CQRS and ES with Lagom
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This document discusses CQRS and event sourcing concepts and provides an introduction to the Lagom microservices framework. CQRS separates read and write operations by having separate models for each. Event sourcing stores an entity's state changes as a sequence of events. Lagom is a framework that uses CQRS and event sourcing principles and is built on reactive technologies like Akka. It aims to make microservices development productive and provides tools for persistence, querying and communication between services. The document includes code examples of using Lagom for CQRS and event sourcing.
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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