Why does a reverse proxy rewrite rule stop working when System.Web.Routing is active?

Question

Boiling this down to the simplest possible rule:

      <rule name="Reverse Proxy" stopProcessing="true">
          <match url="^external/(.*)" />
          <action type="Rewrite" url="http://some-site/{R:1}" />
      </rule>

("Enable Proxy" is checked in the ARR Server Proxy settings at the server level).

The above rewrite rule works fine in a very simple test app with a web.config containing the section, it works fine in a web forms app, but if I put the same rule into an MVC3 app (on the same machine, so identical config for IIS higher up) it never has any effect; the request flows through.

if it's just a rewrite (and not a reverse proxy) it works OK, e.g.,

          <rule name="rewrite to internal" stopProcessing="true">
              <match url="^internal/(.*)" />
              <action type="Rewrite" url="different-internal/{R:1}" />
          </rule>

...is fine.

I can get the reverse proxy rule to work if I add

        routes.IgnoreRoute("external/{*pathInfo}");

in the Global.asax.cs class, so that my request for external/* doesn't hit the default controller, but I don't understand why. I think the URL rewrite module kicks in way before the Routing (see http://learn.iis.net/page.aspx/496/iis-url-rewriting-and-aspnet-routing/) so I'd expect there not to be a conflict between them.

Is the Routing module adding in "virtual" rewrite rules to the URL rewrite module, that are overriding my declared rewrite rules?

Angelo Angelo · Accepted Answer · 2012-08-06T12:06:36

I had this exact same issue and it took me the entire day to find the solution.

Find: the ServoceModel tag in your Web.config file and add the serviceHostingEnvironment code as seen below:

      <system.serviceModel>
        <serviceHostingEnvironment aspNetCompatibilityEnabled="true" multipleSiteBindingsEnabled="true" />
      </system.serviceModel>

This will allow routes to be passed through to IIS to handle it.

One more tip, I recommend anyone having routing issues with their MVC projects to install Remote Debugger via NuGet. This will tell you what routes are being activated when.

Why does a reverse proxy rewrite rule stop working when System.Web.Routing is active?

1 Answers