How to implement a gateway for a server?

Question

Nginx

Hello, I need to implement such a system.
There are two servers, one will act as a gateway to the second main server. It is necessary to close the main server as much as possible, that is, all requests to the server will go through the gateway, and the main server will also communicate via the API via the gateway.

My thoughts were:
Install Nginx on the gateway and redirect requests to Nginx on the main server through proxy_pass. And to access other services via API on the gateway server, organize a VPN and all traffic from the main server to pass through the VPN.

How to implement all this with minimal loss of speed?
Maybe there are sensible articles on my topic, how to pass all server traffic through a VPN or some kind of tunnel?
Thank you!