How it works....

There's only one main block directive to get our simple test working, with a few key areas.

proxy_pass http://127.0.0.1:3000; 

The proxy will forward the connection back to our Express-driven test application, which we configured to listen on port 3000 of the localhost.

proxy_http_version 1.1; 

By default, proxied connections back to the Node.js application will be HTTP/1.0 only. Setting this to HTTP/1.1 allows the use of keep-alive, which means the connection between NGINX and the application remains open rather than establishing a new connection every time. On a heavily loaded system, this is much more efficient.

proxy_set_header Upgrade $http_upgrade; 
proxy_set_header Connection "upgrade"; 

The WebSocket protocol uses the Upgrade and Connection headers as part of the handshake process. We need to set this at the NGINX level in order to allow the handshake process to work as expected. As it's compatible with HTTP/1.1, it won't interfere with the standard connections either.