Containers & Images

TL;DR

• Image = blueprint (immutable). Container = running instance.
• Dockerfile → docker build → Image → docker run → Container.
• Layers are cached. Order Dockerfile commands from least→most changing.

Essential Commands

# Images
docker build -t myapp .              # Build from Dockerfile
docker images                         # List images
docker rmi myapp                      # Remove image

# Containers
docker run -d -p 3000:3000 myapp     # Run detached, map port
docker ps                             # List running containers
docker ps -a                          # Include stopped
docker stop <id>                      # Stop gracefully
docker rm <id>                        # Remove container
docker logs <id>                      # View logs
docker exec -it <id> sh              # Shell into container

Dockerfile (Node.js)

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

Docker Compose

# docker-compose.yml
services:
  app:
    build: .
    ports: ["3000:3000"]
    environment:
      - DATABASE_URL=postgres://user:pass@db:5432/mydb
    depends_on: [db]

  db:
    image: postgres:16-alpine
    environment:
      POSTGRES_PASSWORD: pass
      POSTGRES_DB: mydb
    volumes: [pgdata:/var/lib/postgresql/data]

volumes:
  pgdata:

Quick Reference