Docker Containerization Best Practices

# Docker Containerization Best Practices

Master Docker containerization with Google Antigravity IDE. This comprehensive guide covers multi-stage builds, security hardening, and production optimization for containerized applications.

## Why Docker?

Docker provides consistent development and deployment environments. Google Antigravity IDE's Gemini 3 engine offers intelligent Dockerfile optimization and security recommendations.

## Multi-Stage Dockerfile

```dockerfile
# Stage 1: Dependencies
FROM node:20-alpine AS deps
WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production && npm cache clean --force

# Stage 2: Build
FROM node:20-alpine AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci
COPY . .
RUN npm run build

# Stage 3: Production
FROM node:20-alpine AS runner
WORKDIR /app

ENV NODE_ENV=production
ENV PORT=3000

# Security: Run as non-root user
RUN addgroup --system --gid 1001 nodejs && \
    adduser --system --uid 1001 nextjs

# Copy only necessary files
COPY --from=deps /app/node_modules ./node_modules
COPY --from=builder /app/.next/standalone ./
COPY --from=builder /app/.next/static ./.next/static
COPY --from=builder /app/public ./public

# Set correct permissions
RUN chown -R nextjs:nodejs /app
USER nextjs

EXPOSE 3000
HEALTHCHECK --interval=30s --timeout=3s --start-period=5s \
  CMD wget --no-verbose --tries=1 --spider http://localhost:3000/api/health || exit 1

CMD ["node", "server.js"]
```

## Docker Compose Configuration

```yaml
# docker-compose.yml
version: "3.9"

services:
  app:
    build:
      context: .
      dockerfile: Dockerfile
      target: runner
    ports:
      - "3000:3000"
    environment:
      - DATABASE_URL=postgresql://postgres:password@db:5432/app
      - REDIS_URL=redis://redis:6379
    depends_on:
      db:
        condition: service_healthy
      redis:
        condition: service_started
    restart: unless-stopped
    networks:
      - app-network

  db:
    image: postgres:16-alpine
    environment:
      POSTGRES_USER: postgres
      POSTGRES_PASSWORD: password
      POSTGRES_DB: app
    volumes:
      - postgres_data:/var/lib/postgresql/data
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U postgres"]
      interval: 5s
      timeout: 5s
      retries: 5
    networks:
      - app-network

  redis:
    image: redis:7-alpine
    command: redis-server --appendonly yes
    volumes:
      - redis_data:/data
    networks:
      - app-network

volumes:
  postgres_data:
  redis_data:

networks:
  app-network:
    driver: bridge
```

## Security Hardening

```dockerfile
# .dockerignore
node_modules
.git
.env*
*.md
Dockerfile*
docker-compose*
.dockerignore
coverage
.nyc_output
```

```dockerfile
# Security-focused Dockerfile additions
FROM node:20-alpine AS runner

# Install security updates
RUN apk update && apk upgrade && \
    apk add --no-cache dumb-init && \
    rm -rf /var/cache/apk/*

# Prevent privilege escalation
RUN chmod u-s /usr/bin/* && \
    chmod g-s /usr/bin/*

# Use dumb-init for proper signal handling
ENTRYPOINT ["/usr/bin/dumb-init", "--"]
CMD ["node", "server.js"]
```

## Build Optimization

```bash
# Build with BuildKit for better caching
DOCKER_BUILDKIT=1 docker build \
  --cache-from myapp:latest \
  --build-arg BUILDKIT_INLINE_CACHE=1 \
  -t myapp:latest .

# Multi-platform builds
docker buildx build \
  --platform linux/amd64,linux/arm64 \
  -t myapp:latest \
  --push .
```

## Health Checks

```typescript
// src/api/health/route.ts
export async function GET() {
  const checks = {
    database: await checkDatabase(),
    redis: await checkRedis(),
    memory: process.memoryUsage(),
  };
  
  const healthy = checks.database && checks.redis;
  
  return Response.json(
    { status: healthy ? "healthy" : "unhealthy", checks },
    { status: healthy ? 200 : 503 }
  );
}
```

## Best Practices

- Use multi-stage builds to minimize image size
- Run containers as non-root users
- Implement proper health checks
- Use .dockerignore to exclude unnecessary files
- Pin base image versions for reproducibility
- Scan images for vulnerabilities with Trivy

Google Antigravity IDE provides Docker configuration templates and automatically detects security issues in your containerization setup.