Connection via socket between servers

I have studied communication between two (or more) servers raised in NodeJS via REST más as I searched for content (references, explanations, benchmarks, etc.) I found indications of REST would bring more cost to the process and WebSocket would be more recommended, but all material I found was referring to client (front-end) for server (backend).

The very succinct question is: How to connect and exchange messages between two servers via sockets (backend only)?

The initial implementation where I used REST worked with express to map routes and superagent to make requests.

Now when I try to use WebSocket I'm using the uws module

example.js

var WebSocketServer = require('uws').Server;
var wss = new WebSocketServer({ port: 3000 });

function onMessage(message) {
    console.log('received: ' + message);
}

wss.on('connection', function(ws) {
    ws.on('message', onMessage);
    ws.send('something');
});