Docker 101: What, Why, How & Case Study

February 1, 2025

Docker Container

Docker has revolutionized software development by making applications portable, scalable, and consistent across environments. But what exactly is Docker, and why has it become indispensable for developers? Let’s break it down.

🐋 What is Docker?

Docker is an open-source platform for developing, shipping, and running applications inside lightweight, portable containers. Unlike virtual machines (VMs) that emulate entire operating systems, Docker containers share the host OS but isolate applications and their dependencies. Think of it like this:

  • VMs are like shipping entire houses (OS + app), while
  • Docker containers are like shipping only the furniture (app + dependencies).

This makes containers faster, smaller, and more resource-efficient. Docker’s core components include:

  1. Docker Engine: The runtime that builds, runs, and manages containers.
  2. Dockerfile: A blueprint for creating container images.
  3. Docker Hub: A registry to store and share container images.

🤔 Why Use Docker?

Docker solves three major pain points in software development:

  1. "It works on my machine" syndrome
    Containers bundle code and dependencies, ensuring apps run identically across environments (dev, staging, production).

  2. Scalability & Efficiency
    Containers launch in seconds and share the host OS, reducing overhead compared to VMs.

  3. Portability
    Build once, run anywhere—on laptops, servers, or clouds (AWS, Azure, GCP).

Use Cases:

  • Microservices architecture (e.g., Netflix, Uber).
  • CI/CD pipelines (automate testing/deployment).
  • Legacy app modernization.

⚙️ How Does Docker Work?

Docker’s workflow follows three steps:

  1. Build
    Developers write a Dockerfile to define the app’s environment (OS, libraries, code). Docker builds this into an image. 

    # Sample Dockerfile for a Node.js app
FROM node:18
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
CMD ["npm", "start"]