Null Reference Null Reference - 2 months ago 15
C# Question

HTTP 503 Service is unavailable when trying to browse signalr/hubs

I have a windows hosted SignalR hub created in VS2012:

public class Startup
{
public void Configuration(IAppBuilder app)
{
app.UseCors(CorsOptions.AllowAll);
app.MapSignalR();
}
}

public static class SignalR
{
public static void Start()
{
const string url = "http://*:8080";
WebApp.Start<Startup>(url);
}
}

public class Broadcaster : Hub
{

public void SendDownloadResult(bool result, string device, string description, string connectionId, string task)
{
var context = GlobalHost.ConnectionManager.GetHubContext<Broadcaster>();
context.Clients.Client(connectionId).sendDownloadResult(result, device, description, task);
}
}


I have deployed this windows service on 3 different PCs, it works fine on two PCs, but on the other, I get HTTP 503 Service is unavailable when I try to browse
http://localhost:8080/signalr/hubs


No exception thrown when the code is executed on all 3 PCs.

I have checked IIS's features in add/remove windows features, they're all the same.

What am I missing?

Answer

I was able to reproduce this locally with the following setup:

  1. Use NetSh.exe or similar tool to reserve http://localhost:8080/
  2. Call WebApp.Start<Startup>("http://*:8080")
  3. Browse to http://localhost:8080/

What happens is that Http.Sys accepts the incoming request, examines the host header, decides that there is a reservation for localhost:8080, but realizes that no application is listening to localhost:8080, only *:8080. Http.Sys then returns the 503.

Solutions:

  1. Try WebApp.Start<Startup>("http://+:8080")
  2. Remove the Http.Sys/NetSh registration
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