microsoft-extensions-configuration

You validate configuration on startup by binding appsettings sections to strongly-typed POCO settings and registering validation using Data Annotations or IValidateOptions to enforce fail-fast behavior on invalid values.

IOptions provides static singleton configuration, IOptionsSnapshot reloads settings per request, and IOptionsMonitor supports dynamic reloading scenarios to help you choose the appropriate options lifetime for your appsettings-based app.

Basic Options binding maps configuration sections to strongly-typed settings classes so code can rely on typed properties rather than string keys, centralizing appsettings-based configuration management across .NET services.

IValidateOptions is used for complex validation rules requiring cross-field and external dependency checks. These DI-enabled validators run during startup, providing robust fail-fast behavior beyond simple Data Annotations.

Post-configuration applies tweaks before validation to normalize values or set defaults. This allows you to adjust bound configuration properties dynamically, ensuring normalized data passes subsequent startup validation checks.

Common anti-patterns include bypassing validation entirely and performing validation inside constructors. Always prefer startup validation to ensure fail-fast behavior and catch invalid appsettings configuration immediately.