Docker – Introduction

🐳 Docker – Introduction

Docker is a containerization platform that lets you package an application with everything it needs (code, runtime, libraries, configs) into a single unit called a container.

Containers run the same way everywhere — on a laptop, server, or cloud.

“It works on my machine” stops being a problem.

🧱 Key Docker Concepts

1️⃣ Image

• A read-only blueprint for a container
• Built from a Dockerfile
• Example: nginx:latest, node:18

2️⃣ Container

• A running instance of an image
• Lightweight and fast
• Starts in seconds

3️⃣ Dockerfile

A text file that defines how an image is built.

Example:

dockerfile

Copy code

FROM node:18 WORKDIR /app COPY . . RUN npm install CMD ["node", "app.js"]

⚙️ Docker Architecture

• Docker Client – docker CLI
• Docker Engine (Daemon) – Runs containers
• Docker Registry – Stores images (Docker Hub, ECR)

🌍 Why Docker Is Used

✔ Consistent environments

✔ Faster deployments

✔ Lightweight (shares OS kernel)

✔ Easy CI/CD integration

✔ Microservices-friendly