Is it possible to get the current machine name in IIS 7.5 Url Rewrite Module Rules? - iis

Question

The HTTP_HOST and SERVER_NAME server variables give me the host name from the HTTP request (which can be an IP address or the load-balanced DNS based on how the request was made). I could not find a server variable that will give me actual machine name (i.e., the value of the COMPUTERNAME environment variable).
I am trying to set-up some redirection rules on a server-farm and there are some rules based on what the current machine name is (e.g., internal machines have int in their name). I don't want to create separate rules for each machine, and instead want to have some conditional logic based on the current machine name. I cannot seem to find a way to get hold of the machine name.
Any ideas?

Answer 1

In IIS7 The computer name isn't one of the built-in server variables. However all is not lost, with a bit of work using a custom UrlRewrite provider you can surface your machine name in a rewrite rule.
Scott Forsyth has actually built something like this already and has written a blog post describing its use, and provided the source and a pre-built binary + installer:
URLRewrite ServerNameVariable Provider
For the sake of preserving this information in the event of that article disappearing here are loosely the steps:
Start by creating a new class library project in Visual Studio. You can find the steps to do this here:
Developing a Custom Rewrite Provider for URL Rewrite Module (IIS.NET)
They are in essence (in case the link dies):
Create a Class Library project and call it something like ServerNameProvider. You need to make sure the project is a .NET 2.0 or 3.5 project. IIS7.5 managed code support still targets the 2.0 runtime.
Rename the default Class1.cs file to a name that reflects the provider purpose, for example: ServerName.cs - and just make sure the class name in the source reflects this as well.
Add a reference to: %ProgramFiles%\Reference Assemblies\Microsoft\IIS\Microsoft.Web.Iis.Rewrite.dll.
In the project properties create a strong name key (on the signing tab)
Add a post-build event to install the provider assembly in your dev PC GAC (just for testing):
CALL "%VS90COMNTOOLS%\vsvars32.bat" > NULL
gacutil.exe /if "$(TargetPath)"
Note, if using Visual Studio 2010 then the environment variable %VS90COMNTOOLS% should be changed to %VS100COMNTOOLS%.
Open up the ServerName.cs file and make sure your class implements the Microsoft.Web.Iis.Rewrite.IRewriteProvider interface:
using System.Collections.Generic;
using Microsoft.Web.Iis.Rewrite;
namespace ServerNameVariable
{
public class ServerName : IRewriteProvider
{
public void Initialize(IDictionary<string, string> settings,
IRewriteContext rewriteContext)
{
}
public string Rewrite(string value)
{
return System.Environment.MachineName;
}
}
}
Build the project. On your local PC the assembly will be installed into the GAC.
Register the provider with IIS:
appcmd.exe set config -section:system.webServer/rewrite/providers /+"[name='ServerNameVariable',type='ServerNameVariable.ServerName, ServerNameVariable, Version=1.0.0.0, Culture=neutral, PublicKeyToken=5854ff76fb5c07af']" /commit:apphost
Make sure the PublicKeyToken value in the command line above matches your assembly's public key token. You can extract that value by doing sn.exe -T <assemblyfile.dll>, for example:
e:\AppDev\..bin\Debug> sn.exe -T ServerNameVariable.dll
Microsoft (R) .NET Framework Strong Name Utility Version 4.0.30319.1
Copyright (c) Microsoft Corporation. All rights reserved.
Public key token is 5854ff76fb5c07af
The next thing to do is use your new provider in a rewrite rule, for example, here's the example Scott gave which is an outbound rule:
<outboundRules>
<rule name="Set Custom Header" enabled="true">
<match serverVariable="RESPONSE_X_Machine_Name" pattern=".*" />
<action type="Rewrite" value="{ServerNameVariable:}" />
</rule>
</outboundRules>
And here's a simple inbound rule that redirects to google.com if the machine name is BOB:
<rewrite>
<rules>
<rule name="TestServerVariableProvider"
enabled="true"
stopProcessing="true">
<match url=".*" />
<conditions>
<add input="{ServerNameVariable:}" pattern="BOB" />
</conditions>
<action type="Redirect"
url="http://google.com"
appendQueryString="false"
redirectType="Found" />
</rule>
</rules>
</rewrite>