Introduction au DDD sous l’angle stratégique — hyf mai 2020

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www.lilobase.me The strategies behind DDD @lilobase #MeetupDeconﬁnement lgo.group

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Let’s start a new project !

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Let’s start a new project ! We just receive the customer’s requirements, we still need to clarify a few things. But you can start the preliminary design phase ! Let's do a sprint zero !

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SQL or NoSQL ? Java or C# ? Spring Boot or Quarkus ? PostgreSQL or MySQL ? Kafka or Redis ? Microservices or Monolith ? Kubernetes or Nomad ? Angular or React ?

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What are you working on ? There are still some uncertainties, but we’re gonna use kafka …

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Java or C# ? PostgreSQL or MySQL ? Kafka or Redis ? Microservices or Monolith ? Kubernetes or Nomad ? SQL or NoSQL ? Spring Boot or Quarkus ? These issues address only the solution

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Java or C# ? PostgreSQL or MySQL ? Kafka or Redis ? Microservices or Monolith ? Kubernetes or Nomad ? SQL or NoSQL ? Spring Boot or Quarkus ? These issues address only the solution But not the problem What should we do ?

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These issues address only the solution But not the problem What should we do ? How are we going to do it ?

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These issues address only the solution And that's why we keep being treated as technical specialists

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These issues address only the solution It is an important discussion to have But not the problem But only after we've ﬁgured out what to do

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These issues address only the solution And are the hardest to refactor

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Let’s rewind

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Let’s start a new project !

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Let’s start a new project ! We just receive the customer’s requirements, we still need to clarify a few things. But you can start the preliminary design phase ! Let's do a sprint zero !

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I heard about « Domain Driven Design », maybe we should use it ! Yeah, that's a great idea.

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Aggregate Repository Bounded Context as Microservices Domain Service Event Driven CQRS Entity Value Object Hexagonal Architecture

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What are you working on ? There are still some uncertainties, but we’re gonna use an event-driven hexagonal architecture …

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These issues still address only the solution Aggregate Repository Bounded Context as Microservices Domain Service CQRS Entity Value Object Hexagonal Architecture Event Driven

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These issues still address only the solution This is what we call « DDD Lite »

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These issues still address only the solution And that's why we keep being treated as technical specialists

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www.lilobase.me DDD is all about Alignment @lilobase

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DDD is all about Alignment What should we do ? How are we going to do it ?

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DDD is all about Alignment What should we do ? How are we going to do it ?

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Domains & Subdomains Business Domain discovery THE Software Authoring & Publishing Printing & Supply Chain Customer Care Retail Store You need to acknowledge the fact that you have several domains

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Retail Store Inventory Customer Care Shipping Only one VP should be angry at a time Retail Store Inventory Customer Care Shipping Authoring & Publishing Printing & Supply Chain Customer Care Retail Store Domains & Subdomains Business Domain discovery

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Retail Store Inventory Customer Care Shipping These are neither Bounded Contexts nor Microservices Authoring & Publishing Printing & Supply Chain Customer Care Retail Store Domains & Subdomains Business Domain discovery

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Retail Store Inventory Customer Care Shipping These are your domains Authoring & Publishing Printing & Supply Chain Customer Care Retail Store Domains & Subdomains Business Domain discovery

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Your domains contain domains Domains & Subdomains Business Domain discovery Online Retail Store Payment processor Catalogue Invoicing

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Domain Mapping Business Domain Classiﬁcation Authoring Plateform Publishing & Printing Inventory Management Payment Processor Catalogue Invoicing Shipping Order Processing Proofreading

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Supporting Subdomain Generic Subdomain Core (sub)Domain Key differentiator Domains & Subdomains Business Domain Classiﬁcation Essential to the organization’s success Required for the organization’s success Critical to the organization’s success

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Domains & Subdomains Business Domain Classiﬁcation Authoring Plateform Inventory Management Shipping Payment Processor Catalogue Invoicing Order Processing Publishing & Printing Proofreading

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Domains & Subdomains Business Domain Classiﬁcation Authoring Plateform Inventory Management Payment Processor Catalogue Invoicing Each business context is speciﬁc Shipping Order Processing Publishing & Printing Proofreading

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Authoring Plateform Domains’ Connexion Reveal Business Relationships Inventory Management Shipping Catalogue Invoicing Order Processing Payment Processor It can highlight signiﬁcant sub-domain Publishing & Printing Proofreading

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www.lilobase.me DDD is all about Context @lilobase

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From Problem to Solution Business Domain & Architecture alignment Authoring Plateform Publishing & Printing Inventory Management Shipping Payment Processor Catalogue Invoicing Order Processing problem solution Payment processor Invoicing Order Processing Shipping Authoring Plateforme Inventory Management Catalogue Publishing Proofreading Proofreading Inventory E-commerce platform Authoring Publishing

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Domains & Subdomains Development Strategy Supporting Subdomain In-House development with external support if possible Generic Subdomain Outsourcing is an option Core (sub)Domain In-House development with Your best teams Key differentiator

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Domains & Subdomains Development Strategy Supporting Subdomain Customized Off The Shelf Software is an option Generic Subdomain Try to ﬁnd Off The Shelf solution Cost saving opportunities Core (sub)Domain Custom-made software High Cost & Quality Key differentiator

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From Problem to Solution Business Domain & Architecture alignment Authoring Plateform Publishing & Printing Inventory Management Shipping Payment Processor Catalogue Invoicing Order Processing problem solution Proofreading Inventory E-commerce platform Authoring Authoring Plateforme Publishing Catalogue Publishing Proofreading

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From Problem to Solution Business Domain & Architecture alignment Inventory E-commerce platform Authoring Authoring Plateforme Publishing Catalogue Publishing Proofreading These are your bounded contexts

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P Authoring Publishing E-commerce Stripe ShipMonk Shopify Context Mapping Relationship Hierarchy These are your bounded contexts OHS OHS ACL OHS C/S

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Authoring Publishing E-commerce Specific Architecture style You don’t need one architectural style Beware of the CRUD ES CQRS CRUD ? Stripe ShipMonk Shopify

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Stripe Still no microservices Bounded Context ≠ Deployment units ShipMonk Authoring Publishing E-commerce Shopify Deployment Unit

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Deployment Unit Stripe Still no microservices Bounded Context ≠ Deployment units ShipMonk Authoring Publishing E-commerce Shopify Deployment Unit

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Domains are not immutable Understanding is a never-ending process Stripe ShipMonk Authoring Publishing E-commerce Shopify Printing

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www.lilobase.me DDD is all about Boundaries @lilobase

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Semantic Boundaries Between BC meaning are different Authoring Publishing Book Chapter Chapter They are not the same book What happens if the author revises his book?

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Semantic Boundaries Between BC meaning are different Chapter This is why you must start by understand strategically your domain Author Book Reviews Release Catalogue

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Semantic Boundaries Between BC meaning are different Authoring Publishing Book Chapter Chapter Book Chapter Chapter Inside a Bounded Context, Don’t Repeat Yourself Between Bounded Context, Write Everything Twice

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Don’t cross them Between BC meaning are different Authoring Publishing Author Reviews Author Book Book Release Never create relationships between entities from two BC

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Don’t cross them Between BC meaning are different Authoring Publishing Book Book Release Author Author Reviews This is exactly the same

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Don’t cross them Between BC meaning are different Authoring Publishing Book Book Release Author Author Reviews API API

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Same for Events Between BC meaning are different Authoring Publishing This is exactly the same Event Bus Book Book Release Author Author Reviews

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Same for Events Between BC meaning are different Authoring Publishing Event Bus Book Book Release Author Author Reviews Translator Translator

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Transactional Boundaries Protect your integrity Authoring Book Chapter Chapter Chapter Statistics Inside your bounded Context live Entities They are grouped in Aggregates

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Transactional Boundaries Protect your integrity Book Chapter Chapter Chapter Statistics They are retrieved and persisted as a whole Inside an aggregate, Entities share the same lifecycle

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Transactional Boundaries Protect your integrity Book Chapter Chapter Chapter Statistics Who ensures the aggregate integrity All interactions are done through the Aggregate Root Write a new chapter

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Transactional Boundaries Protect your integrity Book Chapter Chapter Chapter Statistics Write a new chapter Chapter Inconsistency

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Transactional Boundaries Protect your integrity Book Chapter Chapter Chapter Statistics But don’t put to much in it Author What happens if we delete the book ? They must share the same lifecycle

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Transactional Boundaries Protect your integrity Book Chapter Chapter Chapter Statistics Author reference Author Id

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Designing Boundaries Protect your domain Printing Team We need printing margin Book Chapter Chapter Chapter Release We need the colorimetric proﬁle Printing margin Colorimetric proﬁle API Publishing Team

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Designing Boundaries Protect your domain API We need printing margin Book Chapter Chapter Chapter Release We need the colorimetric proﬁle Printing margin Colorimetric proﬁle Domain Leakage Publishing Team Printing Team

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Designing Boundaries Protect your domain Publishing Team Printing Team Publishing API We need printing margin Book We need the colorimetric proﬁle Printing margin Colorimetric proﬁle Printing API We discovered the need for an ACL

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www.lilobase.me DDD is all about Compassion @lilobase

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A A A Ubiquitous language Stakeholders & Team Alignement Dev Domain Expert Dev

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A A A not « just » a glossary Ubiquitous language Stakeholders & Team Alignement Dev Domain Expert Dev

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Ubiquitous language Each BC has its own Authoring Publishing A A

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Ubiquitous language Each BC has its own Authoring Publishing A A A A It is a common cause of miscommunication

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Pair Programing The best way to share a domain understanding Dev Domain Expert

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Know your users They might not be who you think they are Dev Domain Expert Product Owner Customer User

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Know your users They might not be who you think they are Dev Domain Expert Product Owner Customer User He has the last word regarding domain implementation

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Know your users They might not be who you think they are Dev Domain Expert Product Owner Customer User Prioritize development & formalize users’ feedback

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Know your users They might not be who you think they are Dev Domain Expert Product Owner Customer User Power of Life and Death over the project

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Know your users They might not be who you think they are Dev Domain Expert Product Owner Customer User Too often forgotten

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Know your users They might not be who you think they are Dev Domain Expert Product Owner Customer User Maybe you could spend a day per month working with them ?

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Know your users They might not be who you think they are Dev Domain Expert Product Owner Customer User They design the software speciﬁcation

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Know your users They might not be who you think they are Dev Domain Expert Product Owner Customer User What he understood goes into production

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“A loosely coupled software architecture and org structure to match” is a key predictor of: • Continuous Delivery Performance • Ability to scale organization and increase performance linearly This is what DDD is All About ! — Michael Plöd (@bitboss)

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www.lilobase.me Thanks @lilobase https://roti.express/r/ddd-hyf lgo.group