IIS AAR - URL Rewrite for reverse proxy - how to send HTTP_HOST

Question

Trying to use AAR as a reverse proxy in front of several back end IIS servers.

• One public ip address assigned to the server running IIS/AAR

• Then outbound URL rewrite rules are setup to redirect to one of several back end servers depending on hostname.

Works somewhat, but always returns the back end servers default site (not the one mapped to a hostname) so it looks like the host name (HTTP_HOST) is not getting passed from the proxy server to the back end server.

(I've verified bypassing the reverse proxy by editing hosts and the back end server returns the correct site bound to the host header)

This is an example of the rule (192.168.0.99 is the internal server, site.myco.com is the hostname)

    <rewrite>
        <rules>
            <rule name="ReverseProxyInboundRule1" stopProcessing="true">
                <match url="(.*)" />
                <action type="Rewrite" url="http://192.168.1.99/{R:1}" />                   
            </rule>
        </rules>
    </rewrite>

Have tried putting sever variables so

    <!-- Guessing server.myco.com is hard coded -->
    <serverVariables>
        <set name="HTTP_HOST" value="server.myco.com" />
    </serverVariables>

    <!-- Guessing picked up dynamically from incoming request host header -->
    <serverVariables>
        <set name="HTTP_HOST" value="{HTTP_HOST}" />
    </serverVariables>

But alas always returns the default binding - any ideas?

Answer 1

This post has the answer - Modifying headers with IIS7 Application Request Routing

Need to enable preserveHostHeader - can't see how you do that in the UI but this works

Run this from command line to update Machine/webroot/apphost config

%windir%\system32\inetsrv\appcmd.exe set config -section:system.webServer/proxy -preserveHostHeader:true /commit:apphost

Answer 2

My guess would be that your server doesn't allow you to change the server variable HTTP_HOST when you rewrite the URL.

At the level of the website where the URL rewrite is applied:

Then click the Add... link on the right tab and add your HTTP_HOST variable: