URL Rewrite keeps original host Location when reverse proxy 301 redirects

Question

I have URL Rewrite setup on an IIS 7.5 site: http://site1.com/

This acts as a reverse proxy to the second site: http://site2.com/

Here is the flow of events:

Answer 1

As I said in the above comments, I believe the default behavior of the reverse proxy is to pass through the response untouched (assumes there are no outbound rewrite rules set). I haven't tested your scenario specifically with a 301 response from the server behind the proxy, though.

If a special outbound rule is in fact needed, this code will modify the HTTP location header of all 301 responses to http://site3.com/somepath

<outboundRules>
  <!-- This rule changes the domain in the HTTP location header for redirect responses -->
  <rule name="Change Location Header">
    <match serverVariable="RESPONSE_LOCATION" pattern="^http://[^/]+/(.*)" />
    <conditions>
      <add input="{RESPONSE_STATUS}" pattern="^301" />
    </conditions>
    <action type="Rewrite" value="http://www.site3.com/{R:1}" />
  </rule>
</outboundRules>

This rule is a slight modification of one posted in URL Rewrite Module 2.0 Configuration Reference

Answer 2

Could Application Request Routing be involved? Look at IIS -> Machine or Site -> Application Request Routing Cache -> Server Proxy Settings and uncheck the "Reverse rewrite host in response headers" checkbox. If you do this at the machine level, it'll take effect for all sites. If you do it on a particular site, it'll only take effect for that site, and other sites on the box will be unaffected.