Service Bus messaging: flexible data delivery in the cloud
Service Bus is a brokered, or third-party communication mechanism. This is similar to a postal service in the physical world. Postal services make it very easy to send different kinds of letters and packages with a variety of delivery guarantees, anywhere in the world.
Service Bus supports two distinct messaging patterns: Azure Relay and Service Bus Messaging.
The WCF Relay component of Service Bus is a centralized (but highly load-balanced) service that supports a variety of different transport protocols and Web services standards
The relay service supports traditional one-way messaging, request/response messaging, and peer-to-peer messaging. It also
WCF Relay provides many benefits, but requires the server and client to both be online at the same time in order to send and receive messages
In contrast to the relay scheme, Service Bus Messaging, or brokered messaging can be thought of as asynchronous, or “temporally decoupled.” Producers (senders) and consumers (receivers) do not have to be online at the same time. The messaging infrastructure reliably stores messages in a “broker” (such as a queue) until the consuming party is ready to receive them
The core components of the Service Bus brokered messaging infrastructure are queues, topics, and subscriptions. The primary difference is that topics support publish/subscribe capabilities that can be used for sophisticated content-based routing and delivery logic, including sending to multiple recipients. These components enable new asynchronous messaging scenarios, such as temporal decoupling, publish/subscribe, and load balancing. For more information about these messaging entities, see Service Bus queues, topics, and subscriptions.