Tackle Business Complexity in a Microservice with DDD and CQRS Patterns
Tip
This content is an excerpt from the eBook, .NET Microservices Architecture for Containerized .NET Applications, available on .NET Docs or as a free downloadable PDF that can be read offline.
Design a domain model for each microservice or Bounded Context that reflects understanding of the business domain.
This section focuses on more advanced microservices that you implement when you need to tackle complex subsystems, or microservices derived from the knowledge of domain experts with ever-changing business rules. The architecture patterns used in this section are based on domain-driven design (DDD) and Command and Query Responsibility Segregation (CQRS) approaches, as illustrated in Figure 7-1.
Difference between external architecture: microservice patterns, API gateways, resilient communications, pub/sub, etc., and internal architecture: data driven/CRUD, DDD patterns, dependency injection, multiple libraries, etc.
Figure 7-1. External microservice architecture versus internal architecture patterns for each microservice
However, most of the techniques for data driven microservices, such as how to implement an ASP.NET Core Web API service or how to expose Swagger metadata with Swashbuckle or NSwag, are also applicable to the more advanced microservices implemented internally with DDD patterns. This section is an extension of the previous sections, because most of the practices explained earlier also apply here or for any kind of microservice.
This section first provides details on the simplified CQRS patterns used in the eShopOnContainers reference application. Later, you will get an overview of the DDD techniques that enable you to find common patterns that you can reuse in your applications.
DDD is a large topic with a rich set of resources for learning. You can start with books like Domain-Driven Design by Eric Evans and additional materials from Vaughn Vernon, Jimmy Nilsson, Greg Young, Udi Dahan, Jimmy Bogard, and many other DDD/CQRS experts. But most of all you need to try to learn how to apply DDD techniques from the conversations, whiteboarding, and domain modeling sessions with the experts in your concrete business domain.
Additional resources
DDD (Domain-Driven Design)
Eric Evans. Domain Language
https://domainlanguage.com/Martin Fowler. Domain-Driven Design
https://martinfowler.com/tags/domain%20driven%20design.htmlJimmy Bogard. Strengthening your domain: a primer
https://lostechies.com/jimmybogard/2010/02/04/strengthening-your-domain-a-primer/Distributed Domain-Driven Design webinar
https://particular.net/webinars/ddd-design-no-nonsense-implementation-guide
DDD books
Eric Evans. Domain-Driven Design: Tackling Complexity in the Heart of Software
https://www.amazon.com/Domain-Driven-Design-Tackling-Complexity-Software/dp/0321125215/Eric Evans. Domain-Driven Design Reference: Definitions and Pattern Summaries
https://www.amazon.com/Domain-Driven-Design-Reference-Definitions-2014-09-22/dp/B01N8YB4ZO/Vaughn Vernon. Implementing Domain-Driven Design
https://www.amazon.com/Implementing-Domain-Driven-Design-Vaughn-Vernon/dp/0321834577/Vaughn Vernon. Domain-Driven Design Distilled
https://www.amazon.com/Domain-Driven-Design-Distilled-Vaughn-Vernon/dp/0134434420/Jimmy Nilsson. Applying Domain-Driven Design and Patterns
https://www.amazon.com/Applying-Domain-Driven-Design-Patterns-Examples/dp/0321268202/Cesar de la Torre. N-Layered Domain-Oriented Architecture Guide with .NET
https://www.amazon.com/N-Layered-Domain-Oriented-Architecture-Guide-NET/dp/8493903612/Abel Avram and Floyd Marinescu. Domain-Driven Design Quickly
https://www.amazon.com/Domain-Driven-Design-Quickly-Abel-Avram/dp/1411609255/Scott Millett, Nick Tune - Patterns, Principles, and Practices of Domain-Driven Design
https://www.wiley.com/Patterns%2C+Principles%2C+and+Practices+of+Domain+Driven+Design-p-9781118714706
DDD training
- Julie Lerman and Steve Smith. Domain-Driven Design Fundamentals
https://www.pluralsight.com/courses/fundamentals-domain-driven-design
