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SOA & WOA: Article

Could Enterprises Be Pushing Back on ESBs?

Debate continues over messaging format viability

I just got back from the Gartner Application Integration show. This is perhaps the seventh of these conferences I attended, including the first one back in 1998. The good news is that the conference was packed and application integration seems to be making a strong resurgence with a little help from something called Web services. The bad news is that many of the attendees appeared confused, and the world of application integration and Web services/SOA seems more complex and difficult to grasp for the rank-and-file IT person than it was in the past. There don't seem to be as many clear answers these days, which is too bad because the problems seem to be getting bigger and integration is becoming a top-three IT priority according to the analysts.

The real surprise for me was the backlash against the concept of ESB (enterprise services bus) and its proper application within the enterprise as well as in the world of SOA. It seems to be falling off the current buzzword list as enterprises press forward with their SOA planning and implementation work, choosing more Web services?compliant messaging infrastructures instead.

In fact, I was most surprised to hear an analyst admit during a presentation that there was a flaw in the ESB concept, as end user organizations may over-integrate proprietary ESBs. This comment points to the fact that many ESBs will layer on top of existing messaging systems already in place, and may also be redundant with newer, more Web services?compliant approaches. In other words, you could end up with your traditional messaging system alongside your new ESB messaging system, as well as a new SOA infrastructure, all with redundant messaging capabilities.

The analysts could have a point there when considering the long-term strategic directions of SOAs. Indeed, many are calling ESBs "transitory" technology, something that will bridge enterprises to Web services, but perhaps not be the end solution.

Of course the ESB guys would argue that their ESB solution is indeed Web services/standards-based, albeit the underlying technology is based in Java or proprietary messaging systems. If you deal with the technology through standard interfaces, you should not be concerned with what happens behind the scenes. Moreover, they have all vowed to keep up with emerging Web services standards.

What's driving the debate even further is the appearance of new SOA infrastructure players with ESB-like capabilities, such as Blue Titan and their Network Director product with embedded queue technology in its Web services routers. Like the ESBs, they provide guaranteed message delivery, but they are also compliant with the current version of WS-ReliableMessaging.

The Essence of ESBs
I've heard the term ESB from both the analysts and vendors (both claiming ownership, by the way) to describe a technology stack that places service-oriented interfaces on top of messaging systems, such as JMS. Instead of invoking the Java interface to push and pull messages from a queue, you leverage a Web services interface. Going further, many of the ESB vendors have added "traditional EAI" features to their stacks, including transformation, routing, flow control, and process integration. Indeed, many have described ESB as kind of an EAI light.

Thus, those who employ an ESB would use it primarily for information-oriented integration, leveraging the ESB to move information between applications, which is traditionally the role of a messaging system. They also add transformation, routing, and other information brokering capabilities. However, most ESBs lack service- or behavior-based integration capabilities and the ability to effectively create and manage composite applications through this infrastructure. They do support simple orchestration, but again, typically around information movement.

The lack of true service-based integration is really the kicker for me when considering an ESB for use in an SOA. I believe the real value of creating an SOA and moving to Web services is the ability to reuse services inside and outside of an enterprise and create new applications by assembling services. This is how SOAs make you money. Also, SOAs provide us with the ability to create orchestration layers, abstracting services, and information flows for the purposes of creating business processes.

Thus, the purists are putting forth the argument that most SOAs should leverage pure Web services standards, otherwise integration and interoperability will be compromised. They further state that enterprises are going to double or triple up on messaging layers, implementing a JMS-based messaging system as well as a pure Web services?compliant messaging system at the same time. Moreover, ESBs typically exist with legacy messaging systems that are already in place. Furthermore, now that WS-ReliableMessaging is almost ready for primetime, as well as WS-Reliability (Sun's version, now ratified by OASIS), we're nearing the time when we can build Web services?compliant messaging systems without the need for an ESB. Thus SOA architects have other options today.

So, What's the Deal?
Clearly, building an SOA is one of the most confusing things to do these days. Not because the technology is so difficult to leverage; it's not, but there are many decisions to make, such as wading through competing technology as well as overlapping and numerous standards.

ESBs, at their essence, are reinvented messaging systems, but do have value for those who need messaging systems today and want tighter integration with their new service-based infrastructure. They do raise questions, however, as to their long-term value in light of newer, more Web services?compliant technology.

ESB vendors, however, are not going to stand around and watch their technology become irrelevant. Count on them to morph their product to meet changing expectations, including addressing emerging and existing Web services standards. Indeed, almost all ESB vendors have aligned with Web services standards, including WS-ReliableMessaging or WS-Reliability.

The key issue is that of fit. If you already have an existing enterprise middleware layer and are moving to service-oriented or Web services?compliant integration, leveraging an ESB is a step you may be able to skip. However, ESBs do seem to be a good fit for those enterprises performing simple information movement between stovepipes that don't need the heavy duty nature of more traditional integration technology. Once again, you have to map the appropriate technology to the problem, as well as consider longer-term strategic direction.

More Stories By David Linthicum

Dave Linthicum is Sr. VP at Cloud Technology Partners, and an internationally known cloud computing and SOA expert. He is a sought-after consultant, speaker, and blogger. In his career, Dave has formed or enhanced many of the ideas behind modern distributed computing including EAI, B2B Application Integration, and SOA, approaches and technologies in wide use today. In addition, he is the Editor-in-Chief of SYS-CON's Virtualization Journal.

For the last 10 years, he has focused on the technology and strategies around cloud computing, including working with several cloud computing startups. His industry experience includes tenure as CTO and CEO of several successful software and cloud computing companies, and upper-level management positions in Fortune 500 companies. In addition, he was an associate professor of computer science for eight years, and continues to lecture at major technical colleges and universities, including University of Virginia and Arizona State University. He keynotes at many leading technology conferences, and has several well-read columns and blogs. Linthicum has authored 10 books, including the ground-breaking "Enterprise Application Integration" and "B2B Application Integration." You can reach him at david@bluemountainlabs.com. Or follow him on Twitter. Or view his profile on LinkedIn.

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Most Recent Comments
Javier Camara 02/10/05 04:12:33 AM EST

I agree in that the ESB concept is not fully sound. For me, a SOA makes sense if it is view as a constellation of web services interacting among them. For this, something like a UDDI server is required for each service locating each other.

For me, all this (i.e. services + directory) is just enough if only synchronous communications are used. If asynchronous communications are needed, then you need also publish/subscribe and store-and-forward, i.e. roughly what a MOM does. You can call it an ESB if you want, although I think this concept in the market encompasses several roles:
1. Publish/subscribe to messages
2. Store-and-forward messages
3. Route messages
4. Transform messages

An interesting thing to note is to implement points 1. and 2. you do *not* need business logic, while to implement 3. and 4. you do.

As I said, I see roles 1 and 2 required in SOAs with asynchronous interactions.

Roles 3 and 4 are also needed in many cases, mainly for integrating disparate systems. However, my main point against an ESB is that, in order to perform these roles, you do *NOT* need of a new, special concept like the ESB. *Any* service in the constellation of services can perform both routing and transformation. It can range from being a single component like an ESB (which I think is a bad idea), or it can just be a set of services (e.g. a different service performing specific adaptation for a system being integrated).

For me, using a single ESB for 3. and 4. breaks the beauty of the SOA idea. You are supposed to made all your data and business logic of your organization available as services in order to be reused, and suddenly you put on top an ESB in which you put *more* business logic (routing and transformation). So my point is that this should be implemented just by means of regular services, and not by specific, central-piece new components called ESBs.

Now, if for implementing routing and transformation you want to use Tibco, WebSphere or whatever, fine - however, the logic created by these products should be at the same level as the other services in the SOA, and not above.

So I am not saying that orchestrating tools are not useful. They are. Only, they are not *imprescindible*; and at any rate they should be viewed just as more services in the SOA. However, this does not fit the marketing strategy of ESB vendors which show its ESB as an *enabler* of a SOA, instead of just one more *component* of it.