AspNetCore.HealthCheck in Azure function always returns 200 even when unhealthy

We have an Azure Function using .Net Core 7 that we've added a HealthCheck to. The healthcheck fires, if the status is set to unhealthy, we return a an instance of ServiceUnavailableObjectResult. The HTTP status code always returns 200 regardless of what we return.

From Program.cs

services.AddHealthChecks()
    .AddUrlGroup(
        uri: new Uri($"{baseAddress}/health"),
        name: "Mgmt")
    .AddAzureBlobStorage(
        connectionString: context.Configuration.GetValue<string>(RecipientUploadOptions.BlobConnectionStringName),
        containerName: context.Configuration.GetValue<string>(RecipientUploadOptions.IncomingContainerName),
        name: "IncomingBlobContainer")
    .AddAzureBlobStorage(
        connectionString: context.Configuration.GetValue<string>(RecipientUploadOptions.BlobConnectionStringName),
        containerName: context.Configuration.GetValue<string>(RecipientUploadOptions.ErrorContainerName),
        name: "ErrorBlobContainer")
    .AddAzureBlobStorage(
        connectionString: context.Configuration.GetValue<string>(RecipientUploadOptions.BlobConnectionStringName),
        containerName: context.Configuration.GetValue<string>(RecipientUploadOptions.ArchiveContainerName),
        name: "ArchiveBlobContainer");

From HealthCheckFunction.cs

[Function("health")]
public async Task<IActionResult> Health([HttpTrigger(AuthorizationLevel.Anonymous, "get", "post")] HttpRequestData z)
{
    var status = await _healthCheckService.CheckHealthAsync();
    if (status.Status == HealthStatus.Healthy)
    {
        return new OkObjectResult(Enum.GetName(typeof(HealthStatus), status.Status));
    }

    return new ServiceUnavailableObjectResult(Enum.GetName(typeof(HealthStatus), status.Status));
}

Expected:

• The HTTP status code returned is 503 - Service Unavailable along with the payload.

Actual:

• The HTTP status code returned os 200 - OK along with the payload
• The same code used for HealthChecks in web API projects return 503 as expected

Any suggestions would be greatly appreaciated

There are two ways you can develop HTTP functions when using .NET Isloted Worker.

Built-in HTTP Model

For this you need to return the HttpResponseData type as follows

[Function(nameof(Health))]
public async Task<HttpResponseData> Health([HttpTrigger(AuthorizationLevel.Function, "get", "post")] HttpRequestData req)
{
    var response = req.CreateResponse();

    var status = await _healthCheckService.CheckHealthAsync();

    await response.WriteAsJsonAsync(
        Enum.GetName(typeof(HealthStatus), status.Status),
        status.Status == HealthStatus.Healthy ? HttpStatusCode.OK : HttpStatusCode.ServiceUnavailable
    );

    return response;
}

ASP.NET Core integration (preview)

There are a few pre-requisites to get this model to work which are documented in the doc linked above. Here are the same for reference.

1. Install the Microsoft.Azure.Functions.Worker.Extensions.Http.AspNetCore NuGet package, version 1.0.0-preview2 or later (Note that you must check the include prerelease checkbox in Visual Studio)

   Also, make sure Microsoft.Azure.Functions.Worker.Sdk is version 1.11.0 or later and Microsoft.Azure.Functions.Worker is version 1.16.0 or later.

2. Replace ConfigureFunctionsWorkerDefaults with ConfigureFunctionsWebApplication in Program.cs

3. Use HttpRequest and IActionResult types from ASP.NET

4. Add the AzureWebJobsFeatureFlags app setting with value EnableHttpProxying

Here is implementation based on Pramod's answer here.

[Function(nameof(Health))]
public async Task<HttpResponseData> Health([HttpTrigger(AuthorizationLevel.Function, "get", "post")] HttpRequestData req)
{
    //HACK (Work around)
    //Due to a behavior in the Azure Function framework for health checks
    //will always return a 200 regardless of state and ignore the
    //IActionResult. The solution--for now--is to get closer to the metal
    //and write our own response body. ASP.NET Core integration (for Azure
    //Functions) is still in preview (and not solving the problem for us
    //right this moment but may hold the key for doing this better in the
    //future.

    var response = req.CreateResponse();

    var status = await _healthCheckService.CheckHealthAsync();

    var httpStatus = (status.Status == HealthStatus.Healthy
        ? HttpStatusCode.OK
        : HttpStatusCode.ServiceUnavailable);

    var statusResult = new
    {
        Value = Enum.GetName(typeof(HealthStatus), status.Status),
        Formatters = new string[] { },
        // Entries = status.Entries,
        // ^^^^ This would be nice but doesn't directly serialize and will
        // throw a NotSupportedException. That may be useful to explore
        // since it gives details about what is unhealthy
        ContentType = "application/json",
        StatusCode = httpStatus
    };

    await response.WriteAsJsonAsync(statusResult, httpStatus);

    return response;
}