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What is the Options pattern, and what is the difference between IOptions, IOptionsSnapshot and IOptionsMonitor?

ASP.NET Core Configuration Intermediate 2–3 Yrs3–5 Yrs Conceptual 1 min read

Quick Answer

The Options pattern binds a configuration section to a strongly typed class and injects it. IOptions<T> — singleton, value read once, no reload. IOptionsSnapshot<T> — scoped, re-read per request, picks up file changes. IOptionsMonitor<T> — singleton with change notifications, works in singletons and background services.

The Options pattern is how I get strongly typed settings — I bind a config section like Smtp to an SmtpOptions class and inject it instead of pulling strings out of IConfiguration. The three interfaces differ in reload behaviour and lifetime. IOptions is a singleton, read once — fine for settings that don't change while the app runs, which is most of them. IOptionsSnapshot is scoped and re-reads per request, so it picks up changes to the config file, but you can't use it in a singleton. IOptionsMonitor is a singleton that supports change notifications, so it's what I use in a background service. I also add ValidateOnStart so bad config fails fast.

IOptions<T>IOptionsSnapshot<T>IOptionsMonitor<T>
LifetimeSingletonScopedSingleton
Reloads on config changeNoYes (per request)Yes (via OnChange / CurrentValue)
Usable in a singletonYesNoYes
Named optionsNoYesYes
  • Register: services.Configure<SmtpOptions>(config.GetSection("Smtp")).
  • Add validation: .ValidateDataAnnotations().ValidateOnStart() so a bad config fails at startup, not at first use.
  • Use IOptions for settings that never change at run time (the common case), IOptionsSnapshot in request-scoped code that must see live edits, IOptionsMonitor in singletons / hosted services.
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