Signalr on Azure: service bus required for calling a single client?

Question

I read that Signalr on Azure requires a service bus implementation (eg https://github.com/SignalR/SignalR/wiki/Azure-service-bus ) for scalability purpose.

However, my server only makes callbacks to a single client (the caller):

// Invoke a method on the calling client
Caller.addMessage(data);

If don't need Signalr's broadcasting functionality, is an underlaying service bus still necessary?

Answer 1

The Service Bus dependency is not something specific to Azure. Any time you have multiple servers in play, some of your signalR clients will have created their connection to a specific server. If you want to keep multiple servers in sync something needs to handle the server to server real time communication. The pub-sub model of service bus lines up with this requirement quite well.

dfowleR lists a specific case of this in the comments. Make sure you read down that far!

If you are running on a single server (without the sla on Azure) signalR will work just fine on a Cloud Service Web Role as well as the new Azure Web Sites. I did a screencast on this simple scenario that does not take on a service bus dependency, but only runs on a single server.

Answer 2

In order to support the load balance scenario, is it possible to enstablish a "server to server" SignalR PersistConnection between multiple instances (ie on Azure) ? If so, we can use a SQL Azure Table where all instances register at startup, so newest can connect to previous ones.