Azure Worker Role - HttpListener - Error 503. The service is unavailable

Question

I m developing a worker role on Azure. It is using OWIN to start a web app on the port 8080 in the goal of working with SignalR. This works perfectly.

Now, I need to create an HTTP listener to listen to incoming POST requests on port 27045.

I did the following to create and run the HttpListener object:

var endpoint = RoleEnvironment.CurrentRoleInstance.InstanceEndpoints["listenerendpoint"];
var port = endpoint.IPEndpoint.Port.ToString();   

var listener = new HttpListener();

listener.Prefixes.Add("http://*:" + port + "/");
listener.Start();

Now, in the worker role's Run method:

IAsyncResult listenerResult = null;

while (true)
{
    if (listenerResult == null || listenerResult.IsCompleted)
            listenerResult = listener.BeginGetContext(new AsyncCallback(ListenerCallback), listener);

    Thread.Sleep(1000);
}

And here is the ListenerCallback method:

public static void ListenerCallback(IAsyncResult result)
{
    var listener = (HttpListener)result.AsyncState;
    var context = listener.EndGetContext(result);

    var request = context.Request;

    var reader = new StreamReader(request.InputStream);

    var payload = reader.ReadToEnd();
}

I set up the endpoint for my listener in the ServiceDefinition.csdef file as following:

<WorkerRole name="myworkerrole" vmsize="Standard_D1_v2">
    <ConfigurationSettings>
      <Setting name="Microsoft.WindowsAzure.Plugins.Diagnostics.ConnectionString" />
    </ConfigurationSettings>
    <Endpoints>
      <InputEndpoint name="mainendpoint" protocol="http" port="8080" localPort="8080" />
      <InputEndpoint name="listenerendpoint" protocol="http" port="27045" localPort="27045" />
    </Endpoints>
    <Runtime executionContext="elevated" />
</WorkerRole>

Finally, here is the AJAX test client I developed:

$.ajax({
  method: "POST",
  url: "http://myworkerrolename.cloudapp.net:27045/",
  data: "testdata",
  crossDomain: true,
  dataType: "jsonp"
}).done(function(msg) {
    console.log('done');
    console.log(msg);
}).fail(function(msg) {
    console.log('fail');
    console.log(msg);
});

When I run the worker role locally using Azure Compute Emulator, everything works perfectly, I m able to send a post request to the endpoint. But when I deploy in the cloud, I m always getting the same AJAX error:

readyState: 4
status: 404
statusText: error

And if I open my browser and try to reach the url provided in the AJAX client configuration, it gives me the following error: HTTP Error 503. The service is unavailable.

I've set up try/catch at HttpListener creation but it never goes on the catch block. Everything seems to run well but the error is still here.

Thanks

stephgou stephgou · Accepted Answer · 2015-12-30T19:16:12

I would suggest to add the complete prefix to your listener

So you may keep :

 listener.Prefixes.Add("http://*:" + port + "/");

But add also :

 listener.Prefixes.Add("http://yourapp.cloudapp.net:" + port + "/");

Hope this helps Best regards Stéphane

Azure Worker Role - HttpListener - Error 503. The service is unavailable

2 Answers