Docker Workflow

Overview

Docker containerization streamlines development, testing, and deployment by packaging applications with their dependencies into portable, reproducible containers. This skill guides you through professional Docker workflows from development to production.

Core Capabilities

• Multi-stage builds: Separate build and runtime dependencies for optimal image size
• Docker Compose orchestration: Manage multi-container applications with networking and dependencies
• Image optimization: Reduce image size by 50-90% through best practices
• Development workflows: Hot-reload, volume mounting, and environment-specific configs
• Debugging tools: Container inspection, health checks, and troubleshooting utilities
• Production readiness: Security hardening, health checks, and deployment strategies

When to Use This Skill

Activate when:

• Containerizing a new application
• Setting up development environments with Docker
• Creating production-ready Docker images
• Orchestrating multi-container applications
• Debugging container issues
• Optimizing Docker builds and images

Workflow Phases

Phase 1: Initial Setup

Create .dockerignore

Exclude unnecessary files from build context:

node_modules/
__pycache__/
*.pyc
.git/
.env
*.log
dist/
build/
coverage/

See examples/.dockerignore for comprehensive template.

Key principles:

• Exclude build artifacts and dependencies
• Exclude sensitive files (.env, credentials)
• Exclude version control (.git)
• Smaller context = faster builds

Analyze Application Requirements

Determine:

• Runtime (Node.js, Python, Go, Java)
• Dependencies and package managers
• Build vs. runtime requirements
• Port exposure and volume needs

Phase 2: Multi-Stage Dockerfile

Choose Strategy

Multi-stage builds reduce final image size by 50-90%:

# Stage 1: Build
FROM node:18-alpine AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production
COPY . .
RUN npm run build

# Stage 2: Production
FROM node:18-alpine
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/node_modules ./node_modules
EXPOSE 3000
CMD ["node", "dist/index.js"]

See examples/Dockerfile.multi-stage for templates for Node.js, Python, Go, Java, and Rust.

Optimize Layer Caching

Order matters - place changing content last:

# ✅ GOOD: Dependencies cached separately
COPY package.json package-lock.json ./
RUN npm ci
COPY . .

# ❌ BAD: Any file change invalidates cache
COPY . .
RUN npm ci

Apply Security Best Practices

# Use specific versions
FROM node:18.17.1-alpine

# Run as non-root user
RUN addgroup -g 1001 -S nodejs && adduser -S nodejs -u 1001
USER nodejs

# Copy with ownership
COPY --chown=nodejs:nodejs . .

Security checklist:

• Pin base image versions
• Use minimal base images (alpine, slim)
• Run as non-root user
• Scan for vulnerabilities
• Minimize installed packages

Phase 3: Docker Compose Setup

Define Services

Create docker-compose.yml:

version: '3.8'

services:
  app:
    build:
      context: .
      dockerfile: Dockerfile
    ports:
      - "3000:3000"
    environment:
      - DATABASE_URL=postgresql://db:5432/myapp
    depends_on:
      db:
        condition: service_healthy
    volumes:
      - ./src:/app/src  # Development hot-reload
    networks:
      - app-network

  db:
    image: postgres:15-alpine
    environment:
      POSTGRES_DB: myapp
    volumes:
      - postgres-data:/var/lib/postgresql/data
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U user"]
      interval: 5s
    networks:
      - app-network

volumes:
  postgres-data:

networks:
  app-network:

See examples/docker-compose.yml for full-featured setup with monitoring, queues, and caching.

Environment Configuration

Use override files for different environments:

Development (docker-compose.override.yml):

services:
  app:
    build:
      target: development
    volumes:
      - ./src:/app/src
    environment:
      - NODE_ENV=development
    command: npm run dev

Production (docker-compose.prod.yml):

services:
  app:
    build:
      target: production
    restart: always
    environment:
      - NODE_ENV=production

Usage:

# Development (uses override automatically)
docker-compose up

# Production
docker-compose -f docker-compose.yml -f docker-compose.prod.yml up -d

Phase 4: Build and Run

Build Commands

# Basic build
docker build -t myapp:latest .

# Build specific stage
docker build --target production -t myapp:prod .

# Build with BuildKit (faster)
DOCKER_BUILDKIT=1 docker build -t myapp:latest .

Run Commands

# Single container
docker run -d -p 3000:3000 -e NODE_ENV=production myapp:latest

# Docker Compose
docker-compose up -d

# View logs
docker-compose logs -f app

# Execute in container
docker-compose exec app sh

# Stop and remove
docker-compose down -v

Phase 5: Debugging and Troubleshooting

Use Helper Script

The scripts/docker_helper.sh utility provides common debugging operations:

# Check container health
./scripts/docker_helper.sh health myapp

# Inspect details
./scripts/docker_helper.sh inspect myapp

# View logs
./scripts/docker_helper.sh logs myapp 200

# Open shell
./scripts/docker_helper.sh shell myapp

# Analyze image size
./scripts/docker_helper.sh size myapp:latest

# Cleanup resources
./scripts/docker_helper.sh cleanup

Common Issues

Container exits immediately:

docker logs myapp
docker run -it --entrypoint sh myapp:latest

Network connectivity:

docker network inspect myapp_default
docker exec myapp ping db

Volume permissions:

# Fix in Dockerfile
RUN chown -R nodejs:nodejs /app/data

Phase 6: Optimization

Reduce Image Size

Strategies:

1. Use smaller base images (alpine > slim > debian)
2. Multi-stage builds to exclude build tools
3. Combine RUN commands for fewer layers
4. Clean up in same layer
5. Use .dockerignore

Example:

# ✅ GOOD: Combined, cleaned up
RUN apt-get update && \
    apt-get install -y --no-install-recommends package1 && \
    apt-get clean && \
    rm -rf /var/lib/apt/lists/*

Build Performance

# Enable BuildKit
export DOCKER_BUILDKIT=1

# Use cache mounts
RUN --mount=type=cache,target=/root/.cache/pip \
    pip install -r requirements.txt

# Parallel builds
docker-compose build --parallel

Phase 7: Production Deployment

Production Dockerfile

FROM node:18-alpine AS production

# Security: non-root user
RUN addgroup -g 1001 -S nodejs && adduser -S nodejs -u 1001

WORKDIR /app
COPY --from=builder --chown=nodejs:nodejs /app/dist ./dist
USER nodejs

# Health check
HEALTHCHECK --interval=30s --timeout=3s \
  CMD node healthcheck.js

EXPOSE 3000
CMD ["node", "dist/index.js"]

Deployment Commands

# Tag for registry
docker tag myapp:latest registry.example.com/myapp:v1.0.0

# Push to registry
docker push registry.example.com/myapp:v1.0.0

# Deploy
docker-compose pull && docker-compose up -d

# Rolling update
docker-compose up -d --no-deps --build app

Common Patterns

Full-Stack Application

• Frontend + Backend + Database + Redis
• See examples/docker-compose.yml

Microservices

• API Gateway + Multiple Services + Message Queue
• Network isolation and service discovery

Development with Hot Reload

• Volume mounting for source code
• Override files for dev configuration

Best Practices Summary

Security

✅ Use specific image versions, not latest ✅ Run as non-root user ✅ Use secrets management for sensitive data ✅ Scan images for vulnerabilities ✅ Use minimal base images

Performance

✅ Use multi-stage builds ✅ Optimize layer caching ✅ Use .dockerignore ✅ Combine RUN commands ✅ Use BuildKit

Development

✅ Use d