Challenge, Easy,  on  Containers, Programming

Write a Dockerfile for a Simple Web Server Application

In this challenge, you will write a Dockerfile from scratch to containerize a Node.js web application built with Express.js.

The application is located in the ~/app/ directory. It's a simple web server that serves a couple of HTML pages and exposes a REST API with a few endpoints. Take a moment to explore the code and file structure before you begin.

If you'd like to test the application locally before containerizing it, run the following commands from the ~/app/ directory:

  1. npm install - install the dependencies
  2. npm start - start the application server

Then open a second terminal and verify the application works:

curl localhost:3000

curl localhost:3000/api/health

Your goal is to:

  1. Create a Dockerfile in the ~/app/ directory.
  2. Build a Docker image named my-app:v1.0.0.
  3. Ensure the containerized application starts correctly and serves all pages and API endpoints on port 3000.

You can test your image at any point by running:

docker run -p 3000:3000 my-app:v1.0.0
Hint 1

A Dockerfile is a text file that contains instructions for building a Docker image - a portable filesystem snapshot that includes the application code and all its dependencies.

At minimum, your Dockerfile needs the following instructions:

  • FROM - specify a base image (e.g., node:24-slim)
  • COPY - copy your application files into the image
  • RUN - run the npm install (or better yet, npm ci) command to install the dependencies
  • CMD - specify the command to start the application server

Check out the Dockerfile reference for more details.

Container image composition and the main factors that affect it.
Hint 2

For a refresher on how to build a Docker image, check out this challenge:

Build and Publish a Container Image With Docker

Hint 3

If the container fails to start or the containerized application doesn't respond, run the container in the foreground - it may shed some light on the issue:

docker run -p 3000:3000 my-app:v1.0.0

Double-check that the npm install (or npm ci) command is executed in the Dockerfile to install the application dependencies, and make sure the server process is up and running inside the container.

How to Author Challenges on iximiuz Labs

Instead of providing a subpar online editing experience, iximiuz Labs offers a helper CLI tool called labctl, allowing you to use your favorite text editor (or a full-featured IDE) to write content from the comfort of your local machine.

Install labctl CLI

curl -sf https://labs.iximiuz.com/cli/install.sh | sh

This will download and install the latest version of the labctl CLI. You only need to do this once per workstation.

Authorize labctl

labctl auth login

This will open a browser window asking you to authorize labctl to access your account. You need to do it after a fresh install of labctl and repeat it whenever the auth session expires.

Pull challenge content

labctl content pull challenge docker-write-simple-dockerfile

This will create a local copy of the challenge content in a directory named docker-write-simple-dockerfile. You only need to do this once per challenge.

Stream your changes

labctl content push -fw challenge docker-write-simple-dockerfile

Run this command in a separate terminal to continuously upload your changes to the server while editing the challenge in your favorite text editor or IDE.

You can also use labctl to create, list, and delete your content. Learn more about the available commands: labctl content --help

Start challenge