Introduction

Cassini is a web server written in C#, you'll find more information about it at http://www.asp.net/

These simple steps gets Apache up and running with ASP.NET

Download and install Apache 2.x for Windows (remember to stop IIS)

Modify the http.conf file:

# 
LoadModule proxy_module modules/mod_proxy.so
LoadModule proxy_connect_module modules/mod_proxy_connect.so
LoadModule proxy_http_module modules/mod_proxy_http.so
LoadModule rewrite_module modules/mod_rewrite.so 

# 
ProxyPass /aspnet http://127.0.0.1:8080/ 
ProxyPassReverse /aspnet http://127.0.0.1:8080/

Create a different catalog (not the /aspnet catalog in http.conf) for your ASP.NET files and start Cassini:
1. If you are using the cassini server included in WebMatrix
  c:\path-to-cassini\webserver.exe /port:8080 /path:"c:\path-to-asp.net-sourcefiles"
2. or, the stand-alone Cassini server
  c:\path-to-cassini\CassiniWebServer "c:\path-to-asp.net-sourcefiles" 8080

Test:

Cassini: http://localhost:8080/test.aspx
Apache: http://localhost/aspnet/test.aspx

<!-- test.aspx -->
<%@ Page Language="vb" %>
<html>
<body>
    <form runat="server">
        <asp:Calendar runat="server" />
    </form>
</body>
</html>

Ultimate test

If everything is working fine, you can move on to the 'ultimate' test, running ASP.NET Forums on Apache

Do a manual installation of ASP.NET Forums (skipping step 7)
See: http://www.asp.net/Forums/ShowPost.aspx?tabindex=1&PostID=21470

Add to http.conf (assumes the modifications above are done)

#AspNetForums
ProxyPass /AspNetForums http://127.0.0.1:8081/AspNetForums 
ProxyPassReverse /AspNetForums http://127.0.0.1:8081/AspNetForums 
#aspnet_client
ProxyPass /aspnet_client http://127.0.0.1:8082/aspnet_client 
ProxyPassReverse /aspnet_client http://127.0.0.1:8082/aspnet_client

Start 2 different Cassinis listening on port 8081 and 8082.
c:\path-to-cassini\webserver.exe /port:8081 /path:"c:\path-to-asp.net-forums" /vpath:"/AspNetForums" c:\path-to-cassini\webserver.exe /port:8082 /path:"E:\Program Files\ASP.NET\Client Files" /vpath:"/aspnet_client"

It is not the fastest solution, but everything works fine. I decided to "stress-test" it using Homer running 10 threads 5 sockets per thread in one minute, and got the following:

Page	Hits	TTFB^* Avg.	TTLB^* Avg.
/AspNetForums/Default.aspx	286	1024.96	7458.23

*: TTFB = Time To First Byte, TTLP = Time To Last Byte

Bear in mind that this test was done on my Thinkpad T21 800Mhz/512 MB, which is filled with junk.

Now I am waiting for someone to write a mod_cassini

Reference

http://www.dotnetguru.org/articles/DotNetFree/CassiniApache/ApacheASPNET.htm
http://www.clrgeeks.com/Papers/HostingASPNET/

Cassini and Apache 101