What Is Docker?

Docker packages your application with all dependencies into a container. Ensures consistent behavior across development, testing, and production environments.

Dockerfile

FROM node:18-alpine

WORKDIR /app

COPY package*.json ./
RUN npm install

COPY . .

EXPOSE 3000
CMD ["npm", "start"]

Essential Commands

# Build the image
docker build -t my-app .

# Run a container
docker run -p 3000:3000 my-app

# List containers
docker ps

# Stop container
docker stop container_id

docker-compose

version: '3.8'
services:
  app:
    build: .
    ports:
      - "3000:3000"
  db:
    image: postgres:15
    environment:
      POSTGRES_PASSWORD: secret

Conclusion

Docker eliminates "works on my machine" problems forever. Essential for modern development and deployment workflows.