Docker Basics

What is Docker?

Docker is a platform for packaging applications and dependencies into containers - isolated, lightweight, and portable environments.

Key Concepts

Concept	Description
Image	Blueprint for creating a container
Container	Running instance of an image
Dockerfile	File defining how to build an image
Volume	Persistent storage for containers
Network	Connectivity between containers

Basic Commands

# Pull image
docker pull node:20-alpine

# Run container
docker run -d -p 3000:3000 --name myapp node:20-alpine

# List containers
docker ps

# Stop & remove
docker stop myapp && docker rm myapp

Dockerfile Example

FROM node:20-alpine
WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production
COPY . .
EXPOSE 3000
CMD ["node", "server.js"]

Docker Compose

services:
  web:
    build: .
    ports:
      - "3000:3000"
    depends_on:
      - db
  db:
    image: postgres:16-alpine
    environment:
      POSTGRES_PASSWORD: secret
    volumes:
      - pgdata:/var/lib/postgresql/data

volumes:
  pgdata:

Note

Docker Desktop requires a paid license for large enterprises. Consider Podman as a free alternative.

Tips

• Use multi-stage builds to reduce image size
• Always use .dockerignore to exclude unnecessary files
• Prefer alpine images for production