Docker Composer Skill

Overview

This skill helps you create efficient Docker configurations for development and production. Covers Dockerfiles, Docker Compose, multi-stage builds, networking, volumes, and container orchestration best practices.

Docker Philosophy

Container Principles

One process per container: Keep containers focused
Immutable infrastructure: Don't modify running containers
Stateless containers: Store state in volumes or external services
Minimal images: Smaller = faster + more secure

Best Practices

DO: Use multi-stage builds for production
DO: Pin specific versions for dependencies
DO: Use .dockerignore to exclude unnecessary files
DO: Run as non-root user
DON'T: Store secrets in images or Dockerfiles
DON'T: Use latest tag in production
DON'T: Install unnecessary packages

Dockerfile Patterns

Node.js Production Dockerfile

Dockerfile

============================================

Stage 1: Dependencies

============================================

FROM node:20-alpine AS deps WORKDIR /app

Install dependencies only when needed

COPY package.json package-lock.json ./ RUN npm ci --only=production

============================================

Stage 2: Builder

============================================

FROM node:20-alpine AS builder WORKDIR /app

COPY package.json package-lock.json ./ RUN npm ci

COPY . .

Build application

ENV NEXT_TELEMETRY_DISABLED 1 RUN npm run build

============================================

Stage 3: Runner (Production)

============================================

FROM node:20-alpine AS runner WORKDIR /app

ENV NODE_ENV production ENV NEXT_TELEMETRY_DISABLED 1

Create non-root user

RUN addgroup --system --gid 1001 nodejs RUN adduser --system --uid 1001 nextjs

Copy built assets

COPY --from=builder /app/public ./public COPY --from=builder --chown=nextjs:nodejs /app/.next/standalone ./ COPY --from=builder --chown=nextjs:nodejs /app/.next/static ./.next/static

USER nextjs

EXPOSE 3000

ENV PORT 3000 ENV HOSTNAME "0.0.0.0"

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

Python Production Dockerfile

Dockerfile

============================================

Stage 1: Builder

============================================

FROM python:3.11-slim AS builder

WORKDIR /app

Install build dependencies

RUN apt-get update && apt-get install -y --no-install-recommends
build-essential
&& rm -rf /var/lib/apt/lists/*

Create virtual environment

RUN python -m venv /opt/venv ENV PATH="/opt/venv/bin:$PATH"

Install dependencies

COPY requirements.txt . RUN pip install --no-cache-dir -r requirements.txt

============================================

Stage 2: Runner

============================================

FROM python:3.11-slim AS runner

WORKDIR /app

Create non-root user

RUN groupadd --gid 1000 appgroup
&& useradd --uid 1000 --gid appgroup --shell /bin/bash appuser

Copy virtual environment

COPY --from=builder /opt/venv /opt/venv ENV PATH="/opt/venv/bin:$PATH"

Copy application

COPY --chown=appuser:appgroup . .

USER appuser

EXPOSE 8000

CMD ["gunicorn", "--bind", "0.0.0.0:8000", "app:app"]

Development Dockerfile

Dockerfile.dev

FROM node:20-alpine

WORKDIR /app

Install development dependencies

RUN apk add --no-cache git

Copy package files first (for caching)

COPY package.json package-lock.json ./

Install all dependencies (including devDependencies)

RUN npm install

Don't copy files - mount as volume for hot reload

COPY . .

EXPOSE 3000

CMD ["npm", "run", "dev"]

Docker Compose Configurations

Full-Stack Development

docker-compose.yml

version: '3.8'

services:

===================

Application

===================

app: build: context: . dockerfile: Dockerfile.dev ports: - "3000:3000" volumes: - .:/app - /app/node_modules # Exclude node_modules environment: - NODE_ENV=development - DATABASE_URL=postgresql://postgres:postgres@db:5432/myapp - REDIS_URL=redis://redis:6379 depends_on: db: condition: service_healthy redis: condition: service_started networks: - app-network

===================

Database

===================

db: image: postgres:15-alpine ports: - "5432:5432" environment: POSTGRES_USER: postgres POSTGRES_PASSWORD: postgres POSTGRES_DB: myapp volumes: - postgres_data:/var/lib/postgresql/data - ./init.sql:/docker-entrypoint-initdb.d/init.sql healthcheck: test: ["CMD-SHELL", "pg_isready -U postgres"] interval: 5s timeout: 5s retries: 5 networks: - app-network

===================

Redis Cache

===================

redis: image: redis:7-alpine ports: - "6379:6379" volumes: - redis_data:/data command: redis-server --appendonly yes networks: - app-network

===================

Admin Tools

===================

adminer: image: adminer ports: - "8080:8080" depends_on: - db networks: - app-network

volumes: postgres_data: redis_data:

networks: app-network: driver: bridge

Production Configuration

docker-compose.prod.yml

version: '3.8'

services: app: image: myapp:${VERSION:-latest} build: context: . dockerfile: Dockerfile ports: - "3000:3000" environment: - NODE_ENV=production env_file: - .env.production deploy: replicas: 3 resources: limits: cpus: '0.5' memory: 512M reservations: cpus: '0.25' memory: 256M restart_policy: condition: on-failure delay: 5s max_attempts: 3 healthcheck: test: ["CMD", "curl", "-f", "http://localhost:3000/api/health"] interval: 30s timeout: 10s retries: 3 start_period: 40s logging: driver: "json-file" options: max-size: "10m" max-file: "3" networks: - app-network depends_on: - db - redis

db: image: postgres:15-alpine environment: POSTGRES_USER: ${DB_USER} POSTGRES_PASSWORD_FILE: /run/secrets/db_password POSTGRES_DB: ${DB_NAME} secrets: - db_password volumes: - postgres_data:/var/lib/postgresql/data deploy: resources: limits: cpus: '1' memory: 1G networks: - app-network

redis: image: redis:7-alpine command: redis-server --requirepass ${REDIS_PASSWORD} volumes: - redis_data:/data networks: - app-network

nginx: image: nginx:alpine ports: - "80:80" - "443:443" volumes: - ./nginx.conf:/etc/nginx/nginx.conf:ro - ./certs:/etc/nginx/certs:ro depends_on: - app networks: - app-network

secrets: db_password: file: ./secrets/db_password.txt

volumes: postgres_data: redis_data:

networks: app-network: driver: overlay

Development Override Pattern

docker-compose.override.yml (auto-loaded with docker-compose.yml)

version: '3.8'

services: app: build: context: . dockerfile: Dockerfile.dev volumes: - .:/app - /app/node_modules environment: - DEBUG=true - LOG_LEVEL=debug command: npm run dev

db: ports: - "5432:5432" # Expose for local tools

redis: ports: - "6379:6379" # Expose for local tools

Advanced Patterns

Multi-Service Monorepo

docker-compose.yml

version: '3.8'

services:

Frontend

web: build: context: . dockerfile: apps/web/Dockerfile ports: - "3000:3000" environment: - API_URL=http://api:4000 depends_on: - api networks: - frontend - backend

Backend API

api: build: context: . dockerfile: apps/api/Dockerfile ports: - "4000:4000" environment: - DATABASE_URL=postgresql://postgres:postgres@db:5432/myapp - REDIS_URL=redis://redis:6379 depends_on: - db - redis networks: - backend

Background Workers

worker: build: context: . dockerfile: apps/worker/Dockerfile environment: - DATABASE_URL=postgresql://postgres:postgres@db:5432/myapp - REDIS_URL=redis://redis:6379 depends_on: - db - redis deploy: replicas: 2 networks: - backend

Shared services

db: image: postgres:15-alpine volumes: - postgres_data:/var/lib/postgresql/data networks: - backend

redis: image: redis:7-alpine volumes: - redis_data:/data networks: - backend

networks: frontend: backend:

volumes: postgres_data: redis_data:

Local Services Stack

docker-compose.services.yml

Run local versions of external services for development

version: '3.8'

services:

Local S3-compatible storage

minio: image: minio/minio ports: - "9000:9000" - "9001:9001" # Console volumes: - minio_data:/data environment: MINIO_ROOT_USER: minioadmin MINIO_ROOT_PASSWORD: minioadmin command: server /data --console-address ":9001"

Local email testing

mailhog: image: mailhog/mailhog ports: - "1025:1025" # SMTP - "8025:8025" # Web UI

Local Stripe webhooks

stripe-cli: image: stripe/stripe-cli command: listen --api-key ${STRIPE_SECRET_KEY} --forward-to http://app:3000/api/webhooks/stripe depends_on: - app

Elasticsearch

elasticsearch: image: elasticsearch:8.11.0 ports: - "9200:9200" environment: - discovery.type=single-node - xpack.security.enabled=false - "ES_JAVA_OPTS=-Xms512m -Xmx512m" volumes: - elasticsearch_data:/usr/share/elasticsearch/data

Kibana (Elasticsearch UI)

kibana: image: kibana:8.11.0 ports: - "5601:5601" environment: ELASTICSEARCH_HOSTS: http://elasticsearch:9200 depends_on: - elasticsearch

volumes: minio_data: elasticsearch_data:

Testing Configuration

docker-compose.test.yml

version: '3.8'

services: app: build: context: . dockerfile: Dockerfile.test environment: - NODE_ENV=test - DATABASE_URL=postgresql://postgres:postgres@db:5432/myapp_test depends_on: db: condition: service_healthy command: npm run test:ci

db: image: postgres:15-alpine environment: POSTGRES_USER: postgres POSTGRES_PASSWORD: postgres POSTGRES_DB: myapp_test tmpfs: - /var/lib/postgresql/data # Use tmpfs for speed healthcheck: test: ["CMD-SHELL", "pg_isready -U postgres"] interval: 2s timeout: 5s retries: 5

E2E testing

playwright: image: mcr.microsoft.com/playwright:v1.40.0-focal volumes: - .:/app - /app/node_modules working_dir: /app environment: - CI=true - BASE_URL=http://app:3000 depends_on: - app command: npx playwright test

.dockerignore

Dependencies

node_modules npm-debug.log yarn-error.log

Build output

.next dist build out

Development

.git .gitignore *.md !README.md

IDE

.vscode .idea *.swp *.swo

Environment

.env .env.* !.env.example

Tests

coverage *.test.js *.spec.js tests e2e playwright-report

Docker

Dockerfile* docker-compose* .docker

Misc

.DS_Store *.log tmp

Docker Commands Reference

Development Workflow

Start development environment

docker-compose up -d

View logs

docker-compose logs -f app

Rebuild after package changes

docker-compose up -d --build

Run one-off commands

docker-compose exec app npm run migrate docker-compose exec app npm run seed

Stop everything

docker-compose down

Stop and remove volumes (reset database)

docker-compose down -v

Production Workflow

Build production image

docker build -t myapp:1.0.0 .

Run with production config

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

Scale services

docker-compose up -d --scale app=3

Rolling update

docker-compose pull app docker-compose up -d --no-deps app

Debugging

Shell into running container

docker-compose exec app sh

Inspect container

docker inspect <container_id>

View resource usage

docker stats

Clean up unused resources

docker system prune -a

View networks

docker network ls docker network inspect app-network

Health Checks

Application Health Check

// src/app/api/health/route.ts import { NextResponse } from 'next/server';

export async function GET() { const checks = { uptime: process.uptime(), timestamp: new Date().toISOString(), database: false, redis: false, };

try { // Check database await db.execute('SELECT 1'); checks.database = true; } catch (e) { console.error('Database health check failed:', e); }

try { // Check Redis await redis.ping(); checks.redis = true; } catch (e) { console.error('Redis health check failed:', e); }

const isHealthy = checks.database && checks.redis;

return NextResponse.json(checks, { status: isHealthy ? 200 : 503 }); }

Docker Health Check

HEALTHCHECK --interval=30s --timeout=10s --start-period=5s --retries=3
CMD curl -f http://localhost:3000/api/health || exit 1

Checklist

Dockerfile

Multi-stage build for production
Non-root user
Minimal base image (alpine when possible)
Layer caching optimized (dependencies before code)
Health check defined
.dockerignore configured

Docker Compose

Services have health checks
Volumes for persistent data
Networks for service isolation
Resource limits defined
Restart policies configured
Environment variables externalized

Security

No secrets in Dockerfile or docker-compose
Images scanned for vulnerabilities
Minimal privileges (no root)
Network isolation between services

When to Use This Skill

Invoke this skill when:

Containerizing a new application
Setting up development environments with Docker
Creating multi-service architectures
Optimizing Docker builds
Debugging container issues
Setting up CI/CD pipelines with Docker
Migrating from docker-compose to Kubernetes

docker-composer

Safety Notice

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Dockerfile

============================================

Stage 1: Dependencies

============================================

Install dependencies only when needed

============================================

Stage 2: Builder

============================================

Build application

============================================

Stage 3: Runner (Production)

============================================

Create non-root user

Copy built assets

Dockerfile

============================================

Stage 1: Builder

============================================

Install build dependencies

Create virtual environment

Install dependencies

============================================

Stage 2: Runner

============================================

Create non-root user

Copy virtual environment

Copy application

Dockerfile.dev

Install development dependencies

Copy package files first (for caching)

Install all dependencies (including devDependencies)

Don't copy files - mount as volume for hot reload

COPY . .

docker-compose.yml

===================

Application

===================

===================

Database

===================

===================

Redis Cache

===================

===================

Admin Tools

===================

docker-compose.prod.yml

docker-compose.override.yml (auto-loaded with docker-compose.yml)

docker-compose.yml

Frontend

Backend API

Background Workers

Shared services

docker-compose.services.yml

Run local versions of external services for development

Local S3-compatible storage

Local email testing

Local Stripe webhooks

Elasticsearch

Kibana (Elasticsearch UI)

docker-compose.test.yml

E2E testing

.dockerignore

Dependencies

Build output

Development

IDE

Environment

Tests

Docker

Misc

Start development environment

View logs

Rebuild after package changes

Run one-off commands

Stop everything

Stop and remove volumes (reset database)