Hitchhiker's Guide to Software Architecture and Everything Else - by Michael Stal

Sunday, July 15, 2007

What the hell is an ESB?

When I am getting involved in discussions about SOA recently, ESB is one of those terms I often hear. ESB is another citizen of the SOA buzzword universe, comprising other TLAs such as BAM, BPM, EAI, or B2B. One of the most entertaining and fun exercises is asking senior management and other powerpoint engineers what exactly they mean by ESB. Guess, how many definitions of ESB you'll discover when asking this question? Once, business magazines such as the Wallstreet Journal start talking about SOA, you should be aware of the following facts:
  • senior management may soon ask your IT department for a SOA strategy
  • it may be the right time to sell shares of SOA vendors
  • you'll find all those market analysts attempting like crazy to convince you of the business impact of the aforementioned TLAs

Another fun part is talking to techno nerds about SOA, especially those who believe CORBA and the like will cure all world problems. Did you ever encounter this "I may not know your problem, but I know that CORBA is the right solution" habit? On one hand, these techno nerds will point you to all performance penalties caused by SOA, because they think SOA is all about WS-* standards only. On the other, they will prove that CORBA is SOA, because it already provides the same solution concepts such as separating interface from implementations and leveraging standardized protocols.

Nonetheless, SOA makes a lot of sense from a technology and from a business perspective. When integration of heterogeneous environments is a key issue in your product and solution development, SOA may be the appropriate choice. SOA is neither a ubiquitous solution for all networked systems as business managers often think, nor is it that inefficient as techno nerds believe. The reality lies somehow in the middle between these extremes. In fact, SOA is an architectural paradigm that may even be applicable for CORBA based solutions (but fits much better with message-oriented middleware, to be honest). Of course, SOA in its WS-* instantiation is a perfect alternative to EAI and BPM approaches.

When SOA started to evolve, it was considered a set of architectural concepts that must be implemented using a stack of low-level protocols (such as SOAP, WSDL, UDDI). This resembles how CORBA and DCOM started more than 15 years ago. For instance, the first CORBA products didn't even provide interoperability. They just offered the same standardized, uniform programming interface. To guarantee interoperability, the OMG introduced the IIOP (Internet Inter-ORB Protocol). Shortly after real world projects started integrating CORBA ORBs, they required advanced services to deal with events, security, discovery or transactions. Hence, the OMG initiated efforts to come up with the so-called COSS (Common Object Services Specification). The availability of COSS, however, did not solve all issues either, because engineers had to manually deal with CORBA ORBs as well as with a whole bunch of rather complex COSS services. In addition, not all vendors provided all the required services. Hence, the CCM (CORBA Component Model) was introduced that decouples developers from lifecycle management and service issues.

In the SOA/WS-* universe this storyline re-appears. Think of SOAP and WS-I (IIOP)! And think of WS-Coordination, WS-Attachments, WS-Security (COSS)! Finally, ask yourself which part of SOA is playing the role of advanced technologies such as CCM. This is exactly where ESB enters the stage. ESB is one of the core assets of any SOA strategy. It provides a container that decouples implementation details such as communication protocols from developers. It also adds (or should add) lifecycle management, routing, transformation, security, management and discovery services. Without an ESB, engineers have to face the challenge of dealing with a bunch of different (mostly low-level) technologies they need to integrate. Unfortunately, big players such as SAP or Microsoft do currently not provide integrated (!) ESB products. And those companies selling ESB solutions often provide "heavy-weight" containers with a high degree of vendor lock-in.

What we actually need are light-weight ESB solutions that are based upon standards such as SCA or OSGi and interoperate with other platforms (such as WCF/WF/BizTalk). Such ESB solutions should cover the whole range of application domains and support enterprise applications as well as embedded applications.

We have started our journey but it will take a long time to reach the destination.


  • Nice stuff about SOA inception

    By Blogger Unknown, at 6:12 AM  

  • Apache ServiceMix seems to on the right track, but imho the JBI specification should be based on OSGi instead of yet another lifecycle method.

    By Anonymous Anonymous, at 8:54 PM  

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