Documentation for reverse proxy using NGINX / APACHE

[JasonTheDynamite]

Describe your motivation

Currently I am trying to configure VAADIN with NGINX + CloudFlare. Requests which end with "?v=rheartbeat&uiId=0" fail with 403 forbidden or other errors. Getting to event this point was a disaster. 7 day disaster of constant try & fail. I wanted to achieve simple reverse proxy using proxy_pass from NGINX to change subdomain in URL.
If I turn off NGINX everything works. ☹️ There is absolutely no help on the internet regarding this subject.

Describe the solution you'd like

Precise EXACT documentation with examples for NGINX & Apache

Describe alternatives you've considered

No alternatives. This has to be made,

Additional context

Do it please ASAP

[mcollovati]

Closing as this is a duplicate of vaadin/docs#1776

@JasonTheDynamite please add your comments and notes on that ticket