AxonIQCon22 - Beyond DDD 101 - Zambrovski-Galinski.pptx
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This document is a practice report on building multi-bounded context applications using Domain-Driven Design (DDD) and Command Query Responsibility Segregation/Event Sourcing (CQRS/ES) principles, authored by Jan Galinski and Simon Zambrovski. It outlines the foundational theories of DDD, patterns, and the use of the Axon Framework for system architecture, emphasizing strategic design, context mapping, and the separation of command and query models. Key takeaways include the importance of starting with a modulith, evolving system design, and leveraging the Axon Framework for building scalable applications.
AxonIQCon22 - Beyond DDD 101 - Zambrovski-Galinski.pptx
- 1. Beyond DDD 101 A practice report on building multi bounded context CQRS/ES applications Jan Galinski & Simon Zambrovski Amsterdam, 23.09.2022 1
- 2. Who we are Jan Galinski Simon Zambrovski 23.09.2022, AxonIQCon 2022 2 Consultants @ holisticon Backend developers, software architects DDD, CQRS/ES, Axon Framework, Spring, Kotlin, Java
- 3. What is Holisticon • IT Consulting • Hamburg, Hannover, Kiel • Cool crew • Best Employer 2022 in Hamburg • We are hiring! 23.09.2022, AxonIQCon 2022 3 BESTE BERATUNG – BESTE SOFTWARE
- 4. Motivation • We love architecture • DDD • CQRS • Event Sourcing • Large-scale applications running on JVM • We love Axon Framework • We want to share our experience 23.09.2022, AxonIQCon 2022 4 https://www.pexels.com/de-de/foto/verschiedene-puzzlespiele-1586951/
- 5. Foundation – Theory - DDD • Set of principles for system implementation • Requirement Engineering • Domain Modeling • Strategic Design • Bounded Context identification • Context Mapping • Design • Ubiquitous Language • Design Patterns 23.09.2022, AxonIQCon 2022 5 https://www.amazon.com/Domain-Driven-Design-Tackling-Complexity-Software/dp/0321125215
- 6. Foundation – Theory – DDD Patterns • Modeling of Bounded Context relationships (for Microservices) • Separate Ways • Upstream/Downstream • Open Host Service + Published Language • Anti Corruption Layer • Tactical Design • Value Object, Entity, Aggregate, Aggregate Root • Domain Service, Factory, Repository • Domain Event • Saga Pattern 23.09.2022, AxonIQCon 2022 6
- 7. Foundation – Theory – CQRS/ES • Command Query Responsibility Segregation Pattern • Reduce complexity of Domain model • Separate Command model from Query model (optimized) • Scale-out independently • Event Sourcing Persistence Strategy • Store Domain Events (versus store State) • Derive State from Domain Event stream • CQRS/ES • Use Domain Events to communicate between Command and Query models • Allow late stream consumption (stream replay) 23.09.2022, AxonIQCon 2022 7
- 8. Domain Foundation - Onion Architecture Driving (primary) Adapter Driven (secondary) Adapter Domain Model Ring Port Port Application Service Ring Infrastructure Ring 23.09.2022, AxonIQCon 2022 8
- 9. Axon Framework 101 • FOSS framework in Java for building DDD CQRS(/ES) systems • Explicit message concept • 3 buses for decoupling • Command -> Addressed intent of a change, may fail, unicast • Event -> Fact, broadcast • Query -> Request for data, has result, multicast • Domain Model Segregation (implements CQRS) • Event Sourcing implementation (different Event Stores) • Separation of business logic from configuration 23.09.2022, AxonIQCon 2022 9 https://developer.axoniq.io/download
- 10. Possible Architecture using Axon Framework 23.09.2022, AxonIQCon 2022 10 https://docs.axoniq.io/reference-guide/
- 11. System evolution in single context • Build components using buses for communication • Start with modulith • Distribute along buses • Scale out projections • Build new projections later • Change infrastructure 23.09.2022, AxonIQCon 2022 11
- 12. Domain Core Onion Architecture with Axon Framework REST Adapter Query Model Command Model Command Gateway Query Gateway Projection Repository Aggregate Repository Query Bus Comma nd Bus Event Bus Pivotal Event Bus Pivotal Event Bus Domain Event Bus Domain Comma nd Bus Query Bus Saga 23.09.2022, AxonIQCon 2022 12
- 13. 23.09.2022, AxonIQCon 2022 13 https://www.pexels.com/de-de/foto/mann-frustration-kopfschmerzen-brille-9843268/
- 14. Domain Core Onion Architecture with Axon Framework REST Adapter Query Model Command Model Command Gateway Query Gateway Projection Repository Aggregate Repository Query Bus Comma nd Bus Event Bus Pivotal Event Bus Pivotal Event Bus Domain Event Bus Domain Comma nd Bus Query Bus Saga 23.09.2022, AxonIQCon 2022 14
- 15. Simplified context building block Query Model Command Model Query Bus Comma nd Bus Event Bus Event Bus Comma nd Bus Query Bus Saga 23.09.2022, AxonIQCon 2022 15
- 16. Patterns 23.09.2022, AxonIQCon 2022 16 Q S C ? Q S C
- 17. Q Master Data Query Q S D U 23.09.2022, AxonIQCon 2022 17 „You know some things that I need to know, please tell me!“ Query
- 18. Master Data Query Q S Q D U 23.09.2022, AxonIQCon 2022 18 Query Benefits • Simple (~ GET) • No redundancy (GDPR) • Encapsulate complex business logic Challenges • Runtime dependency • Trap: Building specialized projections for other teams • Outdated data, caching
- 19. Trigger a query C U D 23.09.2022, AxonIQCon 2022 19 Q Q „I made some changes … ask me if you want more details.“ Query C‘
- 20. Trigger a query C U D 23.09.2022, AxonIQCon 2022 20 Q Q Query Benefits •„Cache invalidation“ Challenges •Runtime dependency* •Load (query avalanche)
- 21. Query Aggregator C Q U D 23.09.2022, AxonIQCon 2022 21 „Here is some data that could be useful to build your projection.“ Query Q‘ C‘
- 22. Query Aggregator C Q U D 23.09.2022, AxonIQCon 2022 22 Query Benefits • Decoupling • Build complex projections from other contexts Challenges • Event Payload definition • Payload interpretation
- 23. Reacting to Fact C S C U D 23.09.2022, AxonIQCon 2022 23 Command „I changed some things … deal with it.“ C‘ C‘
- 24. Reacting to Fact C S C U D 23.09.2022, AxonIQCon 2022 24 Command Benefits • Simple • Decoupled • Event Driven Challenges • Downstream Command model must follow • Command-Event-Command bridge
- 25. Downstream Saga C S C D U 23.09.2022, AxonIQCon 2022 25 Command „I need you to do something for me, and I need the result.“ C* C‘ C‘
- 26. Downstream Saga C S C D U 23.09.2022, AxonIQCon 2022 26 Command Benefits • Build for failure • Delegate sub processes Challenges • Compensation • Complex for more than one context
- 27. External Orchestrator C S C D U U 23.09.2022, AxonIQCon 2022 27 Command C* C* C‘ C‘ „If you two cannot handle it, let me take control.“
- 28. External Orchestrator C S C D U U 23.09.2022, AxonIQCon 2022 28 Command Benefits • Build for failure • Separate ways • Business process Challenges • Compensation • Complex for more than one context
- 29. Key Takeaways • Domain Driven Design • Start with Strategic Design • Do proper Context Mapping – Relationships! • CQRS/ES • Use Command / Event / Query abstractions („Events only“ is not enough) • Use Axon Framework if working on JVM • Practical • Start with a modulith • Build evolutionary • Distribute on demand 23.09.2022, AxonIQCon 2022 29
- 30. Thank you... Questions? • Holisticon AG • https://holisticon.de/ • Jan • https://about.me/jangalinski • Simon • https://about.me/zambrovski • Axon Framework • https://developer.axoniq.io/ 23.09.2022, AxonIQCon 2022 30 https://www.pexels.com/de-de/foto/fragezeichen-auf-zerknittertem-papier-5428826/
Editor's Notes
- #3: Camunda Champions/Process Automation
- #7: Context defines semantics ACL - semantical mapping Design:
- #8: Command Model: validation Query Model: optimized projections
- #10: ES: EventStore(s), Replay, Snapshotting, Upcasting
- #14: This was a lot to swallow – DD/CQR/Oninon in 10 Minutes Reached the Plateau of maximum complexity Story of ranked Break down
- #15: we only care about the external/pivotal view
- #16: 2 models, a saga, 3 busses
- #17: Separate ways is already a pattern not invented but recognized/discovered Introduce a model for context communication how they commincate: patterns – no true or false, combinations are possible We have 6 today, but there might be more Query Patterns Command Patterns
- #18: Reporting collects customer data and account to send out letters credit manager needs balance history to calculate interest rates ...
- #19: Hint: GraphQL Remote projection
- #21: Event: Milestone/Trigger/Notification Runtime: not that hard Query might not return the result the event intended
- #22: Event: Fat Event, contains data
- #23: Do we event source fat pivotal events? next: command
- #25: ACL Pure Choreography
- #26: customer wants to cancel releationship account management discovers open debt and rejects if sync: command failing might be enough if async: ack/nack event
- #27: pure orchestration
- #28: Separate ways Complex business scenarios Process engine