Competing-Consumers Messaging Pattern in Azure Service Bus

Question

I'm just getting started with Windows Azure Service Bus (Topics & Queues) and I'm trying to implement a Competing-Consumers messaging pattern.

Essentially, I want to have a set of message Producers and a set of message Consumers. Once a message is produced, I want the first available Consumer to process the message. No other Consumers should get the message.

Is there a way to do this in Azure?

Answer 1

You probably don't want Topics then, but rather Brokered Messaging.

You can emulate Topic-like functionality in Brokered Messaging by using the message's Label and/or Content Type properties along with the PeekLock receive mode.

Answer 2

Simple. Just make two (or more) receivers that concurrently receive from a single queue and you're done. Any retrieved message goes to exactly one of those receivers since the cursor over the mesasage log is advanced as a message is taken. Competing consumers are an inherent capability of a networked queue so there's really nothing special needed.

If you need the opposite - each message goes to each consumer - you make a subscrioption per consumer which gives you an isolated cusor over the message log that can move independent of other receivers. For kicks, you can obviously also have competing consumers on a subscription.

Clemens

Answer 3

Topics are a feature of brokered messaging, but are a one-to-many "publish/subscribe" pattern. Queues are one-to-one message communication. So yes, it sounds like you should simply use queues. Also see http://msdn.microsoft.com/en-us/library/hh689723(VS.103).aspx.