location / {
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header Host $http_host;
    proxy_set_header X-NginX-Proxy true;
    proxy_pass http://172.24.0.3;
}

<?php

echo('HTTP_CLIENT_IP: '.$_SERVER['HTTP_CLIENT_IP']);
echo('<br>HTTP_X_FORWARDE‌​D_FOR'.$_SERVER['HTTP_X_FORWARDE‌​D_FOR']);
echo('<br>REMOTE_ADDR'.$_SERVER['REMOTE_ADDR']);
echo('<br>HTTP_X_FORWARDED'.$_SERVER['HTTP_X_FORWARDED']);
echo('<br>HTTP_FORWARDED'.$_SERVER['HTTP_FORWARDED']);
echo('<br>HTTP_FORWARDED_FOR'.$_SERVER['HTTP_FORWARDED_FOR']);

?>

HTTP_CLIENT_IP:
HTTP_X_FORWARDE‌​D_FOR:
REMOTE_ADDR: 172.24.0.2
HTTP_X_FORWARDED:
HTTP_FORWARDED:
HTTP_FORWARDED_FOR: