Jimmy Bogard / Chief Architect at Headspring
The greenfield project started out so promising. Instead of devolving into big ball of mud, the team decided to apply domain-driven design principles. Ubiquitous language, proper boundaries, encapsulation, it all made sense.
But along the way, something went completely and utterly wrong. It started with arguments on the proper way of implementing aggregates and entities. Arguments began over project and folder structure. Someone read a blog post that repositories are evil, and ORMs the devil incarnate. Another read that relational databases are last century, we need to store everything as a stream of events. Then came the actor model and frameworks that sounded like someone clearing their throat. Instead of a nice, clean architecture, the team chased the next new approach without ever actually shipping anything.
Beyond the endless technical arguments it causes, domain-driven design can actually produce great software. We have to look past the hype into the true value of DDD, what it can bring to our organizations and how it can enable us to build quality systems. With the advent of microservices, DDD is more important than ever – but only if we can get to the good parts.
Microservices are associated with extreme isolation (e.g. no shared database, autonomous dev-ops teams, etc.) At its best, this creates a practical boundary within which modeling and design have a chance to thrive. In Domain-driven Design (DDD) we call this a “Bounded Context”. Bounded contexts take many forms, some leakier than others, and the current best practices of microservices have given us perhaps the strongest mainstream manifestation of this principle to date. In this way, microservices can help teams who attempting DDD or other sophisticated approaches.Yet, as services get small and numerous, we might substitute one problem for another: The tangle of the monolith just migrates to become a tangle of interactions between microservices. Here, the strategic design principles of DDD can give architects a conceptual framework for working with suites of services and higher-level relationships between larger parts of systems.
This talk will introduce a few strategic design concepts and explain how they apply to development of microservices, as a tool for teams trying to grow large systems more coherently.