Communication between a WebJob and SignalR Hub

Question

I have the following scenario:

I have an azure webjob (used to send mails) and I need to check the progress of the webjob in my web application.
I am using SignalR to communicate with clients from my server.
When I want to send an email, I push a message in the queue and the azure webjob does his job.

The question is, how can I communicate the progress of the webjob to the client? Originally my idea was to push a message from the webjob, so the Hub could read it from the queue. Then, I would notify clients from the hub. However, I am not able to find a way to communicate the webjob and the hub, I do not know how to trigger an action in the hub when a message is pushed into the queue or in the service bus. That is to say, I dont know how to subscribe the hub to a certain message of the queue.

Can someone help me with it?

Have you been successful with this task? – Artyom Mar 12 '18 at 14:04 — Artyom, Mar 12 '18 at 14:04

score 14 · Accepted Answer · answered Sep 01 '15 at 02:30

14

The way that I have done it is to set up the webjob as a SignalR client, push messages via SignalR from the webjob to the server, then relay those messages to the SignalR web clients.

Start by installing the SignalR web client (nuget package ID is Microsoft.AspNet.SignalR.Client) on your webjob.

Then in your webjob, initialise your SignalR connection hub and send messages to the server, e.g.:

public class Functions
{
    HubConnection _hub = new HubConnection("http://your.signalr.server");
    var _proxy = hub.CreateHubProxy("EmailHub");

    public async Task ProcessQueueMessageAsync([QueueTrigger("queue")] EmailDto message)
    {
        if (_hub.State == ConnectionState.Disconnected)
        {
            await _hub.Start();
        }

        ...

        await _proxy.Invoke("SendEmailProgress", message.Id, "complete");
    }
}

Your SignalR server will receive these messages and can then relay them to the other SignalR clients, e.g.:

public class EmailHub : Hub
{
    public void SendEmailProgress(int messageId, string status)
    {            
        Clients.All.broadcastEmailStatus(messageId, status);
    }        
}

answered Sep 01 '15 at 02:30

Teppic

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Also note that the `HubConnection` allows you to add additional headers, such as **Authorization** headers, which means that you can also secure the communication between the webjob and Notification Hub. – Brendan Green Sep 01 '15 at 04:24
By the way _proxy.Invoke() has to have the exact same number of attributes the invoked method has, no matter if they are optional or not. My error (not hitting the method and throwing exception) was caused by ommiting the optional parameters. – podvlada Oct 21 '16 at 13:58
That was 3 years ago. Probably now there is a better solution? – Artyom Mar 12 '18 at 13:30
@teppic and if we have multiple signalr servers behind Traffic Manager? Ie. "http://your.signalr.server" resolves to not busy one by Traffic Manager but not to those ones with clients to reach. Then this will fail to send "email progress" to those. – Artyom Mar 12 '18 at 14:03

Communication between a WebJob and SignalR Hub

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