The Tool Desk
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What the .NET Options pattern does
Microsoft describes the Options pattern as using classes to provide strongly typed access to groups of related settings. Instead of scattering configuration lookups throughout an application, define a class for a coherent settings group, bind configuration to it, register it with dependency injection, and inject the relevant options interface into consumers. See Microsoft’s .NET Options pattern guide.
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Keep each options class focused on the settings a scenario needs. That keeps configuration concerns encapsulated and separate from unrelated application behavior. The configuration section name does not have to equal the class name: registration connects the section to the CLR type. Using nameof(MyOptions) is convenient when the names happen to match, not a requirement.
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Bind a configuration section and register it
A common registration binds a section to an options class in the service-registration code:
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builder.Services.Configure<TransientFaultHandlingOptions>(
builder.Configuration.GetSection("TransientFaultHandling"));The class might contain properties matching the section’s keys:
public sealed class TransientFaultHandlingOptions
{
public bool Enabled { get; set; }
public int AutoRetryDelay { get; set; }
}After registration, inject the interface that fits the consumer. For example, a service that uses the ordinary startup configuration can accept IOptions<TransientFaultHandlingOptions>:
public sealed class RetryService
{
private readonly TransientFaultHandlingOptions _settings;
public RetryService(IOptions<TransientFaultHandlingOptions> options)
{
_settings = options.Value;
}
}The same registered options type can be consumed through IOptionsSnapshot<T> or IOptionsMonitor<T> where their scope and update behavior are needed.
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| Interface | Lifetime and consistency | Updates and named options | Use it when |
|---|---|---|---|
IOptions<T> |
Singleton; injectable into any service lifetime. Value is not refreshed from updated configuration after startup. | Does not support named options or reload. | The consumer needs a simple default configuration and does not need changes after startup. |
IOptionsSnapshot<T> |
Scoped; unsuitable for injection into a singleton. Options are computed on access and cached for the scope. | Supports named options. A scope sees its cached snapshot. | A scoped or transient consumer needs a consistent view for a request or other scope. |
IOptionsMonitor<T> |
Singleton; injectable into any service lifetime. Provides current values. | Supports named options, change notifications, and cache invalidation; reload depends on the configuration source and environment. | A singleton or other consumer must retrieve current values or react to configuration changes. |
These lifetime and capability differences are documented in Microsoft’s Options pattern guide. A practical rule is to use IOptions<T> unless the application has a concrete need for a scope-specific snapshot, named configurations, or updates after startup. Choose the monitor for a long-lived consumer that must observe changes; choose the snapshot when the desired boundary is a request or scope.
What reload actually depends on
IOptionsMonitor<T> can expose updated values and notify listeners, but it cannot make a configuration source report changes if that source or deployment environment does not support change tracking. Microsoft lists file-based providers such as JSON, INI, XML, Key per File, and User Secrets among sources that support reload scenarios. Some Docker and network file systems may not reliably raise file-change notifications.
For environments where file notifications are unreliable, Microsoft documents polling through the DOTNET_USE_POLLING_FILE_WATCHER setting, with a four-second polling interval. This is an environment-specific workaround, not a guarantee that every provider or filesystem can reload. Consult the Options documentation for the supported-source and watcher details.
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Use named options for multiple configurations
Named options let one options type represent multiple configurations, such as settings for distinct named clients. Configure each instance through the named-options APIs, then retrieve the intended instance by name using IOptionsSnapshot<T> or IOptionsMonitor<T>, both of which support names. IOptions<T> does not. The exact configuration mechanism depends on how the application registers its named instances; Microsoft documents the named options APIs in the Options pattern guide.
Validate settings at startup or when options are created
Invalid settings are easier to diagnose when rejected near application startup rather than after a code path first uses them. Options validation can use data annotations, a custom validator, or class-level IValidatableObject validation. Add ValidateOnStart to have the host validate the options during startup:
builder.Services.AddOptions<TransientFaultHandlingOptions>()
.Bind(builder.Configuration.GetSection("TransientFaultHandling"))
.ValidateDataAnnotations()
.ValidateOnStart();For rules that annotations cannot express, implement an options validator or use IValidatableObject. Microsoft’s Options guide describes the validation approaches and startup validation.
Understand synchronous validation during access and reload
In the documented .NET 10 options paths, ordinary value access, snapshot creation, and reloads observed through IOptionsMonitor<T> are synchronous; they do not invoke asynchronous validators. The .NET 10 IOptionsMonitor<TOptions> API reference states that the default monitor recreates and validates options synchronously after change notifications and does not call ValidateAsync. An asynchronous validator can therefore cause reload validation to fail and prevent change listeners from being called. Do not treat monitor reload as an asynchronous validation workflow or as a last-known-good fallback.
What happens behind the options interfaces
Most applications can begin with section binding and the options builder. For custom configuration pipelines, two underlying services explain how options are produced and reused:
IOptionsFactory<TOptions>creates options instances by applying registered configuration and post-configuration.IOptionsMonitorCache<TOptions>stores monitor instances and supports removing or clearing cached values so they can be recomputed.
Microsoft documents these extension points in the Options pattern guide and the .NET 10 monitor API reference. They matter when building custom options behavior, but are not prerequisites for ordinary dependency-injection registration.
Quick Recap
A quick decision checklist
- Use
IOptions<T>when one default value set is sufficient and configuration is not expected to change for the consumer. - Use
IOptionsSnapshot<T>when a scoped consumer needs a scope-specific cached view or named options. - Use
IOptionsMonitor<T>when a singleton or other long-lived component needs current values, named options, or change notifications. - For any reload-based design, confirm that the configuration provider and runtime filesystem actually report changes.
- Use
ValidateOnStartwhen invalid configuration should fail during host startup, and account for synchronous validation in monitor reload paths.
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