Topology

Messaging topology is a specific arrangement of the messaging entities, such as queues, topics, subscriptions, and rules.

Azure Service Bus transport operates on a topology created on the broker. The topology handles exchanging messages between endpoints, by creating and configuring Azure Service Bus entities.

The built-in topology, also know as ForwardingTopology, was introduced to take advantage of the broker nature of the Azure Service Bus and to leverage its native capabilities.

The topology creates a single input queue per endpoint and implements a publish-subscribe mechanism with all publishers using a single topic.

Subscriptions are created under the topic with one subscription entity per subscribing endpoint. Each subscription contains multiple rules; there's one rule per event type that the subscribing endpoint is interested in. This enables a complete decoupling between publishers and subscribers. All messages received by subscription are forwarded to the input queue of the subscriber.

ForwardingTopology

Quotas and limitations

The ForwardingTopology supports up to 2,000 endpoints with up to 2,000 events in total. Since multiple rules per subscriptions are used, topics cannot be partitioned.

Topology highlights

Decoupled Publishers / Subscribersyes
Polymorphic events supportyes
Event overflow protectionyes
Subscriber auto-scaling based on queue sizeyes
Reduced number of connections to the brokeryes

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