Node.js + Express.js + Socket.io on port 443 (HTTPS TLS/SSL)

I have an app with Node.js, Express.js, and Socket.io that runs fine using ANY port except 443. The server is meant to only operate over HTTPS port 443 and likewise, the websocket should be encrypted as well.

CODE THAT WORKS

var fs = require('fs');
var https = require('https');
var express = require('express');
var socket = require('socket.io');
var sslOptions = {
    key: fs.readFileSync(__dirname + '/../ssl/server.key,
    cert: fs.readFileSync(__dirname + '/../ssl/server.pem,
    ciphers: 'ECDHE-RSA-AES256-SHA:AES256-SHA:RC4-SHA:RC4:HIGH:!MD5:!aNULL:!EDH:!AESGCM',
    honorCipherOrder: true
};

var app = express();
var server = https.createServer(sslOptions, app);
var io = socket.listen(server, {
    "log level" : 3,
    "match origin protocol" : true,
    "transports" : ['websocket']
});
server.listen(8443);

When I change the port (last line) to 443, the Node server crashes right away with an error:

warn: error raised: Error: listen EADDRINUSE

Copyright Notice：Content Author:「Justin Elkow」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/22725717/node-js-express-js-socket-io-on-port-443-https-tls-ssl