Socket.io trigger events between two node.js apps?

I have two servers, one for the back end app, and one that serves the front end. They are abstracted, but share the same database, I have a need for both to communicate real time events between each other using socket.io.

Front end

// serves a front end website
var appPort  = 9200; 

var express  = require('express');
var app      = express();
var http     = require('http');
var server   = http.createServer(app);
var io       = require('socket.io').listen(server);

io.sockets.on('connection', function(socket) {

    socket.on('createRoom', function(room) {
        socket.join(room); // use this to create a room for each socket (room) is from client side
    });

    socket.on('messageFromClient', function(data) {
        console.log(data)
        socket.broadcast.to(data.chatRoom).emit('messageFromServer', data);
    });


});

Back end

//Serves a back end app
var appPort  = 3100; 

var express  = require('express');
var app      = express();
var http     = require('http');
var server   = http.createServer(app);
var io       = require('socket.io').listen(server);

io.sockets.on('connection', function(socket) {

    socket.on('createRoom', function(room) {
        socket.join(room); // use this to create a room for each socket (room) is from client side
    });

    socket.on('messageFromClient', function(data) {
        console.log(data)
        socket.broadcast.to(data.chatRoom).emit('messageFromServer', data);
    });


});

As an admin I want to log in to my back end where I can see all the people logged in, there I can click on whom I would like to chat with.

Say they are logged in to the front end website, when the admin submits a message client side they trigger this socket.emit('messageFromClient', Message); how can I trigger messageFromClient on the front end using port 9200 submitting from the backend port 3100?

You really dont need to start the socket.io server in the front end for this use case.

The way you can get it to work is :

Keep the backend as it is, which acts as a Socket.IO server
In the font end connect to the server using a Socket.IO client.

You can install the client by calling

npm install socket.io-client

and then connect to the server using :

var io = require('socket.io-client'),
socket = io.connect('localhost', {
    port: 3100
});
socket.on('connect', function () { console.log("socket connected"); });
socket.emit('messageFromClient', { user: 'someuser1', msg: 'i am online' });

You can then create a map of socket objects with their corresponding username and send a message to that user based on your business logic.

More Information :

You may have to add cases like client disconnection etc. You can read more about the call backs for that here :

https://github.com/Automattic/socket.io-client