SYSLIB0066: IStartupValidator is obsolete

Starting in .NET 11, IStartupValidator is obsolete. When you reference or implement this interface, the compiler generates warning SYSLIB0066 with the message Implement IAsyncStartupValidator instead. The interface remains available and functional for compatibility.

Reason for obsoletion

Host startup has an asynchronous entry point through StartAsync. New custom startup validators should use IAsyncStartupValidator. Its asynchronous ValidateAsync contract means asynchronous implementations don't need to provide an unused synchronous Validate method. The two interfaces are independent.

Workaround

To migrate a custom startup validator, implement and register IAsyncStartupValidator instead. Use asynchronous operations in ValidateAsync when validation requires them, and forward the cancellation token. Register the implementation only under the startup-validation contract it provides; don't register it under both IStartupValidator and IAsyncStartupValidator.

Applications that only call OptionsBuilder<TOptions>.ValidateOnStart() and don't directly implement a startup-validator interface normally don't need to change their code.

Suppress a warning

If you must use the obsolete interface, you can suppress the warning in code or in your project file.

To suppress a single violation, add preprocessor directives to your source file to disable and then re-enable the warning.

#pragma warning disable SYSLIB0066

// Code that uses the obsolete interface.

#pragma warning restore SYSLIB0066

To suppress all SYSLIB0066 warnings in your project, add a <NoWarn> property to your project file.

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <NoWarn>$(NoWarn);SYSLIB0066</NoWarn>
  </PropertyGroup>
</Project>

For more information, see Suppress warnings.