How does nginx look at the backend server (puma, passenger)?

Question

Nginx

How to tell nginx to look at the backend server?
On the example of this config https://www.notion.so/28b5b03a5fc942ef92d449721eae0c5c, for example.
I understand that this is indicated in the directive here upstream, are we just looking puma.sock?
Those. in general, in order for nginx to interact with the backend server, you need to listen .sock?
With passenger the same situation?

Answer 1

A specific puma instance starts up and creates a juice file somewhere, this file is needed for communication.
Now nginx redirects the request from itself, if it matches all the specified conditions in the config, to a specific running puma instance.
There can be many applications on the server. To know which application you need to direct next and use the juice files.
This is a common behavior that needs to be mastered and remembered: not only the cougar and the passenger use this method.