ReverseProxy for IIS 6.0 in CS using ASP.NET

Problem to solve

We want to embed content from an internal webserver e.g. http://foo to our public webserver http://sar.informatik.hu-berlin.de. In particular the frontend request http://sar.informatik.hu-berlin.de/test/bla.html should get the response for http://foo/dir/bla.html. Thus the mapping is:

• http://sar.informatik.hu-berlin.de/test -> http://foo/dir.

From outside this should be look like a local web directory.

Used Software

IIS Reverse Proxy in particular v1.5. In that release of software redirections of the backend server are not forwarded transparently to the frontend. Therfore we patched the C-Sharpe code to take care of that. We disabled the internal handling MaximumRedirections = 0; of redirections and send them instead through the frontend to the browser. The differences are:

38c38
<   	const int MaximumRedirections = 50;
---
> 		const int MaximumRedirections = 0;
357a358,370
> 			switch((int) backEndResponse.StatusCode) {
> 				case 301:
> 				case 302:
> 				case 303:
> 				case 307:
> 					frontEndResponse.StatusCode = (int) backEndResponse.StatusCode;
> 					string newLocation = backEndResponse.Headers["Location"];
> 					newLocation = Regex.Replace(newLocation, backEndSite, 
> 						frontEndRequest.Url.GetLeftPart(UriPartial.Authority) + frontEndRequest.ApplicationPath, 
> 						RegexOptions.IgnoreCase);
> 					frontEndResponse.RedirectLocation = newLocation;
> 					break;
> 			}

Complete ReverseProxy.cs.

Then redirections which usally occur if you enter e.g. http://foo/dir -> http://foo/dir/ are forwarded to the browser as http://sar.informatik.hu-berlin.de/test -> http://sar.informatik.hu-berlin.de/test/

Installation

Based on W2k/XP, Win2003

Walk through

1. Create directory where software lives e.g. C:\Inetpub\test_virtual and extract archive "\\dc\pub\2006\2006 Software\ReverseProxy_15_SAR.zip" to that directory.
2. Create in the IIS MMC a virtual directory
3. Give the alias name under which the resource should be reachable by the frontend test
4. Select the Web Site Content Directory C:\Inetpub\test_virtual
5. OK.
6. Check the Properties of the virtual dir.
7. Press Create.
8. Press Configuration
9. Insert
10. Enter: Executable C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322\aspnet_isapi.dll and uncheck "Verify that file exists"
11. If you select .asax and then press Edit it should look like that:
12. Open cmd-prompt and to register ICSharpCode.SharpZipLib.dll and run

    cd C:\Inetpub\test_virtual

C:\Inetpub\test_virtual>C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322\gacutil.exe /i ICSharpCode.SharpZipLib.dll

1. Finally you have to configure the proxy by editing C:\Inetpub\test_virtual\Web.config

   <?xml version="1.0" encoding="utf-8" ?>

<configuration>

<appSettings> <add key="BackEndSite" value="http://foo/dir" /> </appSettings>

 <system.web>

...

Uninstalling

• Unregister the gzip-dll by running gacutil /u ICSharpCode.SharpZipLib.dll.
• Remove the virtual directory test in the IIS-MMC.
• Remove the directory C:\Inetpub\test_virtual.

--WM 12:54, 13 December 2006 (CET)