When apache is running behind the proxy server it shows the IP of the proxy server as visitor IP. To fix this, you need to enable Apache module remoteip.
https://httpd.apache.org/docs/2.4/mod/mod_remoteip.html
On Ubuntu/Debian, this can be enabled with the command
a2enmod remoteip
Now create file
vi /etc/apache2/conf-available/remoteip.conf
Add
RemoteIPHeader X-Forwarded-For RemoteIPTrustedProxy IP_OF_YOUR_PROXY_SERVER_HERE
IP_OF_YOUR_PROXY_SERVER_HERE = repace with your proxy server. This can be any proxy server like haproxy, nginx, etc.. If you have more than one proxy server, use IPs separated by space.
If your proxy IP is internal, use RemoteIPInternalProxy instead of RemoteIPTrustedProxy. On a server running varnish, RMOTE_ADDR shows 127.0.0.1 (varnish IP). To fix this, I used following
RemoteIPHeader CF-Connecting-IP RemoteIPInternalProxy 127.0.0.1
CF-Connecting-IP is because the site was behind cloudflare. Use X-Forwarded-For instead of CF-Connecting-IP if not using cloudflare.
Enable config with
a2enconf remoteip
To get Apache Logs to show real Visitor IP, replace %h with %a in LogFormat.
On Ubuntu
vi /etc/apache2/apache2.conf
Find
LogFormat "%h %l %u %t \"%r\" %>s %O \"%{Referer}i\" \"%{User-Agent}i\"" combined
Replace with
LogFormat "%a %l %u %t \"%r\" %>s %O \"%{Referer}i\" \"%{User-Agent}i\"" combined
Restart Apache with
systemctl restart apache2
Now apache/php will show proper visitor IP instead of proxy server IP.