Apache::ForwardedFor

The Apache::ForwardedFor module is an excellent Perl tool that allows you to reset remote_ip to the incoming client's IP when running mod_perl behind a reverse proxy server. It sets the first IP from X-Forwarded-For header, which your reverse proxy server creates, to the remote_ip connection property.

Using Apache::ForwardedFor is breezy. You only need to add a few lines to your httpd.conf file to configure it. The PerlModule Apache::ForwardedFor and PerlPostReadRequestHandler Apache::ForwardedFor lines set the module, while the PerlSetVar ForwardedForAccept 192.168.1.1 and PerlAddVar ForwardedForAccept 192.168.1.2 lines allow you to define the IP addresses to accept incoming connections from.

One of the most common use cases of Apache::ForwardedFor is to run Apache behind a reverse proxy so that you can delegate static content requests to a small httpd and proxy dynamic mod_perl-generated content requests to a big httpd. This method helps overcome memory constraints of running a busy mod_perl site.

However, when using a reverse proxy, the backend (mod_perl) httpd's remote_ip is that of the front-end proxying httpd. This is not an accurate representation of the end client's real IP address, which can make it difficult to implement IP-based access control and track usage through your logs. Apache::ForwardedFor conveniently fixes this problem, allowing you to use IP-based access control and accurately track usage.