Using SignalR with Azure Table Storage - What architecture?

Question

I have a smart grid system where multiple hardware devices are sending raw sensor data to an Azure Queue. Each device sends a single data packet once every minute. Multiple Work

Answer 1

The first part of the solution I needed was to deploy a SignalR hub that the clients could connect to, to receive any notifications sent. I couldn't use the basic SignalR solution as the MVC5 web app is hosted on a Web Role that will likely have more than one instance - the problem was how to keep all these instances synced so that whatever instance a client was connected to they'd still receive the notifications. SignalR scaleout with Azure Service Bus proved to be the answer to that part of the problem. Details of how to set this up can be found at: http://www.asp.net/signalr/overview/signalr-20/performance-and-scaling/scaleout-with-windows-azure-service-bus - it was VERY easy to setup.

The second part of the problem was how to generate the notifications originating from the Worker Roles (my queue data processors). First I needed to be able to host OWIN in my worker roles - the instructions provided at http://www.asp.net/aspnet/overview/owin-and-katana/host-owin-in-an-azure-worker-role were more than sufficient. Once this was done I created an empty Hub instance with the same name as the one deployed on my Web Roles (it was empty because I didn't expect to have an clients connected to it directly), and changed the Startup class to:

public class Startup
{
    public void Configuration(IAppBuilder app)
    {
        String connectionString = "[Service Bus Connection String]";
        GlobalHost.DependencyResolver.UseServiceBus(connectionString, "[App Name]");
        app.MapSignalR();
    }
}

With this in place if I want to send a notification out to the clients, from the Worker Roles, I do something like:

var context = GlobalHost.ConnectionManager.GetHubContext<MyHub>();
context.Clients.All.clientMethod("[Message]");

What really happens is that a copy of the message gets pushed to the backplane (Service Bus) and is picked up by the Web Roles and pushed out to the connected clients. In reality I will check who is online (in the Web Role Hub instance I override the OnConnected method to save the user's connection id in their profile which is stored in Table Storage), and only create notifications that are associated with those users to reduce SignalR traffic.