Tuesday, October 23, 2007

SOA Technology Best Practice

Let me formalise what's on my mind regarding SOA best practice.

  1. Build your core application using the principles of Domain-Driven Design. This is your service implementation. Hint: If using Java, Spring/JPA is the way to go. EJBsaurus is dead.
  2. Take the help of an off-the-shelf domain model like IFW for Banking and IAA for Insurance. This will let you build incrementally without experiencing refactoring pain as your model grows.
  3. If the way your clients refer to your services emphasises verbs over nouns ("Jelly this eel"), you may want to look at SOAP-based Web Services, which are operation-oriented services. If your clients emphasise nouns over verbs ("Buy a ticket to the Spice Girls concert"), consider REST-based Web Services, which are resource-oriented services.
  4. Model your interface contract using XML schema in either case. Layer SOAP or REST Data Interchange patterns over this basic XML document foundation.
  5. Follow Contract-First Design. Do not generate your service interface from your implementation classes, even if your vendor gives you cool tools to do so painlessly (Hint: the pain comes later, when every change to your implementation breaks your service contract).
  6. Use a meet-in-the-middle mapping approach to connect the XML documents in the contract to the domain model. Do not generate implementation classes from the service interface. The self-important JAXB library is a bad bug that's going around. Use JiBX or TopLink instead.
  7. When building the Presentation Tier of an application that consumes services, use the SOFEA model.
  8. If you want to do content aggregation using 2007 thinking, consider a mashup. If still stuck in 2003, use a portal server and jump through the associated hoops.
  9. You don't need an ESB product, not now, not ever. Learn to see the "bus" in the way services are built and invoked. Remember that the web with its smart endpoints has comprehensively beaten the telco network with its smart network approach, even in voice communications. If you must use an ESB, deploy it in a decentralised, "smart endpoints" configuration. Obviously, a decentralised ESB is economically viable only with an Open Source product . A commercial one will force you to deploy it in a centralised architecture to save on licence costs (blech!).
  10. You don't need an ESB product to do process orchestration either. Use BPEL engines at endpoints. If you need human workflow, use BPEL4People.
  11. Open Source is the way of the future. Wake up and smell the coffee. For SOAP-based Web Services, consider Sun's Metro (formerly Tango) SOAP stack. For REST, consider Sun's Jersey (Java-based) or SnapLogic (Python-based). For an ESB (decentralised, of course), consider ServiceMix/CeltiXFire/FUSE. For process orchestration, including human workflow, check out Intalio.
  12. Management of your services can be centralised even with decentralised services. That's not an argument for a centralised ESB either.
  13. Take vendor education with a pinch of salt. Talk to fellow practitioners, especially the bold and the irreverent.


Mike Davison said...

Very insightful post. Its all too easy to fall into the vendor driven architecture nightmare with SOA. Discussion like this shows that this doesn't always have to be the case.

Subbu said...

I like the last point best about being wary of vendor evangelism.