Docker// Complete Guide

# ── Stage 1: Builder ─────────────────────────────────────
FROM node:20-alpine AS builder

# Set working directory
WORKDIR /app

# Copy dependency files first (better layer caching)
COPY package*.json ./

# Install dependencies
RUN npm ci --only=production

# Copy source code
COPY . .

# Build the application
RUN npm run build

# ── Stage 2: Production ──────────────────────────────────
FROM node:20-alpine

# Add metadata labels
LABEL maintainer="dev@example.com" version="1.0"

# Create non-root user for security
RUN addgroup -S appgroup && adduser -S appuser -G appgroup

WORKDIR /app

# Copy only production build from builder stage
COPY --from=builder --chown=appuser:appgroup /app/dist ./dist
COPY --from=builder --chown=appuser:appgroup /app/node_modules ./node_modules

# Set environment variables
ENV NODE_ENV=production PORT=3000

# Build-time argument
ARG BUILD_VERSION
ENV BUILD_VERSION=$BUILD_VERSION

# Declare volume for logs
VOLUME ["/app/logs"]

# Document the port
EXPOSE 3000

# Switch to non-root user
USER appuser

# Health check
HEALTHCHECK --interval=30s --timeout=10s --retries=3 \
  CMD wget -qO- http://localhost:3000/health || exit 1

# Default entrypoint
ENTRYPOINT ["node"]

# Default command (can be overridden)
CMD ["dist/server.js"]

# Dependencies
node_modules/
# VCS
.git/
.gitignore
# Build artifacts
dist/
build/
*.log
# Secrets
.env
.env.*
*.pem
# Docker files themselves
Dockerfile*
docker-compose*

name: myapp

services:

  frontend:
    build:
      context: ./frontend
      target: production
    ports:
      - "3000:3000"
    environment:
      - REACT_APP_API_URL=http://localhost:8080
    depends_on:
      - api
    networks:
      - frontend-net

  api:
    build: ./backend
    ports:
      - "8080:8080"
    environment:
      - DATABASE_URL=postgres://user:pass@db:5432/mydb
      - REDIS_URL=redis://cache:6379
    depends_on:
      db:
        condition: service_healthy
      cache:
        condition: service_started
    networks:
      - frontend-net
      - backend-net
    restart: unless-stopped

  db:
    image: postgres:16-alpine
    volumes:
      - postgres_data:/var/lib/postgresql/data
      - ./init.sql:/docker-entrypoint-initdb.d/init.sql
    environment:
      POSTGRES_DB: mydb
      POSTGRES_USER: user
      POSTGRES_PASSWORD: pass
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U user"]
      interval: 10s
      timeout: 5s
      retries: 5
    networks:
      - backend-net

  cache:
    image: redis:7-alpine
    command: redis-server --appendonly yes
    volumes:
      - redis_data:/data
    networks:
      - backend-net

volumes:
  postgres_data:
  redis_data:

networks:
  frontend-net:
    driver: bridge
  backend-net:
    driver: bridge
    internal: true  # no external access

docker compose up          # Start all services
docker compose up -d       # Start in detached mode
docker compose down        # Stop and remove containers
docker compose down -v    # Also remove volumes
docker compose ps          # List service containers
docker compose logs -f    # Follow all logs
docker compose build       # Build all service images
docker compose pull        # Pull latest images
docker compose restart api # Restart specific service
docker compose exec db psql # Exec into service
docker compose scale api=3 # Scale a service to 3 replicas
docker compose config      # Validate and print config

# Create a custom bridge network
docker network create --driver bridge myapp-net

# Run containers on the same network
docker run -d --name db --network myapp-net postgres
docker run -d --name api --network myapp-net myapi

# Containers can now reach each other by name:
# api connects to db using hostname "db"

# Port mapping: HOST_PORT:CONTAINER_PORT
docker run -p 8080:80 nginx        # TCP only
docker run -p 53:53/udp dns-server  # UDP port
docker run -P nginx               # Auto-assign all EXPOSED ports

# Connect existing container to another network
docker network connect mynet mycontainer

# Inspect network details
docker network inspect myapp-net

# ── Named Volumes ────────────────────────────────────────
docker volume create pgdata
docker run -v pgdata:/var/lib/postgresql/data postgres

# ── Bind Mounts ──────────────────────────────────────────
# Mount current directory into container (dev mode)
docker run -v $(pwd):/app -w /app node npm start

# Read-only bind mount
docker run -v /host/config:/app/config:ro myapp

# ── tmpfs Mounts ─────────────────────────────────────────
docker run --tmpfs /run:rw,noexec,nosuid,size=65536k myapp

# ── Backup a Named Volume ────────────────────────────────
docker run --rm -v pgdata:/data -v $(pwd):/backup alpine \
  tar czf /backup/pgdata-backup.tar.gz /data

# ── Share volume between containers ──────────────────────
docker run -d --name writer -v shared:/data writer-app
docker run -d --name reader --volumes-from writer reader-app

# ── Volume management ────────────────────────────────────
docker volume ls
docker volume inspect pgdata
docker volume prune          # Remove unused volumes