How are services discovered by web servers?

Question

Nginx

Hey!
Children explain how there is a "discovery of services" by servers?
I so understand it somehow sideways concerns a remote procedure call?
Thanks for answers!

Answer 1

What are you talking about?
About it?
https://habr.com/post/266139/
Or about that?
https://ru.wikipedia.org/wiki/DNS

Answer 2

Open IP ports are scanned. Google nmap.