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Chris Richardson on Domain-Driven Microservices Design

In this week’s podcast, Thomas Betts talks with Chris Richardson, a developer, architect, Java Champion and author of POJOs in Action. Before his workshop on Microservices w/ Spring Boot and Docker at QCon San Francisco 2016, Richardson took time to discuss his ideas on how to use DDD and CQRS concepts as a guide for implementing a robust microservices architecture. You can also watch his  related presentation “Developing Microservices with Aggregates”.

Key Takeaways

Show Notes

Microservices vs. Microservices Architecture

  • 1m:50s - @crichardson tweet: "Microservice architecture" is a better term than "microservices". The latter suggests that a single microservice is somehow interesting.

System Decomposition Following Domain-Driven Design

  • 4m:16s - Decomposing a system into a set of microservices is related to understanding business capability and subdomain.
  • 5m:16s - If you decompose your system in the wrong way, you’re making a mistake at an architectural level. The worst case is a distributed monolith.
  • 6m:34s - In DDD terms, each service is itself a bounded context, with its own domain model and ubiquitous language.
  • 8m:33s - The “fuzzy stuff” in the DDD book, such as bounded contexts, directly apply to a microservices architecture.
  • 10m:26s - One DDD constraint is that a transaction can only create or update a single aggregate. In practice, this means microservice architectures cannot have distributed transactions.
  • 11m:13s - If you want to do microservices properly, read the DDD book.

Microservice Boundaries, EDA and CQRS

  • 11m:51s - Microservices must be loosely coupled, usually creating a model with one database per service.
  • 12m:45s - There is a business requirement to maintain data consistency across services, and using an event driven architecture is a good way to achieve that.
  • 13m:38s - Event sourcing is specific technique for persisting domain objects as a series of events.
  • 14m:11s - Just as transactions don’t like to be split across microservices, queries cannot simply join across multiple data sources. CQRS provides a solution that accommodates querying via microservices and materialized views.

Replacing a Monolith

  • 17m:27s - Microservices are not a silver bullet, nor a free lunch. MSA comes with complexity, ranging from data management to deployment.
  • 20m:00s - When does it make sense to make the transition from a monolith to an MSA?
  • 20m:35s - MSA is a solution to a problem. With an existing monolith, if are you unhappy with the rate of development, or the pain associated with making changes, then microservices are probably the solution.
  • 22m:29s - When moving to microservices, definitely do not do a big bang rewrite -- take an iterative approach, incrementally refactoring your monolith into a set of services.
  • 24m:16s - Implementing microservices can utilize new, cool technology, but always remember the purpose of writing an application is to automate critical business processes. Domain-Driven Design can help develop the business logic at the core of your system.

Technology Concepts Discussed

Books Mentioned

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