Why doesn't $_SERVER['SERVER_NAME'] return everything?

Question

PHP

I am writing a router, I ran into the following problem:
when trying to return a subdomain, the function for some reason returns the main domain, but it does not see the subdomain. That is, when you try to do this on a site like: sub.domain.com

$sub = explode('.', $_SERVER['SERVER_NAME']);
echo $sub[0];

The $sub array contains domain and com, but there is no sub. I don’t understand what could be the matter, since with the same code on apache everything was in order.

Answer 1

serverfault.com/questions/496597/php-fpm-server-na...
use $_SERVER['HTTP_HOST']