CODEWITHSUNDEEP
c#.netsignalrnservicebusazureservicebus
Alwyn
Alwyn

Reputation: 8337

Calling SignalR client from webfarm

I have the following message transport scenarios

Client -> Calls SignalR -> Calls NServiceBus -> Process Message internally -> Calls NServiceBus Gateway service with Result -> Calls SignalR Hub -> Updates the client with result.

In choosing whether to use SignalR vs. long polling, I need to know if SignalR is scaleable. So in doing my homework I came across SignalR on Azure Service Bus. The setup is done on the Global.asax application start.

Ultimately I need to be able to do this, from inside an NServiceBus handler:

        var context = GlobalHost.ConnectionManager.GetHubContext<MyHub>();
        context.Clients.Group(group).addMessage(message);

The question is if context will be jacked up, because I'm (potentially) calling it from another machine than the one the client was connected to?

Also what is the sharding schema that the SignalR implementation uses to seed the topics? I know I can configure it to use N-number of topics, but how is it actually determining which message goes to which topics and if it's relevant from an external caller PoV.

Upvotes: 1

Views: 542

Answers (1)

halter73
halter73

Reputation: 15244

You should be able to use GlobalHost.ConnectionManager.GetHubContext in any application where you have registered ServiceBusMessageBus as your IMessageBus via SignalR's GlobalHost.DepenencyResolver. This is done for you if you call GlobalHost.DepenencyResolver.UseServiceBus(...) in the application.

If you do this, a message will be published to Azure Service Bus for each call to addMessage or any other hub method on the IHubContext returned from GetHubContext. If there are subscribed clients connected to other nodes in the web farm, the other nodes will pick up the message from Service Bus and relay it to the subscribed clients.

Which topic a message goes to should not be relevant from the PoV of an external caller. You can use multiple topics to improve throughput, but for most use cases one should be sufficient.

If you choose to use more than one topic, you can think about the topic a message goes to as being essentially random. The only thing that is guaranteed is that messages from the same sender will go to the same topic. This allows SignalR to keep messages from the same sender in order.

Caveat emptor: SignalR has not yet had an official release supporting scale out. The 1.1 version will be the first release to support scale out officially.

Upvotes: 1

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