Dockerfile Best Practices Checker

A well-crafted Dockerfile ensures that your containers are efficient, secure, and maintainable. Here are some best practices to follow when writing Dockerfiles:

Use Multi-stage Builds

Multi-stage builds allow you to use multiple FROM statements in your Dockerfile. This is useful for creating smaller production images by separating build-time dependencies from runtime dependencies.

FROM node:18 AS build
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
RUN npm run build

FROM node:18-alpine
WORKDIR /app
COPY --from=build /app/dist ./dist
CMD ["node", "dist/index.js"]

Minimize Layer Count and Size

• Group related commands in a single RUN instruction to reduce layers
• Clean up package manager caches in the same RUN instruction
• Use .dockerignore to exclude unnecessary files
• Choose smaller base images (e.g., alpine variants)

Security Best Practices

• Avoid running containers as root by using the USER instruction
• Set proper file permissions
• Never store secrets in the Dockerfile (use environment variables or secrets management)
• Scan images for vulnerabilities
• Use specific version tags instead of 'latest'

Additional Recommendations

• Use COPY instead of ADD for simple file copying
• Set WORKDIR instead of using RUN cd
• Use ENTRYPOINT with CMD for better container execution
• Include HEALTHCHECK instructions to monitor container health
• Sort multi-line arguments alphanumerically to avoid duplication