12-Factor

Environment variables are the 12-factor way to configure applications. But “just use env vars” glosses over real complexity. Here’s how to do it well. The Basics Done Right Type Coercion Environment variables are always strings. Handle conversion explicitly: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 import os def get_env_bool(key: str, default: bool = False) -> bool: value = os.getenv(key, "").lower() if value in ("true", "1", "yes", "on"): return True if value in ("false", "0", "no", "off"): return False return default def get_env_int(key: str, default: int = 0) -> int: try: return int(os.getenv(key, default)) except ValueError: return default # Usage DEBUG = get_env_bool("DEBUG", False) PORT = get_env_int("PORT", 8080) WORKERS = get_env_int("WORKERS", 4) Required vs Optional Fail fast on missing required config: ...

The third factor of the 12-Factor App methodology states: “Store config in the environment.” Simple advice that’s surprisingly easy to get wrong. The Core Principle Configuration that varies between environments (dev, staging, production) should come from environment variables, not code. This includes: Database connection strings API keys and secrets Feature flags Service URLs Port numbers Log levels What stays in code: application logic, default behaviors, anything that doesn’t change between deploys. ...