Entries Tagged 'esb' ↓

In 2002 Sonic Software invented the term ESB to differentiate their middleware from everyone else’s middleware. This is an old marketing tactic when you can’t differentiate your product from the others – just invent a new category. To lend credence, you need the collusion of an analyst and Gartner was there to knock this marketechture into the hype-stratosphere. We can also thank Sonic for the crap notion that an “ESB is a prebuilt SOA“.

ESBs have been back in the news again with the usual attendant vitriol and this has revived the perpetual question – “what is an ESB and why do I need one“?

I’ve seen ESBs referred to in two rather broad contexts. The first context refers to a distributed infrastructure that allows your Service Providers and Service Consumers to find each other and work together in a scalable and loosely coupled manner. This is often referred to as the “ESB as design pattern” and I think it is what many people would like ESB to mean. This “Service Bus” is effectively an extension of the “Message Bus” concept and is what I had in mind when I wrote about this subject a while ago.

The second context is ESB as a tool or a “thing you buy from a vendor” and this seems to be the terminology that calls forth all manner of vituperations. In this context ESB is secret marketing code for what used to be called “integration middleware.” This is also the thing that Jim Webber calls the “Erroneous Spaghetti Box.”

In this context, the eternal ESB question becomes – “in an SOA world, do I really need integration middleware?” I really think you can make more sense of the ESB debate by recasting into this terminology. The SOA pragmatists (including myself) see that there is a role for “integration middleware” as tools within your SOA infrastructure.

Eric Roch thinks of an ESB as a “productivity tool for integration” and points out that The legacy integration problem hasn’t gone away yet.

ZapThink say that an ESB could play the role of a Service Intermediary where transformations and content-based routing are essential requirements.

Todd Biske characterises five different types of ESB product each supporting different functions such as legacy integration, orchestration, mediation and transport, SOAP wrapping and gateways. The key insight here is how the label “ESB” has come to be applied to so many disparate products. “ESB” has come to mean everything and nothing and should be banished from our vocabulary.

So I agree with the pragmatists – design your SOA infrastructure to support your business requirements. Consider the so-called ESB products as tools and if you need mediation, or orchestration or transformation or integration to legacy systems then consider using the scads of tools – both proprietary and opensource – out there that support this stuff. And whatever you do, don’t try to author XSLT using Notepad.

In my last post on this topic I talked about the concept of an ESB. Here I talk about why you would want one.

There are plenty of whitepapers, analyst reports and vendor statements about the features and functions of the various ESB products. In my experience, the key advantages of using an ESB are less about features and functions and more about how you use it.

Standardization

One of the primary advantages of an ESB is that it gives you a standardized platform for integration. When everyone is using the same tools you can develop enterprise-wide frameworks, patterns and best practices for building re-usable services. Without a unifying platform, you get a divergence of integration methods which leads to inconsistency and higher cost of management and change. So an ESB platform helps with design-time governance. Note that this is not the same as standardization in the sense of using web-services standards. The important thing is that you use the ESB to support your own enterprise standards. These may be based on external standards – but that may be of secondary importance.

Loose Coupling

The bus architecture of an ESB encourages you toward a loosely coupled architecture.

• Physically decoupled by making use of message passing mechanisms (e.g. JMS) versus direct network connections (e.g. HTTP).
• Semantically decoupled by use of message transformation so that services are exposed in a system-neutral format which reduces application lock-in and reduces the cost of change.

Scalability and Reliability

Physical loose-coupling provides scalability advantages such as high-availability, fault-tolerance and load balancing. The messaging layer in the ESB directs messages between service endpoints to the appropriate instance of the endpoint. For example, in the event of a service provider failure, messages will be redirected to a backup provider – thus supporting high availability. In the case of load balancing, messages are distributed between redundant providers (or consumers) to handle high volumes of message traffic. You could say that physical loose-coupling supports change at the “micro” level where short term changes in the system topology can be compensated for via real-time message redirection.

Routing and mediation

Message routing supports scalability and fault tolerance. An ESB can also be used to support business-level routing and mediation. For example content-based routing allows services to be invoked based on the content of a service request. A business example would be routing of a customer enquiry to the branch where that customer account is located. A technical example would be the routing of a service request based on the version of the service being invoked.

Complex message exchange patterns

Traditional HTTP-based services support only one-to-one request-reply MEPs. An ESB supports more complex MEPs such as asynchronous one-way messaging and to multiple subscribers using topic-based messaging. Asynchronous publish and subscribe mechanisms support new ways of intermediating service consumers and subscribers – such as auditing, service monitoring – which are extremely useful for runtime management and governance of your services. Beyond mere governance, higher level business functions such as complex event processing (CEP) and business activity monitoring (BAM) are supported by this ability to “listen in” to service traffic on the ESB.

The benefits of an ESB that I’ve described above stem largely from the architecture of an ESB and in particular from the use of a message bus as the primary underlying transport. But it is important to understand that these benefits don’t automatically come “out of the box”. Your solution architecture (and your architects) must recognise and utilise the architectural principles underlying the ESB.

A question I often get is “what is an ESB and why do I need one”? This question is motivated by a number of concerns; non-technical people have heard the term but don’t understand the concept, semi-technical people are trying to figure out conflicting vendor definitions, and technical people are confused by the debate between different service enablement approachs – RESTful versus ws-* versus middleware-supported hybrids.

The Elevator Pitch

A service bus provides a uniform and consistent platform to allow service providers and service consumers to interoperate. An ESB provides benefits such as:

• standardization
• loose coupling
• resilience and high availability
• monitoring and intermediation

Hardware

I’m not sure of the provenance of the word “bus” as it is applied in the technical domain (I’m sure there is some interesting etymology there) but you can confidently trace it back to the concept of a computer hardware bus. The idea of a hardware bus (or backplane) is that hardware components – such as sound-cards, video cards, floating point accelerators, tape-drives, barcode scanners etc – can all slot into and interoperate through a shared infrastructure. By supporting a standard hardware interface and a standard software protocol, the hardware bus abstracts the details of each individual hardware component. The key features of the harwdare bus are:

• standardized hardware connectivity to the backplane
• standardized software protocol between each component and the backplane
• hardware components can operate independently without having to know details about each other
• a single infrastructure replaces multiple point-to-point connections between components (i.e. does away with a lot of ad hoc soldering).

Software

Networked systems arrived in the seventies and grew out of control in the eighties. Early network infrastructures such as Unix sockets were hard-wired point-to-point affairs with little or no abstraction of the the two programs that were working together.

The idea of a software bus is that software components can work together – yet independently – via a standardized message passing mechanism that would abstract away the need to create individual network connections between components. The software bus would take care of routing messages to the required location and also take care of all that hard stuff like quality-of-service, reliability and scalability. This is equivalent to standardizing the “hardware connectivity” in the hardware bus. TIBCO’s predecessor – Teknekron – articulated the concept of the software bus in the early nineties

The Service Bus

So the hardware bus standardizes hardware connectivity and the software bus standardizes software connectivity. The Service Bus has refined the concept of the software bus by taking a more service-oriented approach and adding support for the XML stack underlying web services and transport connectivity (e.g. bridging HTTP to JMS).

So why do you need an ESB? More on that anon…