Docker & Containerization Skill

Roadmap Alignment: roadmap.sh/docker Reference: Docker Documentation

Core Standards (Effective Software Developer)

When writing or reviewing Dockerfiles and docker-compose.yml configurations, ensure they adhere to modern containerization best practices.

Base Images: Always use official, minimal base images (e.g., alpine, slim, or distroless) to reduce attack surface and download size. Pin specific versions (e.g., node:18-alpine instead of node:latest).
Multi-Stage Builds: Use multi-stage builds to separate build dependencies from runtime execution. Never ship source code, compilers, or test dependencies in a production image.
Layer Caching: Order commands from least likely to change to most likely to change. Copy dependency files (like package.json or Gemfile) and install dependencies before copying the rest of the source code.
Non-Root User: Never run containers as the root user in production. Always create a dedicated user and switch to it using the USER instruction.
Environment Variables: Use ENV to set defaults, but prefer passing secrets at runtime. Avoid hardcoding credentials in the Dockerfile.
Graceful Shutdown: Handle SIGTERM properly. Use CMD ["executable", "param1"] (exec form) rather than CMD command param1 (shell form) so the process receives signals correctly.