Publish

The simplest messaging pattern that AzureNetQ supports is Publish/Subscribe. This pattern is an excellent way of de-coupling providers of information from consumers. The publisher simply says, ‘This has happened’ or ‘I now have this information’, to the world. It doesn’t care if anyone is listening or who they might be or where they are located.

AzureNetQ uses Service Bus Topics/Subscriptions as it's underlying transport mechanism for Publish/Subscribe.

We can add and remove subscribers for a particular message type without any reconfiguration of the publisher. We can also have many publishers publishing the same message, again adding and removing publishers without having to reconfigure any of the other publishers or subscribers.

To publish with AzureNetQ (assuming you've already created an IBus instance):

1. Create an instance of your message, it can be any serializable .NET type.
2. Call the Publish method on IBus passing it your message instance.

Here's the code...

var message = new MyMessage { Text = "Hello Service Bus" };
bus.Publish(message);

Unlike RabbitMQ where you need to enable publisher confirms for guaranteed delivery notification, if the service bus broker responds without error then you can be sure that your message has been persisted and will be delivered to any subscribers.

###A warning

The actors in the Publish / Subscribe pattern are ignorant of each other. a publisher is simply saying to the world 'this has happened', a subscriber is telling the world 'I care about this'. In this model it's fine for no one to care about a particular event. There might be one subscriber for a message, there might be 200, or there might be none. The publisher shouldn't care.

AzureNetQ implements this pattern. If you start publishing and no subscribers have ever been started then your messages simply disappear. This is by design.