Write a Dockerfile That Excludes Dev Dependencies from the Production Image

In this challenge, you will write a Dockerfile to containerize a Node.js web application without including its development dependencies in the final image.

Explore the application

The application is located in the ~/app/ directory. It's an Express.js web server with a couple of API endpoints. Take a moment to look at the package.json:

cat ~/app/package.json

Notice that it has both dependencies and devDependencies sections. The runtime dependency is just express - the web framework the app needs to serve requests. The devDependencies include tools that are only useful during development:

ESLint (eslint, @eslint/js, globals) - a linter
Jest (jest) - a testing framework
Supertest (supertest) - an HTTP testing library
Nodemon (nodemon) - a dev server that auto-restarts on file changes

You can try them out by first installing all the dependencies:

cd ~/app && npm install

Then running the linter:

npm run lint

And the tests:

npm run test

These tools are essential during development, but the production container only needs to run node server.js - and for that, only express is required. Including linters, test frameworks, and their transitive dependencies in the image would add hundreds of unnecessary packages and tens of megabytes of bloat.

The task

Your goal is to:

Create a Dockerfile in the ~/app/ directory.
Build a Docker image named my-app:v1.0.0.
Ensure the containerized application starts correctly and responds on port 3000.
Make sure the image does not contain any dev dependencies.

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 with instructions for building a container image.

Your Dockerfile needs at least the following instructions:

FROM - specify a base image (e.g., node:24-slim)
COPY - copy the application files into the image
RUN - install the application dependencies using npm
CMD - specify the command to start the server

Container image composition and the main factors that affect it.

Hint 2

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

Build and Publish a Container Image With Docker

Hint 3

If the container fails to start or the application doesn't respond, run the container in the foreground to see the error:

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

Make sure the application dependencies are installed inside the image and the server process starts correctly.

Hint 4

By default, npm ci and npm install install all dependencies, including devDependencies like linters and test frameworks. However, both commands provide ways to explicitly exclude (or include) specific dependencies.

Check out the npm ci and npm install documentation for more details.

Start challenge