claudekit/.claude/skills/devops/docker/SKILL.md

Docker

Description

Docker containerization including Dockerfiles, compose, and best practices.

When to Use

• Containerizing applications
• Local development environments
• CI/CD pipelines

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Core Patterns

Multi-stage Dockerfile (Node.js)

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

# Production stage
FROM node:20-alpine
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/node_modules ./node_modules
EXPOSE 3000
CMD ["node", "dist/index.js"]

Python Dockerfile

FROM python:3.12-slim

WORKDIR /app

# Install dependencies first (caching)
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt

COPY . .

EXPOSE 8000
CMD ["uvicorn", "main:app", "--host", "0.0.0.0"]

Docker Compose

version: '3.8'

services:
  app:
    build: .
    ports:
      - "3000:3000"
    environment:
      - DATABASE_URL=postgresql://user:pass@db:5432/app
    depends_on:
      - db

  db:
    image: postgres:16-alpine
    environment:
      POSTGRES_USER: user
      POSTGRES_PASSWORD: pass
      POSTGRES_DB: app
    volumes:
      - postgres_data:/var/lib/postgresql/data

volumes:
  postgres_data:

Best Practices

1. Use multi-stage builds
2. Order commands for cache efficiency
3. Use .dockerignore
4. Run as non-root user
5. Use specific image tags

Common Pitfalls

• Large images: Use slim/alpine bases
• Cache busting: Order COPY commands properly
• Root user: Add USER instruction