Get real user ip address while using cloudflare

You, probably, are looking for this: $_SERVER["HTTP_CF_CONNECTING_IP"]

or

$ip = $_SERVER["HTTP_CF_CONNECTING_IP"] ?? $_SERVER["X-Forwarded-For"] ?? $_SERVER['REMOTE_ADDR'];

As cloudflare proxies requests through it's own servers, $_SERVER['REMOTE_ADDR'] shows ip address of one of cloudflare servers, not the real user.

Cloudflare adds several additional headers to requests and responses. The HTTP_CF_CONNECTING_IP one has real user ip.

with nginx config

If you want to solve problem as system administrator, check out nginx solution. It uses ngx_http_realip_module.

with yii2

If you are using Yii2, modify your web-config (default is config/web.php) and add ipHeaders param to request as follows:

'request' => [
    'ipHeaders' => [
        'CF-Connecting-IP',
        'X-Forwarded-For',
    ],
],

X-Forwarded-For is default header used by Yii, I recommend to leave it as is.