Challenge, Easy,  on  Containers, Programming

Write Your First Dockerfile

In this challenge, you will write your very first Dockerfile to containerize a simplistic Node.js server application.

The application is located in the ~/app/ directory. It's a single server.js file that creates an HTTP server using only Node.js built-in modules - no external dependencies needed.

Take a moment to look at the code before you begin:

cat ~/app/server.js

If you'd like to test the application locally before containerizing it, run the following command:

node ~/app/server.js

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 responds 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 a set of instructions for building a container image - a portable filesystem snapshot that includes the application code and everything needed to run it.

Since the application in this challenge is a single server.js file with no external dependencies, your Dockerfile only needs three instructions:

  • FROM - specify a base image that already has Node.js installed (e.g., node:24-slim)
  • COPY - copy server.js from the host filesystem into the image
  • CMD - specify the command to start the application (e.g., node server.js)

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

Make sure your Dockerfile copies server.js into the image and that the CMD instruction starts the server correctly.

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-first-dockerfile

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

Stream your changes

labctl content push -fw challenge docker-write-first-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