Using SignalR with Azure Table Storage - What architecture? - asp.net-mvc

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 Worker Roles process the data packets on the queue and push the data to Table Storage. I have a Web Role which holds the application for users to view their device data and a host of other alerts and messages relating to their smart energy system. At the moment the web application just uses ajax polling at one minute intervals to get the latest data updates and any other messages and alerts. Instead of using ajax 'pulling', I'd like to use SignalR instead and 'push' the updates from the cloud when they become available. I'm not sure on what the overall architecture might look like.
So far I have added a SignalR Hub to my Web Role, just to see if I could do that. And it works fine. However, how do I trigger updates from this Hub when there are changes in Table Storage? Should I host the Hub with the Worker Roles that process the raw data, and then make a cross-domain SignalR connection from the web app (client)? Can I even associate an endpoint with a Worker Role? If I have many Worker Roles wouldn't I only be able to connect to one of them, and therefore miss data updates from other Worker Roles?
Perhaps I should create a separate Web Role to host the SignalR hub, but then how do I communicate the changes from the Worker Roles that process the raw data to the hub? Maybe I need to include another Azure Queue that takes messages from the Worker Roles regarding data updates, alerts, and any other messaging, and that queue is processed by the SignalR server. However, would this approach be scalable? If I have multiple instances of the SignalR server processing the message queue(s), would they share the same end point and be aware of all the client connections across the instances? Or maybe the Worker Roles themselves connect as clients to the SignalR server and the messages forwarded from there to the clients.
Is SignalR even the right approach to take if data is being generated at a predictable rate of once every minute for each device. Maybe for updates of this regular data ajax 'pulling' is the best approach, and I should just be using SignalR for the infrequent alerts and messages, although, again, how do I communicate these events from the Worker Roles to the SignalR server?
What overall architecture would suit my needs here?
EDIT 06-09-2014 Half the problem solved
I came across http://www.asp.net/signalr/overview/signalr-20/performance-and-scaling/scaleout-with-windows-azure-service-bus which seems to be exactly what I am after. This deals with the problem of multiple Hub server (Web Role) instances. Now I just need a SignalR client library that can run on the Worker Roles so that they can notify the Hub that new data is available, and the Hub class can then be enhanced to route the new data to the appropriate connected web clients.
EDIT 06-10-2014 A workable solution found
I have added an answer to my question of "What architecture". I thought a quick summary of my setup might be useful. I have many remote devices associated with different users posting real-time data to Azure Queues. The data posted to these queues are parsed and saved to Table Storage, by a number of Worker Roles. Web Roles provide the MVC5 web application for the users (clients) to log on and review their data. I wanted a mechanism by which when new data was posted, any connected clients would receive a real-time notification (and data tables and charts in the client apps could be updated accordingly). SignalR with Service Bus scaleout proved to be the answer.

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.