Microsoft.Extensions.Options.OptionsValidationException – Configuration options validation failed

The Microsoft.Extensions.Options.OptionsValidationException with the message “Configuration options validation failed” occurs in .NET applications when the validation of configuration options fails. This typically happens when using the IOptions<T>, IOptionsSnapshot<T>, or IOptionsMonitor<T> pattern in ASP.NET Core to bind and validate configuration settings.

Here’s a detailed explanation of the issue and how to resolve it:

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Common Causes

1. Missing Required Configuration Values

• A required configuration value is missing from the configuration source (e.g., appsettings.json, environment variables).

1. Invalid Configuration Values

• A configuration value does not meet the validation rules (e.g., a string is too short, a number is out of range).

1. Validation Rules Not Met

• The validation rules defined for the options class are not satisfied.

1. Configuration Binding Issues

• The configuration section is not correctly bound to the options class.

1. Incorrect Configuration Structure

• The structure of the configuration file does not match the expected structure for the options class.

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Solutions

1. Check Configuration Values

• Ensure all required configuration values are present in the configuration source (e.g., appsettings.json). Example appsettings.json:

   {
       "MySettings": {
           "ApiKey": "your-api-key",
           "Timeout": 30
       }
   }

2. Define Validation Rules

• Use data annotations or custom validation logic to define validation rules for the options class. Example with Data Annotations:

   public class MySettings
   {
       [Required]
       public string ApiKey { get; set; }

       [Range(1, 60)]
       public int Timeout { get; set; }
   }

3. Register and Validate Options

• Register the options class and enable validation in the ConfigureServices method. Example in Program.cs (ASP.NET Core 6+):

   var builder = WebApplication.CreateBuilder(args);

   // Bind and validate configuration
   builder.Services.AddOptions<MySettings>()
       .Bind(builder.Configuration.GetSection("MySettings"))
       .ValidateDataAnnotations()
       .Validate(settings => settings.Timeout > 0, "Timeout must be greater than 0.");

   var app = builder.Build();

Example in Startup.cs (ASP.NET Core 5 or earlier):

   public void ConfigureServices(IServiceCollection services)
   {
       // Bind and validate configuration
       services.AddOptions<MySettings>()
           .Bind(Configuration.GetSection("MySettings"))
           .ValidateDataAnnotations()
           .Validate(settings => settings.Timeout > 0, "Timeout must be greater than 0.");
   }

4. Handle Validation Errors Gracefully

• Catch the OptionsValidationException and log or handle it appropriately. Example:

   try
   {
       var mySettings = app.Services.GetRequiredService<IOptions<MySettings>>().Value;
   }
   catch (OptionsValidationException ex)
   {
       Console.WriteLine($"Configuration validation failed: {ex.Message}");
       // Log or handle the exception
   }

5. Check Configuration Binding

• Ensure the configuration section name matches the section being bound. Example:

   // Correct binding
   builder.Services.AddOptions<MySettings>()
       .Bind(builder.Configuration.GetSection("MySettings"));

6. Use Custom Validators

• For complex validation logic, implement a custom validator by implementing the IValidateOptions<T> interface. Example:

   public class MySettingsValidator : IValidateOptions<MySettings>
   {
       public ValidateOptionsResult Validate(string name, MySettings options)
       {
           if (string.IsNullOrEmpty(options.ApiKey))
           {
               return ValidateOptionsResult.Fail("ApiKey is required.");
           }
           return ValidateOptionsResult.Success;
       }
   }

   // Register the custom validator
   builder.Services.AddSingleton<IValidateOptions<MySettings>, MySettingsValidator>();

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Debugging Tips

• Use logging to inspect the configuration values being loaded.
• Verify the structure of the configuration file matches the options class.
• Check the exception details for specific validation errors.

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Best Practices

• Always validate configuration options to ensure the application starts with valid settings.
• Use meaningful error messages in validation rules to make debugging easier.
• Avoid hardcoding configuration values; always use the configuration system.
• Regularly review and update configuration files to ensure they meet the application’s requirements.

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Example of a Complete Setup

Options Class

public class MySettings
{
    [Required]
    public string ApiKey { get; set; }

    [Range(1, 60)]
    public int Timeout { get; set; }
}

Configuration File (appsettings.json)

{
    "MySettings": {
        "ApiKey": "your-api-key",
        "Timeout": 30
    }
}

Service Registration and Validation

var builder = WebApplication.CreateBuilder(args);

// Bind and validate configuration
builder.Services.AddOptions<MySettings>()
    .Bind(builder.Configuration.GetSection("MySettings"))
    .ValidateDataAnnotations()
    .Validate(settings => settings.Timeout > 0, "Timeout must be greater than 0.");

var app = builder.Build();

Using the Options

app.MapGet("/", (IOptions<MySettings> mySettings) =>
{
    return Results.Ok(mySettings.Value);
});

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