Intro: Building Apps That Don’t Suck in Production Let’s be honest—plenty of apps “work on my machine” but self-destruct the moment they meet the real world. Configs hardcoded, logs missing, environments confused, and deployments that feel like an escape room puzzle. If you want your service to thrive in production (and not become an ops horror story), you need a design philosophy that enforces clean separation, modularity, and resilience. That's where the 12 Factor App methodology comes in. In this post, we’re going to break down each of the 12 Factor using a Python/FastAPI related stack—and walk through how to get them right. 🧱 The Twelve Factor — Python Style Let’s take each principle, one by one. Think of it as a devops dojo, with Python as your katana. Codebase: One codebase tracked in revision control, many deploys 12 Factor App: Single source of truth, version-controlled, no Franken-repos. 📌 In Python: One Git repo per service. Don't share code across projects via copy-paste. Use internal packages or shared libraries (published to private PyPI or via Git submodules). ✅ Best Practice: /fastapi-12factor-app ├── app/ │ ├── api/ │ ├── core/ │ ├── models/ │ └── main.py ├── tests/ ├── Dockerfile ├── pyproject.toml ├── README.md └── .env Dependencies: Explicitly declare and isolate dependencies 12 Factor App: No implicit magic. Use virtualenvs and lock your deps. 📌 In Python: Use pyproject.toml and a tool like Poetry or pip-tools. ✅ Example pyproject.toml: [tool.poetry.dependencies] python = "^3.12" fastapi = "^0.110.0" uvicorn = "^0.29.0" sqlalchemy = "^2.0" pydantic = "^2.6" python-dotenv = "^1.0" 🔒 Lock it…