🐳 Getting Started with Docker: Images, Containers & Dockerfile Basics (2025)

📌 What is Docker?

Docker is an open-source platform that lets you package your applications and dependencies into a standardized unit called a container. Containers are lightweight, fast, and portable — like mini virtual machines, but without the heavy baggage.

Think of Docker containers as isolated sandboxes where your app always behaves the same — no more “works on my machine” drama!

🆚 Docker vs Virtual Machines

Aspect	Docker	Virtual Machines
Startup Time	⚡ Milliseconds	⏳ Minutes
Resource Usage	💡 Low	🔋 High
Isolation Level	Medium (OS shared)	High (Own OS)

⚙️ Components of Docker

Docker Engine: Core service that builds, runs, and manages containers.
Docker CLI: Command-line tool to interact with Docker (e.g., docker run).
Docker Desktop: GUI + CLI for managing Docker on Windows/macOS (includes Docker Engine).
Docker Hub: Public registry where you can find and pull container images.

🧪 Running Your First Docker Container

Let's run the classic Hello World container:

docker run hello-world

This pulls the hello-world image from Docker Hub and runs it as a container. You should see:

Hello from Docker!
This message shows that your installation appears to be working correctly.

📦 Dockerfile: Building Your Own Image

Let's say you have a simple Node.js app. Here's how you can write a Dockerfile:

# Dockerfile
FROM node:18-alpine
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
EXPOSE 3000
CMD ["node", "index.js"]

To build this image:

docker build -t my-node-app .

To run the container:

docker run -p 3000:3000 my-node-app

🐍 Python Version (Bonus)

If you prefer Python, here's a minimal Flask app app.py and Dockerfile:

# app.py
from flask import Flask
app = Flask(__name__)

@app.route("/")
def hello():
    return "Hello from Docker!"

if __name__ == "__main__":
    app.run(host="0.0.0.0", port=5000)

# Dockerfile
FROM python:3.11-alpine
WORKDIR /app
COPY requirements.txt .
RUN pip install -r requirements.txt
COPY . .
EXPOSE 5000
CMD ["python", "app.py"]

🧱 Image & Container Lifecycle

Build Image: docker build -t name .
Run Container: docker run -d -p host:container name
List Running: docker ps
Stop Container: docker stop CONTAINER_ID
Remove Container: docker rm CONTAINER_ID
Remove Image: docker rmi IMAGE_ID

🔍 Pulling Images from Docker Hub

Docker Hub is like GitHub for containers. To pull a ready-to-use image:

docker pull nginx
docker pull mongo
docker pull python:3.11

Then run them like this:

docker run -d -p 8080:80 nginx

🧠 Pro Tips for Beginners

Use docker ps -a to see all containers (even stopped).
Add --rm to auto-remove containers after they stop.
Use .dockerignore (like .gitignore) to skip files during build.
Tag images with versions: docker build -t myapp:v1 .

🎯 Summary

You've just walked through the basics of Docker — from containers and images to building your first Dockerfile. Whether you're building in Node.js or Python, Docker keeps your environment clean and consistent.

In our next post, we'll dive into 🔗 (Post 2): Docker Volumes & Networks: Managing Data & Communication!

— Blog by Aelify (ML2AI.com)

📚 Documentation Index