Docker Expert Skill

This skill optimizes Dockerfiles for size, speed, and security.

Best Practices

1. •Multi-Stage Builds: Separate build tools from runtime artifacts.
   dockerfile

   FROM golang:1.21 as builder
   ...
   FROM alpine:latest
   COPY --from=builder /app/bin /bin
   

2. •Layer Caching: Order instructions from least changed to most changed. Copy go.mod/package.json before source code.
3. •Security:
   • •Do not run as root (USER nonroot).
   • •Use trusted base images (e.g., distroless).
   • •Scan for vulnerabilities (if trivy is installed).
4. •Optimization:
   • •Combine RUN commands to reduce layers: RUN apt-get update && apt-get install -y ... && rm -rf /var/lib/apt/lists/*

Usage

When asked to "fix Dockerfile" or "dockerize this":

• •Read existing Dockerfile.
• •Apply the above rules.
• •Check .dockerignore to ensure .git, node_modules, etc., are excluded.