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by Udi Dahan.
Original Post: Hype busting truth?
Feed Title: Udi Dahan - The Software Simplist
Feed URL: http://feeds.feedburner.com/UdiDahan-TheSoftwareSimplist
Feed Description: I am a software simplist. I make this beast of architecting, analysing, designing, developing, testing, managing, deploying software systems simple.
This blog is about how I do it.
1. Tight coupling has its place
2. Prefer explicit behavior over implicit
3. Services are the interface to business processes
The successes that I've seen on projects were those where business processes were designed across services. Those projects that took the discrete steps of each business processes and designed each step as a service, reusing those services between processes got mired down in integration, and often suffered horrible performance problems.
What I mean by "designed across services" is this:
One service would "hear" an event being published. It would perform some internal logic, and publish an event of its own. Another service would "hear" that event, and do something similar. This chaining of published events implemented one given business process. Other sequences of events embodied other processes. Changing a given process hardly ever changed service interaction, but rather was almost always implemented as a local change to logic internal to one service.
I would hardly describe this top-level design by using the phrase "Services are the interface to business processes". I don't think there really is an interface to a business process. A business process is what happens as a result of a given event and a pre-existing state. The same event, under a different pre-existing state, would probably cause different behavior - a different business process to occur.
About state, there really is no such thing. It is amorphous, changing all the time, never synchronized across all parties. When the first event occurs, the service that receives (and handles) that event is in state A, but the rest of the services' states are not known. Those services could already be handling other events, their states changing while the first service is doing its part of some business process.
My experience has been that this large-scale, concurrently running ecosystem of services is too complex to be modeled only in terms of flow-charted business processes. Business processes tell us how the ecosystem should behave in certain circumstances, but have not been effective design tools in my experience.
Command-and-control tactics that were once the mainstay of modern armies, are being replaced with more organic rules of engagement to respond more quickly to uncertain and changing battlefield conditions. It is time that we too give up the appearance of control found in orchestration and choreography in order to respond more quickly to the changing needs of business, lest we find ourselves extinct.
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