IIS returns 500 when Node app returns a 4xx

I have also asked this on the iisnode github project

I am using IISNode via a Windows Azure Website.

If my Node app returns a 2xx status code (200, 201, etc), then all is well and works as expected.

if my Node app returns a 4xx status code, for example: response.send(404, "not found") (I am using Restify) then I get a 500 sent to the client and the body is simply "The page cannot be displayed because an internal server error has occurred."

If I do azure site log tail <sitename>, then when the 500 gets sent to the client, the log contains HTML of a 404.

...
<body> 
<div id="content"> 
<div class="content-container"> 
<h3>HTTP Error 404.0 - Not Found</h3> 
<h4>The resource you are looking for has been removed, had its name changed,
or is temporarily unavailable.</h4> 
</div> 
...

I really just want IISNode/IIS to take my 404 and send it on down to the client. This is also true of 401s, 409s, etc. They all cause a 500 to get sent instead.

I have tried <customErrors mode="off" /> and <httpErrors existingResponse="passThrough" /> in my web.config to no avail. Here is my web.config now:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <system.web>
    <customErrors mode="off" />
  </system.web>
  <system.webServer>         
    <httpErrors existingResponse="PassThrough" />
    <staticContent>
       <mimeMap fileExtension=".svg" mimeType="image/svg+xml" />
       <mimeMap fileExtension=".ico" mimeType="image/x-icon" />
    </staticContent>
    <handlers>
      <add name="iisnode" path="server.js" verb="*" modules="iisnode"/>
    </handlers>
    <rewrite>
      <rules>
        <rule name="DynamicContent">
           <conditions>
            <add input="{REQUEST_FILENAME}" matchType="IsFile" negate="True"/>
           </conditions>
           <action type="Rewrite" url="server.js"/>
           <match url="/*" />
        </rule>
      </rules>
    </rewrite>
  </system.webServer>
</configuration>

For what it's worth, I can't get IISnode to do anything but return 200s from my node app. Trying to get IIS to serve my static files, enable node-inspector, or really any of the more interesting IISNode features cause a 500 for me. No idea why, and would love to get past it!

Similar StackOverflow Questions

this question is pretty much exactly my problem. Except that <httpErrors existingResponse="PassThrough" /> does not work for me. I feel like I have something more fundamentally wrong with my IISNode setup, so if anyone has any ideas on things to try I'm all ears.

Solution

for some reason the following section in your config is causing this issue:

<staticContent>
    <mimeMap fileExtension=".svg" mimeType="image/svg+xml" />
    <mimeMap fileExtension=".ico" mimeType="image/x-icon" />
</staticContent>

As a workaround, remove this section if possible and retry. I will investigate why this section is causing this issue.