Assignment #4: Application Containerization

This is a simple Node.js web application designed for learning Docker containerization concepts.

Application Overview

This application is a basic Express.js web server that:

• Serves a static HTML page at the root (/)
• Provides an API status endpoint at /api/status
• Includes a health check endpoint at /health
• Runs on port 3000 by default (configurable via PORT environment variable)

What's Included

• app.js: Main application server file
• package.json: Node.js dependencies and project configuration
• public/index.html: Static HTML page that confirms successful containerization
• public/style.css: Styling for the web page

Running Without Docker (for reference only)

If you wanted to run this application directly (not required for assignment):

npm install
npm start

Your Docker Assignment

DO NOT MODIFY THE APPLICATION CODE

Your task is to containerize this existing application using Docker. You need to:

1. Create a Dockerfile that properly containerizes this Node.js application
2. Build a Docker image from your Dockerfile
3. Run a container from your image
4. Verify the application works by accessing it in your browser

Starting the Application

• To build the docker image run the command:

• To run your docker container in port 3000 run the command:

Reflection Question

Answer the following question in the space below: How does containerization with Docker differ from using virtual machines, and why might a development team choose Docker containers over VMs for deploying applications like the one you just containerized?

Application Requirements for Docker

Your Dockerfile should ensure:

• The application has Node.js runtime available
• All application files are copied into the container
• Dependencies are installed (npm install)
• Port 3000 is exposed
• The application starts with npm start
• The container can be accessed from your host machine

Verification

When your Docker container is running correctly:

• Navigate to http://localhost:3000 (or whatever port you mapped)
• You should see a success page confirming containerization worked
• The /api/status endpoint should return JSON status information

Troubleshooting Tips

• Make sure your port mapping is correct in the docker run command
• Check that all files are copied into the container
• Verify Node.js dependencies are installed in the container
• Use docker logs <container-name> to see application output

File Structure Expected

docker-assignment/
├── Dockerfile          # You create this
├── app.js              # Provided
├── package.json        # Provided
├── public/             # Provided
│   ├── index.html      # Provided
│   └── style.css       # Provided
└── README.md           # This file

Good luck with your Docker containerization!