feat: Make server concurrent (multi-process)

Signed-off-by: Richie Bendall <richiebendall@gmail.com>

server.js

@@ -5,19 +5,22 @@ IMPORTANT:   Set the `github_token` environment variable to a personal access to
 Server port: The `PORT` environment variable can also be set to control the port the server
              should be hosted on.
 */
-
 const express = require('express');
 const minify = require('express-minify');
 const postcssMiddleware = require('postcss-middleware');
 const tmpdir = require('os').tmpdir();
 const path = require('path');
+const cluster = require('cluster');
+const numCPUs = require('os').cpus().length;
 
 // Server
 var PORT = process.env.PORT || 8080;
 
 // Prepare application
 const app = express();
-app.use(minify({ cache: tmpdir }));
+app.use(minify({
+  cache: tmpdir
+}));
 app.set('views', path.join(__dirname, '/licenses'));
 app.set('view engine', 'ejs');
 
@@ -45,7 +48,9 @@ app.use(
 // CORS
 app.use(require('./middleware/cors'));
 // Parse URL-encoded bodies (as sent by HTML forms)
-app.use(express.urlencoded({ extended: true }));
+app.use(express.urlencoded({
+  extended: true
+}));
 // Parse JSON bodies (as sent by API clients)
 app.use(express.json());
 
@@ -57,7 +62,20 @@ app.use(require('./middleware/load-options'));
 app.post('/', require('./routes/post'));
 app.get('/*', require('./routes/get'));
 
-// Start listening for HTTP requests
-app.listen(PORT, () => {
-  console.log(`🚀 on http://localhost:${PORT}`);
-});
+// If the current process is the main one
+if (cluster.isMaster) {
+  // Create processes relative to amount of CPUs
+  Array.from({
+    length: numCPUs
+  }, () => cluster.fork());
+
+  // When worker closed
+  cluster.on('exit', worker => {
+    console.log(`❌ Worker ${worker.process.pid} died.`);
+  });
+} else {
+  // Start listening for HTTP requests
+  app.listen(PORT, () => {
+    console.log(`🚀 on http://localhost:${PORT}`);
+  });
+}