Aspire.Hosting.Dcp.dcpctrl.ServiceReconciler[0]: could not start the proxy {"ServiceName": {"name":"core-api"}, "Reconciliation": 21, "error": "could not start the proxy for the service: listen tcp 127.0.0.1:9000: bind: address already in use"}

[tmarkovski]

Is there an existing issue for this?

• I have searched the existing issues
• There are older issue where this was a breaking bug, in my case it's not breaking

Describe the bug

This is an error reported to the console, but the Aspire host and the services run and operate correctly as intended. Here's my setup.

var coreService = builder.AddProject<Projects.Server>("core-api")
    .WithHttpEndpoint(env: "PORT", port: 9000)
    .WithExternalHttpEndpoints();

In the above, I'm instructing Aspire to set the PORT variable to whatever internal port it will assign, but expose the endpoint to the specific port.

In my service, I simply bind to the PORT env variable.

if (int.TryParse(Environment.GetEnvironmentVariable("PORT") ?? "8080", out var port) && port is < 1 or > 65535)
{
    throw new Exception("PORT must be a valid integer between 1 and 65535");
}
builder.WebHost.UseKestrel(options =>
{
    options.ListenAnyIP(port, listenOptions =>
    {
        listenOptions.Protocols = HttpProtocols.Http1AndHttp2;
    });
});

The above works fine, I get my service exposed to port 9000, internally running on targetPort.

However, the Aspire host console continues complaining about:

fail: Aspire.Hosting.Dcp.dcpctrl.ServiceReconciler[0]
      could not start the proxy {"ServiceName": {"name":"core-api"}, "Reconciliation": 21, "error": "could not start the proxy for the service: listen tcp 127.0.0.1:9000: bind: address already in use"}

Expected Behavior

The log error should not be there.

Steps To Reproduce

• Create new Aspire host
• Add .NET Core service
• Configure as shown in the bug description

Exceptions (if any)

No response

.NET Version info

net9, aspire sdk 9

Anything else?

No response