SocketIO how to communicate between servers?

Question

JavaScript

Good evening! Could you tell me (
For example, there is an Nginx balancer and several NodeJS servers on different hosts.
The SocketIO documentation says that in nginx, you need to use ip_hash to assign a cookie, and already in NodeJS you need to connect an adapter, so

var io = require('socket.io')(3000);
var redis = require('socket.io-redis');
io.adapter(redis({ host: 'localhost', port: 6379 }));

But I have a question:
If I, as an example, at the office. I’ll specify the host site as local, then socketio will not know about other nodejs servers (
Then do I understand correctly that I need to create another server for Redis and specify the ip of this particular server in the host parameter?