10. Configuration, Environment & Secrets

.env Handling

FastAPI applications commonly rely on environment variables to externalize configuration. .env files provide a convenient way to define these variables during local development without embedding them in source code. This approach keeps configuration flexible while maintaining a clean separation from application logic.

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Settings Management with Pydantic

Pydantic provides a structured and type-safe way to manage application settings. Configuration values are defined as typed fields, validated at startup, and made available throughout the application. This prevents misconfiguration and surfaces errors early in the application lifecycle.

from pydantic import BaseSettings

class Settings(BaseSettings):
    app_name: str
    debug: bool = False
    database_url: str

    class Config:
        env_file = ".env"

settings = Settings()

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Separating Development and Production Behavior

FastAPI applications often behave differently across environments such as development, staging, and production. Environment-driven configuration enables features like debugging, logging levels, and dependency selection to vary without code changes. This separation reduces deployment risk and improves operational control.

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Avoiding Hard-Coded Credentials

Hard-coding credentials directly in source code introduces significant security and maintenance risks. FastAPI encourages loading secrets from environment variables or secure secret managers. This practice minimizes accidental exposure and supports safe rotation of sensitive values.