March 2011

Say you want to enable reverse proxy on a site powered by Apache Web Server where all traffic to the web site it reverse proxied to a different server, but you want to exclude certain paths from being reverse proxies. I don’t know why you would want to do that :).. but we ran into that scenario at work and I wanted to document the config for future reference. The picture below shows a high level view of the traffic

• Ensure the following modules are being loaded in Apache.

[bash]

LoadModule proxy_module modules/mod_proxy.so
LoadModule proxy_balancer_module modules/mod_proxy_balancer.so
LoadModule proxy_connect_module modules/mod_proxy_connect.so
LoadModule proxy_ftp_module modules/mod_proxy_ftp.so
LoadModule proxy_http_module modules/mod_proxy_http.so
LoadModule rewrite_module modules/mod_rewrite.so

[/bash]

• In the virtual host configuration for kudithipudi.org add the following lines

[bash]

ProxyRequests Off

<Proxy *>
Order deny,allow
Allow from all
</Proxy>

ProxyPass /static !
ProxyPass /media !
ProxyPass / http://INTERNAL_SERVER:8888
ProxyPassReverse / http://INTERNAL_SERVER:8888

[/bash]

This is a quick trick I came up with to find out the IP address of a client that is trying to access a farm of web servers that you have access to. The diagram below shows the network path for a typical web server.

You have a client that might be sitting behind a (or multiple) proxy server. And there is a load balancer involved because you have multiple web servers for redundancy.

We were recently working on some rewrite rules for our web servers at work and we needed to find out what IP address the web servers were seeing the client traffic come from. Couple of challenges

• Which web server do you check? The load balancer can send you traffic to any server.
• What IP address are you going to look for? Wait that is the original problem right :).

The web servers usually write an entry to the error log when they serve a 404 error. So we can use that to figure out which web server you are hitting and what IP address the web server is seeing you as. Here’s the trick

• On the client side go to http://WEBSITE_ADDRESS/Get_Me_My_IP (or some other URL, which you know doesn’t exist on the web site)
• On the server side, grep for “Get_Me_My_IP” in the web server error logs

Here is an example, I ran on this website (https://kudithipudi.org)

• Client Side : Go to https://kudithipudi.org/what_is_my_ip
• Server Side : grep for “what_is_my_ip”

[bash]
root@samurai:/var/log/apache2# grep -i what_is_my_ip access_kudithipudi.log
199.27.130.105 – – [04/Mar/2011:16:07:18 +0000] "GET /what_is_my_ip HTTP/1.0" 40 4 5495 "-" "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.14) Gecko/2 0110218 Firefox/3.6.14 ( .NET CLR 3.5.30729; .NET4.0E)"
[/bash]

• From this entry I can figure out that my client is appearing as “199.27.130.105” to the web server.