dockerfile-generator

# Dockerfile Generator ## Overview This skill provides a comprehensive workflow for generating production-ready Dockerfiles with security, optimization, and best practices built-in. Generates multi-stage builds, security-hardened configurations, and optimized layer structures with automatic validation and iterative error fixing. **Key Features:** - Multi-stage builds for optimal image size (50-85% reduction) - Security hardening (non-root users, minimal base images, no secrets) - Layer caching optimization for faster builds - Language-specific templates (Node.js, Python, Go, Java) - Automatic .dockerignore generation - Integration with `dockerfile-validator` for validation - Iterative validation and error fixing (minimum 1 iteration if errors found) - Local references plus docs lookup fallback chain for framework-specific patterns ## When to Use This Skill Invoke this skill when: - Creating new Dockerfiles from scratch - Containerizing applications (Node.js, Python, Go, Java, or other languages) - Implementing multi-stage builds for size optimization - Converting existing Dockerfiles to best practices - Generating production-ready container configurations - Optimizing Docker builds for security and performance - The user asks to "create", "generate", "build", or "write" a Dockerfile - Implementing containerization for microservices - Setting up CI/CD pipeline container builds ### Trigger Phrases Use this skill immediately when the request contains phrasing like: - "Generate a production Dockerfile for my app" - "Create a multi-stage Dockerfile for <language/framework>" - "Containerize this service with security best practices" - "Optimize this Dockerfile for size and build speed" - "Write Dockerfile and .dockerignore for deployment" ## Do NOT Use This Skill For - Validating existing Dockerfiles (use `dockerfile-validator` instead) - Building or running containers (use docker build/run commands) - Debugging running containers (use docker logs, docker exec) - Managing Docker images or registries ## Deterministic Execution Model Run these stages in order, and do not skip a stage unless the skip reason is reported in the final output. 1. Gather requirements (language, runtime version, entrypoint, exposed port, package manager, health endpoint). 2. Load references (local reference files first; external docs only when local references are insufficient). 3. Generate Dockerfile and `.dockerignore`. 4. Validate with `dockerfile-validator` or fallback local tools. 5. Iterate fixes until stop condition is met. 6. Publish final artifacts plus validation/audit report. Stop conditions for stage 5: - Stop when there are zero validation errors and no unapproved warnings. - Stop after 3 iterations maximum, then emit an intentional-deviation report for unresolved findings. ## Reference Path Map Consult these files directly by path as needed: - `references/security_best_practices.md` for non-root users, secret handling, base image hardening, vulnerability scanning. - `references/optimization_patterns.md` for multi-stage strategy, cache optimization, layer reduction, BuildKit cache mounts. - `references/language_specific_guides.md` for language/framework runtime and package-manager patterns. - `references/multistage_builds.md` for advanced stage-splitting and artifact-copy patterns. ## Dockerfile Generation Workflow Follow this workflow when generating Dockerfiles. Adapt based on user needs: ### Stage 1: Gather Requirements **Objective:** Understand what needs to be containerized and gather all necessary information. **Information to Collect:** 1. **Application Details:** - Programming language and version (Node.js 18/20, Python 3.11/3.12, Go 1.21+, Java 17/21, etc.) - Application type (web server, API, CLI tool, batch job, etc.) - Framework (Express, FastAPI, Spring Boot, etc.) - Entry point (main file, command to run) 2. **Dependencies:** - Package manager (npm/yarn/pnpm, pip/poetry, go mod, maven/gradle) - System dependencies (build tools, libraries, etc.) - Build-time vs runtime dependencies 3. **Application Configuration:** - Port(s) to expose - Environment variables needed - Configuration files - Health check endpoint (for web services) - Volume mounts (if any) 4. **Build Requirements:** - Build commands - Test commands (optional) - Compilation needs (for compiled languages) - Static asset generation 5. **Production Requirements:** - Expected image size constraints - Security requirements - Scaling needs - Resource constraints (CPU, memory) **Use AskUserQuestion if information is missing or unclear.** **Example Questions:** ``` - What programming language and version is your application using? - What is the main entry point to run your application? - Does your application expose any ports? If so, which ones? - Do you need any system dependencies beyond the base language runtime? - Does your application need a health check endpoint? ``` ### Stage 2: Framework/Library Documentation Lookup (if needed) **Objective:** Research framework-specific containerization patterns and best practices. **When to Perform This Stage:** - User mentions a specific framework (Next.js, Django, FastAPI, Spring Boot, etc.) - Application has complex build requirements - Need guidance on framework-specific optimization **Research Process (strict fallback chain):** 1. **Read local references first (required):** - `references/security_best_practices.md` - `references/optimization_patterns.md` - `references/language_specific_guides.md` 2. **Use Context7 docs lookup when local references are insufficient (preferred external source):** ``` Use mcp__context7__resolve-library-id with the framework name Then use mcp__context7__query-docs with query: "docker deployment production build" ``` 3. **Use web search only if Context7 is unavailable or missing needed details:** ``` "<framework>" "<version>" dockerfile production deployment best practices ``` 4. **If external lookup is unavailable (offline/tooling limits):** - Continue with local references and language templates in this file. - State assumptions explicitly in the output. - Mark the lookup limitation in the final report. 5. **Extract only actionable data:** - Recommended base image + version policy - Build optimization techniques - Required runtime environment variables - Production vs development differences - Security requirements specific to the framework ### Stage 3: Generate Dockerfile **Objective:** Create a production-ready, multi-stage Dockerfile following best practices. **Core Principles:** 1. **Multi-Stage Builds (REQUIRED for compiled languages, RECOMMENDED for all):** - Separate build stage from runtime stage - Keep build tools out of final image - Copy only necessary artifacts - Results in 50-85% smaller images 2. **Security Hardening (REQUIRED):** - Use specific version tags (NEVER use :latest) - Run as non-root user (create dedicated user) - Use minimal base images (alpine, distroless) - No hardcoded secrets - Scan base images for vulnerabilities 3. **Layer Optimization (REQUIRED):** - Order instructions from least to most frequently changing - Copy dependency files before application code - Combine related RUN commands with && - Clean up package manager caches in same layer - Leverage build cache effectively 4. **Production Readiness (REQUIRED):** - Add HEALTHCHECK for services - Use exec form for ENTRYPOINT/CMD - Set WORKDIR to absolute paths - Document exposed ports with EXPOSE **Language-Specific Templates:** #### Node.js Multi-Stage Dockerfile > **Build-stage dependency rule:** If the application has a build step (TypeScript, > Vite, Webpack, etc.), install **all** dependencies in the builder stage (omit > `--only=production`) and prune dev deps after the build. Using > `--only=production` before a build step will cause `npm run build` to fail > because dev tools are not installed. ```dockerfile # syntax=docker/dockerfile:1 # Build stage — installs all deps so build tools (tsc, vite, etc.) are available, # then prunes dev deps so the production stage only ships what is needed at runtime. FROM node:20-alpine AS builder WORKDIR /app # Copy dependency files for caching COPY package*.json ./ # Install ALL dependencies (including devDependencies required by the build step) RUN npm ci && \ npm cache clean --force # Copy application code COPY . . # Build application and prune dev dependencies RUN npm run build && \ npm prune --production # Production stage FROM node:20-alpine AS production WORKDIR /app # Set production environment ENV NODE_ENV=production # Create non-root user RUN addgroup -g 1001 -S nodejs && \ adduser -S nodejs -u 1001 # Copy pruned node_modules and built application from builder COPY --from=builder --chown=nodejs:nodejs /app/node_modules ./node_modules COPY --from=builder --chown=nodejs:nodejs /app . # Switch to non-root user USER nodejs # Expose port EXPOSE 3000 # Health check HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \ CMD node -e "require('http').get('http://localhost:3000/health', (r) => {process.exit(r.statusCode === 200 ? 0 : 1)})" # Start application CMD ["node", "index.js"] ``` > **Simple app (no build step):** If there is no compilation or bundling, install > only production deps in the builder stage and copy source from the host context: > ```dockerfile > RUN npm ci --only=production && npm cache clean --force > ... > COPY --from=builder --chown=nodejs:nodejs /app/node_modules ./node_modules > COPY --chown=nodejs:nodejs . . > ``` #### Python Multi-Stage Dockerfile ```dockerfile # syntax=docker/dockerfile:1 # Build stage FROM python:3.12-slim AS builder WORKDIR /app # Install build dependencies # hadolint ignore=DL3008 RUN apt-get update && apt-get install -y --no-install-recommends \ gcc \ && rm -rf /var/lib/apt/lists/* # Copy dependency files COPY requirements.txt . # Install Python dependencies RUN pip install --no-cache-dir --user -r requirements.txt # Production stage FROM python:3.12-slim AS production WORKDIR /app # Create non-root user RUN useradd -m -u 1001 appuser # Copy dependencies from builder COPY --from=builder /root/.local /home/appuser/.local # Copy application code COPY --chown=appuser:appuser . . # Update PATH and set Python production env vars # PYTHONUNBUFFERED=1 ensures stdout/stderr are flushed immediately (essential for container logs) # PYTHONDONTWRITEBYTECODE=1 prevents writing .pyc files to disk ENV PATH=/home/appuser/.local/bin:$PATH \ PYTHONUNBUFFERED=1 \ PYTHONDONTWRITEBYTECODE=1 # Switch to non-root user USER appuser # Expose port EXPOSE 8000 # Health check (adjust endpoint as needed) HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \ CMD python -c "import urllib.request; urllib.request.urlopen('http://localhost:8000/health').read()" || exit 1 # Start application CMD ["python", "app.py"] ``` #### Go Multi-Stage Dockerfile ```dockerfile # syntax=docker/dockerfile:1 # Build stage FROM golang:1.21-alpine AS builder WORKDIR /app # Copy go mod files COPY go.mod go.sum ./ RUN go mod download # Copy source code COPY . . # Build the application RUN CGO_ENABLED=0 GOOS=linux go build -a -ldflags="-s -w" -o main . # Production stage (using distroless for minimal image) # gcr.io/distroless/static-debian12 IS a specific tag; hadolint DL3006 is a # false positive for non-Docker-Hub registries. # hadolint ignore=DL3006 FROM gcr.io/distroless/static-debian12 AS production WORKDIR / # Copy binary from builder COPY --from=builder /app/main /main # Expose port EXPOSE 8080 # HEALTHCHECK is not supported in distroless images (no shell available) # Switch to non-root user (distroless runs as nonroot by default) USER nonroot:nonroot # Start application ENTRYPOINT ["/main"] ``` #### Java Multi-Stage Dockerfile ```dockerfile # syntax=docker/dockerfile:1 # Build stage FROM eclipse-temurin:21-jdk-jammy AS builder WORKDIR /app # Copy Maven wrapper and pom.xml COPY mvnw pom.xml ./ COPY .mvn .mvn # Download dependencies (cached layer) RUN ./mvnw dependency:go-offline # Copy source code COPY src ./src # Build application RUN ./mvnw clean package -DskipTests && \ mv target/*.jar target/app.jar # Production stage (using JRE instead of JDK) FROM eclipse-temurin:21-jre-jammy AS production WORKDIR /app # Install healthcheck dependency and create non-root user # hadolint ignore=DL3008 RUN apt-get update && apt-get install -y --no-install-recommends curl && \ rm -rf /var/lib/apt/lists/* && \ useradd -m -u 1001 appuser # Copy JAR from builder COPY --from=builder --chown=appuser:appuser /app/target/app.jar ./app.jar # Switch to non-root user USER appuser # Expose port EXPOSE 8080 # Health check HEALTHCHECK --interval=30s --timeout=3s --start-period=40s --retries=3 \ CMD curl -f http://localhost:8080/actuator/health || exit 1 # Start application ENTRYPOINT ["java", "-jar", "app.jar"] ``` **Selection Logic:** - Node.js: Use for JavaScript/TypeScript applications - Python: Use for Python applications (web, API, scripts) - Go: Use for Go applications (excellent for minimal images) - Java: Use for Spring Boot, Quarkus, or other Java frameworks - Generic: Create custom Dockerfile for other languages **Always Include:** 1. Syntax directive: `# syntax=docker/dockerfile:1` 2. Multi-stage build (build + production stages) 3. Non-root user creation and usage 4. HEALTHCHECK for services (if applicable) 5. Proper WORKDIR settings 6. EXPOSE for documented ports 7. Clean package manager caches 8. exec form for CMD/ENTRYPOINT ### Stage 4: Generate .dockerignore **Objective:** Create comprehensive .dockerignore to reduce build context and prevent secret leaks. **Always create .dockerignore with generated Dockerfile.** **Standard .dockerignore Template:** ``` # Git .git .gitignore .gitattributes # CI/CD .github .gitlab-ci.yml .travis.yml .circleci # Documentation README.md CHANGELOG.md CONTRIBUTING.md LICENSE *.md docs/ # Docker Dockerfile* docker-compose*.yml .dockerignore # Environment .env .env.* *.local # Logs logs/ *.log npm-debug.log* yarn-debug.log* yarn-error.log* # Dependencies (language-specific - add as needed) node_modules/ __pycache__/ *.pyc *.pyo *.pyd .Python venv/ .venv/ target/ *.class # IDE .vscode/ .idea/ *.swp *.swo *~ .DS_Store # Testing coverage/ .coverage *.cover .pytest_cache/ .tox/ test-results/ # Build artifacts dist/ build/ *.egg-info/ ``` **Customize based on language:** - Node.js: Add `node_modules/`, `npm-debug.log`, `yarn-error.log` - Python: Add `__pycache__/`, `*.pyc`, `.venv/`, `.pytest_cache/` - Go: Add `vendor/`, `*.exe`, `*.test` - Java: Add `target/`, `*.class`, `*.jar` (except final artifact) ### Stage 5: Validate with `dockerfile-validator`