ln-731-docker-generator

Paths: File paths (shared/, references/, ../ln-*) are relative to skills repo root. If not found at CWD, locate this SKILL.md directory and go up one level for repo root.

ln-731-docker-generator

Type: L3 Worker Category: 7XX Project Bootstrap Parent: ln-730-devops-setup

Generates production-ready Docker configuration for containerized development.

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Purpose & Scope

Creates Docker infrastructure for local development and production:

• Does: Generate Dockerfiles, docker-compose, .dockerignore, nginx config
• Does NOT: Build images, start containers, manage deployments

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Inputs

Input	Source	Description
Stack Type	ln-730 coordinator	frontend, backend-dotnet, backend-python
Versions	Auto-detected	Node.js, .NET, Python versions
Project Name	Directory name	Used for container naming
Ports	Defaults or detected	Frontend: 3000, Backend: 5000/8000, DB: 5432

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Outputs

File	Purpose	Template
Dockerfile.frontend	Frontend build & serve	dockerfile_frontend.template
Dockerfile.backend	Backend build & run	dockerfile_backend_dotnet.template or dockerfile_backend_python.template
docker-compose.yml	Service orchestration	docker_compose.template
.dockerignore	Build context exclusions	dockerignore.template
nginx.conf	Frontend proxy config	nginx.template

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Workflow

Phase 1: Input Validation

Validate received configuration from coordinator:

• Check stack type is supported (frontend, backend-dotnet, backend-python)
• Verify versions are valid (Node 18+, .NET 8+, Python 3.10+)
• Confirm project directory exists

Output: Validated configuration or error

Phase 2: Template Selection

Select appropriate templates based on stack:

Stack	Templates Used
Frontend only	dockerfile_frontend, nginx, dockerignore
Backend .NET	dockerfile_backend_dotnet, docker_compose, dockerignore
Backend Python	dockerfile_backend_python, docker_compose, dockerignore
Full stack .NET	All of the above (dotnet variant)
Full stack Python	All of the above (python variant)

Phase 3: Variable Substitution

Replace template variables with detected values:

Variable	Source	Example
{{NODE_VERSION}}	package.json engines or default	22
{{DOTNET_VERSION}}	*.csproj TargetFramework	9.0
{{PYTHON_VERSION}}	pyproject.toml or default	3.12
{{PROJECT_NAME}}	Directory name	my-app
{{DLL_NAME}}	*.csproj AssemblyName	MyApp.Api.dll
{{FRONTEND_PORT}}	Default or detected	3000
{{BACKEND_PORT}}	Stack-dependent	5000 (.NET), 8000 (Python)
{{BACKEND_HOST}}	Service name	backend
{{CMD}}	Framework-dependent	["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000"] (FastAPI) or ["gunicorn", "--bind", "0.0.0.0:8000", "{{PROJECT_NAME}}.wsgi:application"] (Django)

Phase 4: File Generation

Generate files from templates:

1. Check if file already exists (warn before overwrite)
2. Apply variable substitution
3. Write file to appropriate location
4. Validate syntax where possible

File Locations:

• Dockerfile.frontend -> src/frontend/Dockerfile
• Dockerfile.backend -> project root
• docker-compose.yml -> project root
• .dockerignore -> project root
• nginx.conf -> src/frontend/nginx.conf

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Supported Stacks

Frontend: React/Vite + Nginx

Requirements:

• package.json with build script
• Vite or CRA configuration

Generated:

• Multi-stage Dockerfile (builder + nginx)
• Nginx config with SPA routing and API proxy

Backend: .NET 8/9

Requirements:

• *.sln file in root
• *.csproj with TargetFramework

Generated:

• Multi-stage Dockerfile (SDK build + ASP.NET runtime)
• Health check endpoint configuration

Backend: Python (FastAPI/Django)

Requirements:

• requirements.txt or pyproject.toml

Generated:

• Multi-stage Dockerfile (builder + slim runtime)
• uvicorn (FastAPI) or gunicorn (Django) entrypoint

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Security & Performance Best Practices

All generated files follow these guidelines:

Practice	Implementation
Non-root user	Create and use appuser (UID 1001)
Minimal images	Alpine/slim variants
Multi-stage builds	Exclude build tools from runtime
No secrets	Use environment variables, not hardcoded
Health checks	Built-in HEALTHCHECK instructions (wget/curl)
Specific versions	Pin base image versions (e.g., nginx:1.27-alpine)
Non-interactive mode	ARG DEBIAN_FRONTEND=noninteractive
Layer caching	Copy dependency files first, source code last
BuildKit cache	Use --mount=type=cache for pip
Python optimization	PYTHONDONTWRITEBYTECODE=1, PYTHONUNBUFFERED=1

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Quality Criteria

Generated files must meet:

• [ ] docker-compose config validates without errors
• [ ] All base images use specific versions (not latest)
• [ ] Non-root user configured in all Dockerfiles
• [ ] Health checks present for all services
• [ ] .dockerignore excludes all sensitive files
• [ ] No hardcoded secrets or passwords

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Critical Notes

1. Version Detection: Use detected versions from coordinator, not hardcoded defaults.
2. Idempotent: Check file existence before writing. Warn if overwriting.
3. Template-based: All generation uses templates from references/. Do NOT hardcode file contents.
4. Security First: Every generated file must follow security best practices.

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Reference Files

File	Purpose
dockerfile_frontend.template	React/Vite multi-stage Dockerfile
dockerfile_backend_dotnet.template	.NET multi-stage Dockerfile
dockerfile_backend_python.template	Python multi-stage Dockerfile
docker_compose.template	docker-compose.yml template
dockerignore.template	.dockerignore template
nginx.template	Nginx configuration

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Version: 1.2.0 Last Updated: 2026-01-21