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Home > Design Patterns > Event-Driven Messaging

Event-Driven Messaging (Little, Rischbeck, Simon)

How can service consumers be automatically notified of runtime service events?

Problem

Events that occur within the functional boundary encapsulated by a service may be of relevance to service consumers, but without resorting to inefficient polling-based interaction, the consumer has no way of learning about these events.

Solution

The consumer establishes itself as a subscriber of the service. The service, in turn, automatically issues notifications of relevant events to this and any of its subscribers.

Application

A messaging framework is implemented capable of supporting the publish-and-subscribe MEP and associated complex event processing and tracking.

Impacts

Event-driven message exchanges cannot easily be incorporated as part of Atomic Service Transaction, and publisher/ subscriber availability issues can arise.

Principles

Standardized Service Contract, Service Loose Coupling, Service Autonomy

Architecture

Inventory, Composition

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Event-Driven Messaging: Service A requests that it be set up as a subscriber to the event it is interested in by interacting with an event manager. Once the event occurs, Service B forwards the details to the event manager which, in turn, notifies Service A (and all other subscribers) via a one-way, asynchronous data transfer. Note that in this case, Service A also receives the event information earlier because the event details can be transmitted as soon as they're available.

Service A requests that it be set up as a subscriber to the event it is interested in by interacting with an event manager. Once the event occurs, Service B forwards the details to the event manager which, in turn, notifies Service A (and all other subscribers) via a one-way, asynchronous data transfer. Note that in this case, Service A also receives the event information earlier because the event details can be transmitted as soon as they're available.

This page contains excerpts from:

SOA Design Patterns by Thomas Erl

Foreword by Grady Booch

With contributions from David Chappell, Jason Hogg, Anish Karmarkar, Mark Little, David Orchard, Satadru Roy, Thomas Rischbeck, Arnaud Simon, Clemens Utschig, Dennis Wisnosky, and others.

(ISBN: 0136135161, Hardcover, Full-Color, 400+ Illustrations, 865 pages)

For more information about this book, visit www.servicetechbooks.com.