How to Build Services from Legacy Applications
- by Chris Falter
The SOA consultants invaded the executive suite at your company or agency, preached the true religion, and converted the unbelievers. Now by divine imperative you must convert your legacy applications into a suite of reusable services. But as usual, you lack the time and resources that you need in order to develop the services properly. So you googled or bing’ed, found this blog post, and began crying in gratitude. Yes, as the title implies, I am going to reveal my easy, 3-step, works-every-time process for converting silos of legacy applications into the inventory of services your CIO has been dreaming about. So just close your eyes and count to 3 … now open them … and here it is…. Not. While wishful thinking is too often the coin of the IT realm, even the most naive practitioner knows that converting legacy applications into reusable services requires more than a magic wand. The reason is simple: if your starting point is your legacy applications, then you will simply be bolting a web service technology layer on top of your legacy API. And that legacy API is built in the image of the silo applications. Enter the wide gate of the legacy API, follow the broad path of generating service interfaces from existing code, and you will arrive at the siloed enterprise destruction that you thought you were escaping. The Straight and Narrow Path This past week I had the opportunity to learn how the FBI Criminal Justice Information Systems department has been transitioning from silo applications to a service inventory. Lafe Hutcheson, IT Specialist in the architecture group and fellow attendee at an SOA Architect Certification Workshop, was my guide. Lafe has survived the chaos of an SOA initiative, so it is not surprising that he was able to return from a US Army deployment to Kabul, Afghanistan with nary a scratch. According to Lafe, building their service inventory is a three-phase process: Model a business process. This requires intense collaboration between the IT and business wings of the organization, of course. The FBI uses IBM Websphere tools to model the process with BPMN. Identify candidate services to facilitate the business process. Convert the BPMN to an executable BPEL orchestration, model and develop the services, and use a BPEL engine to run the process. The FBI uses ActiveVOS for orchestration services. The 12 Step Program to End Your Legacy API Addiction Thomas Erl has documented a process for building a web service inventory that is quite similar to the FBI process. Erl’s process adds a technology architecture definition phase, which allows for the technology environment to influence the inventory blueprint. For example, if you are using an enterprise service bus, you will probably not need to build your own utility services for logging or intermediate routing. Erl also lists a service-oriented analysis phase that highlights the 12-step process of applying the principles of service orientation to modeling your services. Erl depicts the modeling of a service inventory as an iterative process: model a business process, define the relevant technology architecture, define the service inventory blueprint, analyze the services, then model another business process, rinse and repeat. (Astute readers will note that Erl’s diagram, restricted to analysis and modeling process, does not include the implementation phase that concludes the FBI service development methodology.) The service-oriented analysis phase is where you find the 12 steps that will free you from your legacy API addiction. In a nutshell, you identify the steps in the process that need services; identify the different types of services (agnostic entity services, service compositions, and utility services) that are required; apply service-orientation principles; and normalize the inventory into cohesive service models. Rather than discuss each of the 12 steps individually, I will close by simply referring my readers to Erl’s explanation.
