Recently I wrote about the fruitless plight of a schizophrenic service. Now, I think that some of that schizophrenia exists in the ESB too (or is it rubbing off onto the ESB?). I’ve always felt that the ESB was just another pattern that showed how to isolate things and deal with routing and transformations. The most common implementation was a messaging gadget with some pluggable framework of sorts for the transformations, and some configurable framework for routing.
With such isolation of parts, it was convenient to not worry about what happened elsewhere when something was thrown to this gadget for processing. And we started wondering about scalability things and decided that asynchronous was the way to go … disconnected, stateless, etc, all good, well-intentioned things and useful things.
Then the pattern became a product. And on top of this product we had more products like business process orchestrators or workflow managers. And below this product we had applications and databases and ftp locations and all sorts of things that catered for every imaginable protocol. And around all of this we had some enterprise-ish sort of management thing to keep on eye on everything that was happening inside this very busy product.
Then, services moved from applications to the ESB product. After all, it’s a service and that’s an enterprise service bus, right? And when the services where moved over to their new home, all the dependencies had to come along too. And then we started arguing about getting granularity right in the ESB. I used to just think that the ESB had a proxy of sorts to the service that still was at the application. Maybe I got it all wrong.
Now this ESB is starting to feel like an Application Server with a messaging gadget, workflow gadget, transformers, routers, protocol handlers. And some ESB’s have a web server too, since they have browser based management consoles.
Some people also like the idea of a rules engine for their complex domain rules and embedded those in their applications. Hold on, those content based routers in the ESB also used a rules engine. Ok, let’s move our rules over to the ESB too. Cool, my ESB is also a rules engine.
Now, I see people writing the most hellish XML that is meant to do everything from configure routing, define transformations, execute code, persist messages, fire off sets of rules and more. It reminds me so much of those weird and wonderful stored procedures and cascading triggers that we wrote. The other day I got a laugh out of a friend when I told him that ESB’s are now DB servers and everyone writes sprocs in XML.
And we tried to do everything in the database server – rules, custom types, defaults, constraints, sprocs, triggers, batch jobs … even jump into a shell and execute something else. It did not work out very well then.
If I was an ESB, I’d be very confused. I started life as a pattern with a reasonable implementation using messaging and transformation and routing. Now all of this. In fact, I’d be more stressed than confused.
Then again, maybe the ESB is not confused, and maybe the people that use the ESB that are confused. In fact, if I was one of those people, I’d be stressed too.