Issue

1. Setup a simple 2-node reverse proxy setup -- i.e., one frontend system using ProxyPass & ProxyPassReverse to forward to another backend system, e.g.:

   [root@frontend ~]# echo ProxyPass / http://backend.example.com/ >/etc/httpd/conf.d/proxy-to-backend.conf
   [root@frontend ~]# echo ProxyPassReverse / http://backend.example.com/ >>/etc/httpd/conf.d/proxy-to-backend.conf
   

2. Make sure the backend system has mod_remoteip loaded

   [root@backend ~]# grep -r mod_remoteip /etc/httpd/
   /etc/httpd/conf.modules.d/00-base.conf:LoadModule remoteip_module modules/mod_remoteip.so
   

3. Declare RemoteIPHeader on the backend and ensure access logging includes the %a token, e.g.:

   [root@backend ~]# echo RemoteIPHeader X-Forwarded-For >/etc/httpd/conf.d/remoteip.conf
   [root@backend ~]# echo 'LogFormat "%a %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-Agent}i\"" modremoteip >>/etc/httpd/conf.d/remoteip.conf
   [root@backend ~]# echo 'CustomLog "logs/test-modremoteip" modremoteip' >>/etc/httpd/conf.d/remoteip.conf
   

4. Test getting content from the frontend and notice the IP that shows up in the backend log is not the IP of the originating requester (which would signify that mod_remoteip was doing its job), but instead it is still the IP of the frontend proxy server