index.js

const express = require('express');
const mongoose = require('mongoose');
const bodyParser = require('body-parser');
const path = require('path');
const cluster = require('cluster');
const numCPUs = require('os').cpus().length;

const isDev = process.env.NODE_ENV !== 'production';
const PORT = process.env.PORT || 5000;

// Multi-process to utilize all CPU cores.
if (!isDev && cluster.isMaster) {
	console.error(`Node cluster master ${process.pid} is running`);

	// Fork workers.
	for (let i = 0; i < numCPUs; i++) {
		cluster.fork();
	}

	cluster.on('exit', (worker, code, signal) => {
		console.error(`Node cluster worker ${worker.process.pid} exited: code ${code}, signal ${signal}`);
	});

} else {
	const app = express();

	// Bodyparser Middleware
	app.use(bodyParser.json());

	// DB config
	const db = require('./config/keys').mongoURI;

	// Connect to mongo
	mongoose
		.connect(db, { useUnifiedTopology: true, useNewUrlParser: true, useCreateIndex: true, useFindAndModify: false })
		.then(() => console.log('MongoDB Connected...'))
		.catch(err => console.error(err));

	// Use Routes
	const User = require('./routes/api/user')
	const Workout = require('./routes/api/workout')
	const Exercise = require('./routes/api/exercise')
	app.use('/api/user', User);
	app.use('/api/workout', Workout);
	app.use('/api/exercise', Exercise);

	// Priority serve any static files.
	app.use(express.static(path.resolve(__dirname, '../react-ui/build')));

	// Answer API requests.
	app.get('/api', function (req, res) {
		res.set('Content-Type', 'application/json');
		var str = ('{"message":"Hello from the custom server!'.concat(Math.random())).concat('"}');
		res.send(str);
	});

	// All remaining requests return the React app, so it can handle routing.
	app.get('*', function (request, response) {
		response.sendFile(path.resolve(__dirname, '../react-ui/build', 'index.html'));
	});

	app.listen(PORT, function () {
		console.error(`Node ${isDev ? 'dev server' : 'cluster worker ' + process.pid}: listening on port ${PORT}`);
	});
}