Node - acting as a Webserver and a client - node.js

Question

When users do a GET /check/health, this client should talk to Server and sever should give the client the answer..
But the message from the server is not received on the client..
Client side - also acting as a webserver
var io = require('socket.io-client');
var socket = io.connect('http://localhost:4000', {reconnect: true});
var express = require('express');
var app= express();
var path = require('path');
var bodyParser= require('body-parser');
app.use(express.static(__dirname+"/public/"));
app.use(bodyParser.json());
app.set('views',path.join(__dirname,'/public/html'));
app.engine('html', require('ejs').renderFile); //specify which template engine to use
app.set('view engine', 'ejs');
app.get('/check/health',function(req,res){
//console.log('Connected Success!!');
socket.on('connect', function(socket) {
console.log('Connected!');
});
socket.emit('data', 'I need your health status');
socket.on('data', function(data) {
console.log('Message from monitoring is : ' + ': ' + data);
});
socket.on('server data', function(data) {
console.log('Received server data: ' + data);
});
});
app.listen(3000);
console.log("Server running at http://localhost:3000/'");
Server side:
var app = require('express')();
var SERVER = require('http').Server(app);
var io = require('socket.io')(SERVER);
var express = require('express');
var mongoose = require('mongoose');
mongoose.connect('mongodb://localhost/sensor_db');
io.on('connection', function(socket){
console.log('connection received from Provisioning ');
// To get messages from Provisioning server
socket.on('data', function(data) {
console.log('Message from provision is : ' + ': ' + data);
});
socket.emit('server data', 'Here is yiour data - 1111');
});
SERVER.listen(4000, function(){
console.log('listening on *:4000');
});

Answer 1

There are a number of potential issues here, but the main one is that your server side code is missing the following very important line:
http.listen(4000);
Adding that should get you started down the right path. Also, I would suggest renaming the http variable to something else, since it's not the http module. server makes more sense to me.
Here's a more minimal example of what you're looking to do. It's missing a few things such as error handling, considering what should happen when a request to /check/health comes in and your socket.io connection isn't up, etc, but I'll leave that as an exercise for you. I also trimmed out some stuff that wasn't relevant to the question (mongoose, ejs templating, etc), so you'll have to add those back in when you're confident that this piece is working as intended.
Client Side
var io = require('socket.io-client');
var socket = io.connect('http://localhost:4000', { reconnect: true });
var express = require('express');
var app= express();
var path = require('path');
// careful here -- the socket.io connection will be made
// outside of the context of the /check/health callback,
// so you should move the connect event handler out here.
socket.on('connect', function(socket) {
console.log('Connected!');
});
app.get('/check/health',function(req,res){
// note the third argument here,
// which can be used as an acknowledgement from the server
// that your client's emit was received
socket.emit('data', 'I need your health status', function ack(data) {
console.log('data emit was acknowledged:', data);
// make sure you send something back to the requester
// or they'll just hang until timeout
return res.json(data);
});
// if you want, you could technically use socket.once('server data'),
// in this location, but this is probably going to be closer
// to the style of communication you actually want --
// which is one response to this specific single socket emit.
});
app.listen(3000);
console.log('Server listening at port 3000');
Server Side
var app = require('express')();
var server = require('http').Server(app);
var io = require('socket.io')(server);
var express = require('express');
io.on('connection', function(socket){
console.log('connection received from Provisioning');
// To get messages from Provisioning server
socket.on('data', function(data, ack) {
console.log('Message from provision is : ' + ': ' + data);
ack('here is your data - 1111');
});
});
server.listen(4000, function(){
console.log('socket.io server listening on *:4000');
});