The App

For this guide, we'll use a simple Node.js app as an example, but the same principles can be applied to any app:

const express = require('express');

// Constants
const PORT = 8080;
const HOST = '0.0.0.0';

// App
const app = express();
app.get('/simple-web-app', (req, res) => {
  res.send('Hello world\n');
});

app.listen(PORT, HOST);
console.log(`Running on http://${HOST}:${PORT}`);

That's it! It's a classic express "Hello World" starter app that listens for requests on port 8080. For this example walkthrough, save this file as server.js.

Since we need to pull in the dependencies to run this app, we will also need a corresponding package.json:

{
  "name": "docker_web_app",
  "version": "1.0.0",
  "main": "server.js",
  "scripts": {
    "start": "node server.js"
  },
  "dependencies": {
    "express": "^4.16.1"
  }
}