AzureFunctions.DisabledWhen

Conditionally disable Azure Functions based on configuration values using attributes.

Installation

Simple setup

dotnet add package AzureFunctions.DisabledWhen

See sample/SampleFunctionApp for a working example.

Source generated setup

dotnet add package AzureFunctions.DisabledWhen
dotnet add package AzureFunctions.DisabledWhen.SourceGenerator

Add this to your .csproj to enable interceptors:

<PropertyGroup>
  <InterceptorsPreviewNamespaces>$(InterceptorsPreviewNamespaces);AzureFunctions.DisabledWhen</InterceptorsPreviewNamespaces>
</PropertyGroup>

See sample/SampleFunctionApp.SourceGenerated for a working example.

Note: The source generator only discovers functions in the same assembly where UseDisabledWhen() is called. If your functions are spread across multiple assemblies, use the reflection-based package instead.

Usage

1. Register the metadata provider

In your Program.cs, call UseDisabledWhen() on the builder after ConfigureFunctionsWebApplication():

using AzureFunctions.DisabledWhen;
using Microsoft.Azure.Functions.Worker.Builder;
using Microsoft.Extensions.Hosting;

var builder = FunctionsApplication.CreateBuilder(args);

builder.ConfigureFunctionsWebApplication();
builder.UseDisabledWhen();

var host = builder.Build();
host.Run();

The legacy IHostBuilder pattern is also supported:

var host = new HostBuilder()
    .ConfigureFunctionsWebApplication()
    .UseDisabledWhen()
    .Build();

host.Run();

Important: UseDisabledWhen() must be called after ConfigureFunctionsWebApplication() (or ConfigureFunctionsWorkerDefaults()) to ensure the default function metadata provider is registered first.

2. Apply attributes to functions

using AzureFunctions.DisabledWhen;

public class MyFunctions
{
    [Function("ScheduledCleanup")]
    [DisabledWhenLocal]
    public static void ScheduledCleanup(
        [TimerTrigger("0 */5 * * * *", RunOnStartup = true)] TimerInfo timer)
    {
    }

    [Function("ProcessOrderQueue")]
    [DisabledWhenNullOrEmpty("ServiceBusConnection")]
    public static void ProcessOrderQueue(
        [ServiceBusTrigger("orders", Connection = "ServiceBusConnection")] string message)
    {
    }

    [Function("GdprDataExport")]
    [DisabledWhen("EnvironmentOptions:RegionAbbreviation", "US", StringComparison.OrdinalIgnoreCase)]
    [DisabledWhen("EnvironmentOptions:RegionAbbreviation", "CA", StringComparison.OrdinalIgnoreCase)]
    [DisabledWhen("EnvironmentOptions:RegionAbbreviation", "AU", StringComparison.OrdinalIgnoreCase)]
    public static IActionResult GdprDataExport(
        [HttpTrigger(AuthorizationLevel.Function, "get", Route = "gdpr/export/{userId}")] HttpRequest req,
        string userId)
    {
    }
}

Attributes

DisabledWhenAttribute

Disables a function when a configuration key matches a specific value.

[DisabledWhen("ConfigKey", "ConfigValue")]
[DisabledWhen("ConfigKey", "ConfigValue", StringComparison.OrdinalIgnoreCase)]

DisabledWhenLocalAttribute

Disables a function when AZURE_FUNCTIONS_ENVIRONMENT equals Development.

[DisabledWhenLocal]

Read more about AZURE_FUNCTIONS_ENVIRONMENT.

DisabledWhenNullOrEmptyAttribute

Disables a function when a configuration key is missing, null, or empty.

[DisabledWhenNullOrEmpty("RequiredConfigKey")]

How It Works

The library provides a custom IFunctionMetadataProvider that evaluates attribute conditions at startup and excludes disabled functions from registration. The approach is inspired from this github issue.

When using both packages, the SourceGenerator intercepts calls to UseDisabledWhen() and replaces the reflection-based implementation with a compile-time generated version that is AOT-compatible.

Since filtering happens at startup:

• Configuration changes require a restart to take effect
• Disabled functions don't appear in the Azure Portal
• Disabled functions are logged as warnings

License

MIT