Is an Enterprise Service Bus (ESB) an important architectural piece to a Service-Oriented Architecture (SOA), or is it just vendor hype in order to sell a particular product such as SOA-in-a-box?

According to IBM.com, an ESB is a flexible connectivity infrastructure for integrating applications and services; it offers a flexible and manageable approach to service-oriented architecture implementation.

With this being said, it is my personal belief that ESBs are an important architectural piece to any SOA. Additionally, generic design patterns have been created around the integration of web services in to ESB regardless of any vendor.

ESB design patterns, according to Philip Hartman, can be classified in to the following categories:

• Interaction Patterns: Enable service interaction points to send and/or receive messages from the bus
• Mediation Patterns: Enable the altering of message exchanges
• Deployment Patterns: Support solution deployment into a federated infrastructure

Examples of Interaction Patterns:

• One-Way Message
• Synchronous Interaction
• Asynchronous Interaction
• Asynchronous Interaction with Timeout
• Asynchronous Interaction with a Notification Timer
• One Request, Multiple Responses
• One Request, One of Two Possible Responses
• One Request, a Mandatory Response, and an Optional Response
• Partial Processing
• Multiple Application Interactions

Benefits of the Mediation Pattern:

• Mediator promotes loose coupling by keeping objects from referring to each other explicitly, and it lets you vary their interaction independently
• Design an intermediary to decouple many peers
• Promote the many-to-many relationships between interacting peers to “full object status”

Examples of Interaction Patterns:

• Global ESB: Services share a single namespace and all service providers are visible to every service requester across an entire network
• Directly Connected ESB: Global service registry that enables independent ESB installations to be visible
• Brokered ESB: Bridges services that are reluctant to expose requesters or providers to ESBs in other domains
• Federated ESB: Service consumers and providers connect to the master or to a dependent ESB to access services throughout the network

References:

• Mediator Design Pattern. (2011). Retrieved 2011, from SourceMaking.com: http://sourcemaking.com/design_patterns/mediator
• Hartman, P. (2006, 24 1). ESB Patterns that "Click". Retrieved 2011, from The Art and Science of Being an IT Architect: http://artsciita.blogspot.com/2006/01/esb-patterns-that-click.html
• IBM. (2011). WebSphere DataPower XC10 Appliance Version 2.0. Retrieved 2011, from IBM.com: http://publib.boulder.ibm.com/infocenter/wdpxc/v2r0/index.jsp?topic=%2Fcom.ibm.websphere.help.glossary.doc%2Ftopics%2Fglossary.html
• Oracle. (2005). 12 Interaction Patterns. Retrieved 2011, from Oracle® BPEL Process Manager Developer's Guide: http://docs.oracle.com/cd/B31017_01/integrate.1013/b28981/interact.htm#BABHHEHD