Why containers matter in Docker - See It in Action

Why Containers Matter

📖 Scenario: You are a developer who wants to share a simple web app with your friend. But your friend has a different computer setup. You want to make sure the app runs exactly the same on both computers.

🎯 Goal: Build a Docker container that runs a simple web server. This shows how containers keep apps working the same everywhere.

📋 What You'll Learn

Create a Dockerfile that uses the official Python image

Add a simple Python web server script inside the container

Expose port 8000 to access the web server

Run the container and see the web server output

💡 Why This Matters

🌍 Real World

Containers let developers share apps that run the same on any computer, avoiding setup problems.

💼 Career

Understanding containers is key for DevOps roles to deploy and manage applications reliably.

1

Create a simple Python web server script

Create a file named app.py with this exact code: from http.server import SimpleHTTPRequestHandler, HTTPServer server = HTTPServer(('0.0.0.0', 8000), SimpleHTTPRequestHandler) server.serve_forever()

Docker

# Create the app.py file with the Python web server code
# Your code here

Need a hint?

This script starts a simple web server on port 8000 that serves files from the current folder.

2

Write a Dockerfile to containerize the app

Create a file named Dockerfile with these exact lines: FROM python:3.12-slim COPY app.py /app.py EXPOSE 8000 CMD ["python", "/app.py"]

Docker

from http.server import SimpleHTTPRequestHandler, HTTPServer

server = HTTPServer(('0.0.0.0', 8000), SimpleHTTPRequestHandler)
server.serve_forever()

# Create the Dockerfile with the base image, copy, expose, and CMD instructions
# Your code here

Need a hint?

The Dockerfile tells Docker which base image to use, copies your app, opens port 8000, and runs the app.

3

Build the Docker image

Run the exact command docker build -t simple-web . in your terminal to build the Docker image named simple-web.

Docker

from http.server import SimpleHTTPRequestHandler, HTTPServer

server = HTTPServer(('0.0.0.0', 8000), SimpleHTTPRequestHandler)
server.serve_forever()

# Build the Docker image with the tag simple-web
# Your code here

Need a hint?

This command tells Docker to build an image from the current folder and name it simple-web.

4

Run the Docker container and check output

Run the exact command docker run -p 8000:8000 simple-web and then open http://localhost:8000 in your browser. Write SimpleHTTPServer as the output you see in the terminal logs.

Docker

from http.server import SimpleHTTPRequestHandler, HTTPServer

server = HTTPServer(('0.0.0.0', 8000), SimpleHTTPRequestHandler)
server.serve_forever()

# Run the container and check the output
# Your code here

Need a hint?

Running the container starts the web server. The terminal shows SimpleHTTPServer in the logs.