Currently it seems that receiving messages from a Service Bus Topic with an App Service that has been scaled-out (2 or more instances) requires jumping through hoops:
Subscribing to a Topic requires a preemptively created subscription.
If all instances share the same subscription messages are delivered to only one instance (as with a Queue).
This is not the desired behaviour!
Possible solution: create multiple subscriptions, configure every instance to use a different one.
This does not seem to be possible when using App Service.
One configuration is shared for all App Service instances.
Possible solution: every instance creates a subscription with a random name.
This requires that App Service instances have Service Bus credentials with MANAGE permission, which is dangerous.
This requires additional code that requires additional dependencies (on Azure Management API).
Please advise on a reliable way to listen to an Azure Service Bus Topic with a scaled-out (2+ instance) App Service using JMS, so that every message is received by every instance.