Sub Domain Implementation using Urlrewriter.NET (ASP.NET + IIS6)

Subject

You CAN implement URL rewriting for a virtual sub domain in your ASP.NET application using: Urlrewriter.NET + ASP.NET 2.0/3.5 under IIS6.

At first look, it's not obvious how this is done. However, using some code tips and snippets from around the web, I have accomplished this.

Background

My team had to upload an ASP.NET 3.5 application which actually held 2 applications. The first had to be available through www.strauss-group.com, and the second had to be available through OfficeCoffee.strauss-group.com.

After investigating some methods, including ISAPI filters, we decided to implement this feature using an HttpModule. We chose Urlrewriter.NET.

Everything was going quite smooth - until the point that we had to actually configure the rewriting in the web.config file. There seems to be lack of documentation around the internet. That said, I am writing this tip in light of the missing documentation.

Summary of Steps for Implementation

Step 1

Download the main package from Urlrewriter.NET.

Step 2

Follow the instructions in the readme.txt file (from the downloaded package). They tell you exactly what to add to the web.config file:

1. Add the <configSection ...> directive
2. Add the <httpModule ...> directive
3. Add the <rewriter ...> directive

Step 3

Make sure the DNS servers point to your server (alternatively: see "testing" section below).

Step 4

Configure your <rewriter ...> section. Here is the relevant part of the web.config:

<?xml version="1.0"?>
<configuration>
<rewriter>
    <if header="HTTP_HOST" match="^(officecoffee\.)([^.]+)\.([^.]+)$">
      <!--
		<rewrite url="~/afh/css/(.*)" to="~/afh/css/$1" processing="stop" ></rewrite>
		<rewrite url="~/afh/js/(.*)" to="~/afh/js/$1" processing="stop" ></rewrite>
		-->
      <rewrite url="~/Documents/(.*)" to="~/Documents/$1" processing="stop"></rewrite>
      <rewrite url="~/PageFiles/(.*)" to="~/PageFiles/$1" processing="stop"></rewrite>

      <rewrite url="~/he/(.*)" to="~/he/$1" processing="stop" ></rewrite>

      <rewrite url="~/afh(.*)" to="~/afh$1" processing="stop" ></rewrite>

      <rewrite url="~/ScriptResource.axd(.*)" to="~/ScriptResource.axd$1" processing="stop" >
      </rewrite>
      <rewrite url="~/WebResource.axd(.*)" to="~/WebResource.axd$1" processing="stop" >
      </rewrite>

      <rewrite url="/" to="/he/afh-folder/afhhomepage/" processing="stop" ></rewrite>

    </if>

  </rewriter>

Quick Explanation

The key to implementing the sub domain URL rewriting is the directive:

<if header="HTTP_HOST" match="^(officecoffee\.)([^.]+)\.([^.]+)$">

In fact - without that directive, you can't rewrite the URL on a sub-domain basis.

The "match" attribute is a RegEx which finds our sub domain pattern in the relevant part of the URL.

Another issue to notice is the processing="stop" attribute, which was very important for us. The instruction "stop" means that if a match was found and a URL rewriting was performed - than there is no need to further process the rewriting according to other <rewrite> sections. This was very useful for us since we were running the application under a CMS (specifically: EPiServer CMS). And CMS systems have their own "folders" and target URLs that come under consideration when applying URL rewriting.

Testing

You can configure your "hosts" file (c:\windows\system32\drivers\etc) and add the following lines:

127.0.0.1    www.strauss-group.com

127.0.0.1    OfficeCoffee.strauss-group.com 

This can simulate the DNS on your development machine.

Hope this helps my friends!