitAppOnWin64:true" />