How to Split a Monolith: Service Architecture & Domain-Driven Design (DDD) - Speaker Deck

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How to Split a Monolith: Service Architecture & Domain-Driven Design (DDD) Joy Ebertz Sr Staff Engineer

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Today’s agenda • What do I mean by Service Architecture? • Why Worry About Service Architecture? • What is Domain-Driven Design or DDD? • What is Layered Architecture? • Mapping Back to Services

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What do I mean by Service Architecture? (In the context of this talk)

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Request API Gateway Authz Service AuthN Rate Limiting App Services Business Capability Services Foundational Capability Services Logging Event Bus Secrets Management Service Discovery

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Typical SOA Architecture Request API Gateway Authz Service AuthN Rate Limiting App Services Business Capability Services Foundational Capability Services Logging Event Bus Secrets Management Service Discovery

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Typical SOA Architecture App Services Business Capability Services Foundational Capability Services

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Why worry about Service Architecture?

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Code Repetition

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Code Repetition

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Code Repetition

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Hyper-localized Optimizations

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Chaos

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Chaos

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Chaos

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Chaos

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FE BE

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Domains/Bounded Contexts FE BE

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Layers FE BE

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What is Domain-Driven Design or (DDD)?

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DDD is an approach to developing software for complex needs by deeply connecting the implementation to an evolving model of the core business concepts.

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Since 2004

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Business Value over Technical Strategy DDD Principles

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DDD Principles Cross-functional Collaboration

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over Point Solutions DDD Principles

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Software Best Practices: Separation of Concerns DDD Principles

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Software Best Practices: Simplicity. DDD Principles

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DDD Principles

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DDD Core Concepts • Domains and Subdomains

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DDD Core Concepts • Domains and Subdomains • Bounded Contexts

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DDD Core Concepts • Domains and Subdomains • Bounded Contexts • Ubiquitous Language

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DDD Core Concepts • Domains and Subdomains • Bounded Contexts • Ubiquitous Language

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Domains & Subdomains DDD Core Concepts Problem Space

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Domains & Subdomains DDD Core Concepts

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Domains & Subdomains DDD Core Concepts

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Domains & Subdomains DDD Core Concepts

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Domains & Subdomains DDD Core Concepts

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Domains & Subdomains DDD Core Concepts

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Domains & Subdomains DDD Core Concepts

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Types of Subdomains: Core Subdomain

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Types of Subdomains: Supporting Subdomain

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Types of Subdomains: Generic Subdomain

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API Gateway Authentication Service Authorization Service Logging/Monitoring Contacting Customers (Email/Phone) (Feature Flags and A/B Testing)

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Core Subdomain Supporting Subdomain Generic Subdomain

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Core Subdomain Supporting Subdomain Generic Subdomain

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Core Subdomain Supporting Subdomain Generic Subdomain

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Core Subdomain Supporting Subdomain Generic Subdomain

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DDD Core Concepts • Domains and Subdomains • Bounded Contexts • Ubiquitous Language

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Domains

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Bounded Context

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The problem space is defined by a domain which consists of one or more subdomains.

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The problem space is defined by a domain which consists of one or more subdomains. The solution space is defined by a domain model which consists of one or more bounded contexts.

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Characteristics of Bounded Contexts

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Clear and Controlled Entry Points Bounded Context

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Clear and Controlled APIs Bounded Context

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Bounded Context

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Bounded Context

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Bounded Context

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DDD Core Concepts • Domains and Subdomains • Bounded Contexts • Ubiquitous Language

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Ubiquitous Language Domain Expert Marketing Developer

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Ubiquitous Language Domain Expert Marketing Developer Application Code Test Code Specs and Documentation Discussions & whiteboarding

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Subdomain Subdomain

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What is a file?

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Content Subdomain The container object that groups different versions of a piece of content and enables Box file- system capabilities. What is a file?

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Content Subdomain Storage Subdomain The container object that groups different versions of a piece of content and enables Box file- system capabilities. A blob of customer-owned data identified by a uniq_name. What is a file?

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Domains/Bounded Contexts FE BE

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Layers FE BE

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What is Layered Architecture?

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Layered Architecture is a way of dividing up an architecture between front-end, middle tier and back-end logic to optimize for decoupling and re-use.

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Application

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Application Business Capability

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Application Business Capability Foundational Capability

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Application Business Capability Foundational Capability Infrastructure Services

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Application Business Capability Foundational Capability Infrastructure Services

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Backend For Frontend (BFF)

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Your Servers Backend For Frontend (BFF)

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Your Servers FE Engineers BE Engineers Backend For Frontend (BFF)

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Your Servers FE Engineers BE Engineers Backend For Frontend (BFF)

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Your Servers FE Engineers BE Engineers Backend For Frontend (BFF)

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Backend For Frontend (BFF) Application Service FE Engineers

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Application Service Application Service Application Service Backend For Frontend (BFF)

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Application Service Application Service Application Service

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Application Business Capability Foundational Capability Infrastructure Services

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Business Capability Service

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Physical Store Race Expo Website Buy Running Shoes

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iPhone Buy Running Shoes

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iPhone Buy Running Shoes

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iPhone Buy Running Shoes Webapp

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iPhone Buy Running Shoes Webapp

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Application Business Capability Foundational Capability Infrastructure Services

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Single Source of Truth

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User Profile User Profile

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User Profile User Billing

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Application Business Capability Foundational Capability Infrastructure Services

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Often Generic Subdomains

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Mapping Back to Services

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Application Service Application Service

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Application Service Application Service Foundational Backend Service Business Capability Backend Service

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Application Service Application Service Foundational Backend Service Business Capability Backend Service

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Application Service Application Service Foundational Backend Service Business Capability Backend Service Backend Service

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Typical SOA Architecture Request API Gateway Authz Service AuthN Rate Limiting App Services Business Capability Services Foundational Capability Services Logging Event Bus Secrets Management Service Discovery

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Recap • Service Architecture • Domain-Driven Design or DDD • Layered Architecture • Mapping Back to Services Joy Ebertz @jkebertz [email protected]

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Thank you!

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Further Resources • Eric Evans’ classic DDD book that started it all (the ‘Blue Book’): Domain Driven Design: Tackling Complexity in the Heart of Software • Vaughn Vernon has a book a bit more on the practical side (the ‘Red Book’): Implementing Domain Driven Design • If you want something a bit shorter Vaughn Vernon also has a shortened version: Domain Driven Design Distilled • For another shorter, more reference driven option, Eric Evans also has: Domain Driven Design Reference • A former colleague recommends Scott Millett’s book: Patterns, Priciples, and Practices of Domain Driven Design DDD Books

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• Getting Started with Domain Driven Design: http://www.informit.com/articles/article.aspx?p=1944876&seqNum=5 • Strategic Domain Driven Design with Context Mapping: https://www.infoq.com/articles/ddd- contextmapping/ • My blog post, A Brief Intro to Domain Driven Design: https://austinstartups.com/a-brief-intro- to-domain-driven-design-326cf1669bbc • Is Design Dead? https://www.martinfowler.com/articles/designDead.html • How Can Domain-driven design help with large scale agile development? http://www.ben- morris.com/how-can-domain-driven-design-help-with-large-scale-agile-development/ DDD Articles Further Resources

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• Thoughtworks has a really great blog post about this topic: https://www.thoughtworks.com/insights/blog/well-factored-approach-securing-roi- your-service-investment-part-2 . Part 1 is here: https://www.thoughtworks.com/insights/blog/well-factored-approach-securing-roi-your- service-investment, but honestly most of the good material is in part 2. • The language in this one is a little bit different, but Mulesoft fundamentally talks about a lot of the same concepts: https://cloud.box.com/s/ggttm7wjsposhrcjxxzdmb3f4uxzp6mg • Another one by Mulesoft. This one doesn't directly talk about the horizontal splitting but does have a great diagram: https://www.linkedin.com/pulse/build-business-capabilities-apis- nial-darbey Layered Architecture Articles Further Resources

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• This also covers a lot more material, but in their Identifying Services section, IBM also touches on these concepts: https://www.redbooks.ibm.com/redbooks/pdfs/sg248357.pdf • This talks about more general layering principals, but has a lot of rules of thumb that still apply: https://www.linkedin.com/pulse/build-business-capabilities-apis-nial-darbey • Not directly about these concepts, but Jeff Coble's blog post is somewhat related and a good read: https://medium.com/@jeffcoble/from-product-to-platform-5d6857e55afb • My blog post (Microservices: Building things is easy, building the right thing is hard) also touches briefly on this: https://medium.com/box-tech-blog/microservices-building-things-is- easy-building-the-right-thing-is-hard-b88b6e2474c1 Layered Architecture Articles (continued…) Further Resources