Azure – Isolated Function App not responding to HTTP calls

I have previously used in-process function apps without any issue.

I start them with func host start, and then I can invoke any REST endpoints locally using cURL.

To keep up with later dotnet versions, I’ve decided to give the isolated runtime a try.

I’ve setup a very simple project that only exposes a single endpoint, as outlined in the documentation for the http trigger

public class RestEndpoints
{
    private readonly ILogger<RestEndpoints> _logger;

    public RestEndpoints(ILogger<RestEndpoints> logger)
    {
        _logger = logger;
    }

    [Function(nameof(Run))]
    public HttpResponseData Run([HttpTrigger(AuthorizationLevel.Anonymous, "get", Route = null)] HttpRequestData req,
        FunctionContext executionContext)
    {
        _logger.LogInformation("message logged");

        var response = req.CreateResponse(HttpStatusCode.OK);
        response.Headers.Add("Content-Type", "text/plain; charset=utf-8");
        response.WriteString("Welcome to .NET isolated worker !!");

        return response;
    }
}

In Program.cs I have the baseline setup. From what I’ve read I can’t see anything additional is needed for this scenario:

using Microsoft.Extensions.Hosting;

var host = new HostBuilder()
    .ConfigureFunctionsWorkerDefaults()
    .Build();

host.Run();

I start this application the same way as I did in-process with func host start. It starts alright and lists my endpoint as:

Run: [GET] http://localhost:7071/api/Run

However, when I try to invoke this using cURL, the call just hangs. I can see log output that the runtime was reached, but I cannot get a response from the endpoint:

[2023-08-22T09:48:28.362Z] Executing ‘Functions.Run’ (Reason=’This function was programmatically called via the host APIs.’, Id=98b63dcc-dce5-4b9d-bee8-dee1ea98a653)

In my csproj file I have the following dependencies:

<PackageReference Include="Microsoft.Azure.Functions.Worker" Version="1.8.0"/>
<PackageReference Include="Microsoft.Azure.Functions.Worker.Extensions.Http" Version="3.1.0" />
<PackageReference Include="Microsoft.Azure.Functions.Worker.Sdk" Version="1.7.0"/>
<PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="7.0.0" />

I am using Azure Function Core Tools 4.46.0.

What am I missing here?

Trying debug mode

As pointed out to me, I tried debug mode as well but I get the same result:

func host start --pause-on-error --dotnet-isolated-debug --enable-json-output

Azure Functions Core Tools
Core Tools Version:       4.0.5274 Commit hash: N/A  (64-bit)
Function Runtime Version: 4.23.0.20886

[2023-08-22T11:34:02.028Z] Found MyProject.csproj. Using for user secrets file configuration.
[2023-08-22T11:34:04.234Z] Azure Functions .NET Worker (PID: 70640) initialized in debug mode. Waiting for debugger to attach...

Functions:

    Run: [GET] http://localhost:7071/api/Run

For detailed output, run func with --verbose flag.
[2023-08-22T11:34:09.120Z] Host lock lease acquired by instance ID '000000000000000000000000C146DC40'.
[2023-08-22T11:34:10.565Z] Worker process started and initialized.
[2023-08-22T11:35:12.462Z] Executing 'Functions.Run' (Reason='This function was programmatically called via the host APIs.', Id=2a8207da-dc97-447e-b9de-60facda8481c)

The last line in the above output is from me using cURL to try and invoke the endpoint, then nothing else happens.