Publish / Subscribe #

When you Send a command shuttle needs to be able to determine the relevant endpoint. The same applies to publishing an event. Shuttle would need to know where to Publish the event to. When sending a command there should be 1, and exactly 1, endpoint that receives the command. When publishing, however, there can be 0 to any number of subscribers.

In order to register an endpoint as a subscriber you can either manually configure the subscription store, as recommended for production, or register the subscription using the ISubscriptionManager implementation:

var subscriptionManager = resolver.Resolve<ISubscriptionManager>();

// using type
subscriptionManager.Subscribe(typeof(Event1));
subscriptionManager.Subscribe(typeof(Event2));

// using a list of types
subscriptionManager.Subscribe(new[] { typeof(Event1), typeof(Event2) });

// using a full type name
subscriptionManager.Subscribe(typeof(Event1).FullName);
subscriptionManager.Subscribe(typeof(Event2).FullName);

// using a list of full type names
subscriptionManager.Subscribe(new[] { typeof(Event1).FullName, typeof(Event2).FullName });

// using a generic
subscriptionManager.Subscribe<Event1>();
subscriptionManager.Subscribe<Event2>();

var bus = IComponentResolver.Resolve<IServiceBus>().Start();

In a production environment it is recommended that the subscription store be maintained manually using an elevated identity. For the above one could use an identity that has read-only permissions. The Subscribe method will fail if the subscription does not exist. In this way one can ensure that the subscription is not missing from the relevant store.

Shuttle Configuration #

All endpoints that belong to the same physical pub/sub store should connect to the same store.

You would have a store for your development environment, perhaps even locally on your own machine. You would have a separate store for your QA, UAT, and production environments.

Publishing from a web-site #

Typically you would publish events from some processing endpoint, as opposed to a web-site.

That being said, there is nothing stopping you from publishing a message from a web-site. The idea behind publishing a message is that the message represents an event that is typically produced by some processing endpoint. Since a web application should not really be processing anything but rather be sending commands off to a processing endpoint it would stand to reason that a web application should not be publishing events.

So if you find yourself in a situation where it seems to make sense to publish from your web application it indicates that you need to make a design decision: either the design is not optimal (so the web application is performing processing) or you are constrained in some way the prohibits the implementation of a processing endpoint (maybe a shared hosting environment).