CQRS and ES with Lagom
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Presentation about the Lagom framework and the CQRS and Event Sourcing principles it is build upon.
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CQRS and ES with Lagom
- 1. 1 CQRS & EVENT SOURCING With Lagom
- 2. 2 . 1 Miel Donkers @mieldonkers github.com/mdonkers @codecentric_nl
- 3. 2 . 2 Agenda CQRS concepts Event Sourcing concepts Introduction Lagom framework CQRS & ES as basis for Lagom Lagom code / demo
- 4. 3 . 1 What is CQRS
- 5. 3 . 2 What is CQRS Command Query Responsibility Segregation
- 6. 3 . 3 Traditional Architecture © Martin Fowler
- 7. 3 . 4 CQRS Architecture © Martin Fowler
- 8. 3 . 5 Storing data Simple approach Single database Normalized tables for write-side data Views for denormalizing data Keep queries simple
- 9. 3 . 6 CQRS related to DDD DDD - Domain Driven Design Bounded Context Aggregate Command Event
- 10. 3 . 7 DDD example
- 11. 3 . 8 Command - Event - State
- 12. 3 . 9 Service owns data
- 13. 4 . 1 What is ES
- 14. 4 . 2 What is ES Event Sourcing Event describes the state change of aggregate Event is saved in event store Events can be replayed to re-create the current state.
- 15. 4 . 3 CQRS & ES Combined
- 16. 4 . 4 Architecture with Transactions © Microsoft - CQRS Journey
- 17. 4 . 5 Architecture with Messages © Microsoft - CQRS Journey
- 18. 4 . 6 The hard parts
- 19. 4 . 7 Consistency Key feature for the Event Store Without transactions, much work needed to make as reliable Versioning / timestamps Eventual consistency
- 20. 4 . 8 Error Handling Distinguish between business faults and errors. Errors can be re-tried. Business faults should have pre-determined reaction.
- 21. 4 . 9 Other disadvantages Many moving parts, makes it hard to debug the system as a whole CQRS not for every bounded context
- 23. 4 . 11 Advantages Auditing and historical tracing Read and write side can be optimized separately Debug in local environment Small components which are easy to update / fix No ORM impedance mismatch
- 24. 5 . 1 Lagom microservice framework
- 25. 5 . 2 Design philosophy Distributed Asynchronous Productivity
- 26. 5 . 3 Concepts Microservices Polyglot Design Driven APIs Immutability Event Sourcing and CQRS
- 27. 5 . 4 Opiniated ServiceCall<Source<String, NotUsed>, Source<String, NotUsed>> stream(); @Override default Descriptor descriptor() { return named("stream").withCalls(namedCall("stream", this::stream)) .withAutoAcl(true); }
- 28. 5 . 5 Core technologies Akka Akka Streams Akka Persistence Akka Cluster Play ConductR
- 29. 5 . 6 Lagom persistence Cassandra PersistentEntity Requires Command, Eventand State Single instance kept in memory
- 30. 5 . 7 Command - Event - State
- 32. 5 . 8 5 . 9 Get me all inspections with remarks for a given ship Query example
- 33. 5 . 10 Lagom JDBC support Available in 1.2 release Slick Storing and reading entities
- 34. 6 . 1 CODE
- 35. 6 . 27 . 1 Wrapping Up
- 36. 7 . 2 Lessons learned Conventions make setup easy Framework on top of many layers
- 37. ... [INFO] Service locator is running at http://localhost:8000 [INFO] Service gateway is running at http://localhost:9000 ... [INFO] (Service started, press enter to stop and go back to the console...) [error] c.l.l.i.s.ServiceRegistrationModule$RegisterWithServiceRegistry - Service name=[hello] couldn't register itself to the service locator. com.lightbend.lagom.javadsl.api.transport.TransportException: <head> ... [error] a.c.s.PersistentShardCoordinator - Persistence failure when replaying events for persistenceId [/sharding/HelloEntityCoordinator]. Last known sequence number [0] com.lightbend.lagom.javadsl.api.transport.PolicyViolation: <head> ...
- 38. 7 . 3 7 . 4 Links Martin Fowler - CQRS Microsoft - CQRS Journey Lagom Framework Miel Donkers - Lagom CQRS Demo
- 39. 7 . 5 Thank You!
- 40. 7 . 6 We're hiring