When Microservices met Event Sourcing

Talk presented at the O'Reilly Software Architecture Conference 2017 https://conferences.oreilly.com/software-architecture/sa-ny/public/schedule/detail/56806

Transcript

1. When Microservices met Event Sourcing Vinicius Gomes
2. Vinicius Gomes ! Software developer at ThoughtWorks ! vvgomes.com/blog ! twitter.com/vvgomes
3. Agenda ! The Traditional Approach ! Introduction to Event Sourcing ! Command Query Responsibility Segregation ! Implementing the "Event Sourced Microservices" Architecture
4. The Traditional Approach
5. Example: Online Restaurant
6. Online Restaurant
7. Online Restaurant ! Open an order
8. Online Restaurant ! Add Menu Item
9. Benefits ! Simple ! HTTP ! Technology agnostic
10. Challenges ! Coupling
11. Challenges ! Coupling ! Resilience
12. Challenges ! Coupling ! Resilience ! Response time
13. Challenges ! Coupling ! Resilience ! Response time ! User intent POST /orders/8659a0d6/items/ “Add item to order”
14. Challenges ! Coupling ! Resilience ! Response time ! User intent ! Current / mutable state
15. Event Sourcing
16. Domain Events ! Model the past ! Immutable ! Immortal
17. Event Store ! Append only ! Sequential ! History
18. Aggregates ! Applying events
19. Aggregates ! Applying events
20. Aggregates ! Applying events
21. Aggregates ! Applying events
22. Aggregates ! Applying events
23. Aggregates ! Applying events
24. Aggregates ! Applying events
25. Commands ! Represent user intent ! Cause new events
26. Commands ! Commands are more meaningful than HTTP methods POST /orders/8659a0d6/items/ AddItemToOrderCommand as opposed to
27. Commands How do clients send commands?
28. Commands ! A collection resource that accepts multiple commands POST /orders/8659a0d6/commands/
29. Commands ! Command URI POST /orders/8659a0d6/orderItems/commands/add
30. Commands
31. Commands
32. Commands Queries?
33. Queries ! Event Store is not good for queries ! Most applications ! A few writes ! A lot of reads
34. Command Query Responsibility Segregation
35. CQRS
36. CQRS
37. CQRS ! Command Model ! Commands definitions ! Events definitions ! The aggregate ! Aggregate repository ! Write only API ! Query Model ! Event listeners ! Query entities ! Repositories ! Read only API
38. Sample Implementation
39. Example: Online Restaurant
40. Example: Online Restaurant
41. Example: Online Restaurant
42. Example: Online Restaurant
43. Technologies ! Java 8 ! Spring Boot ! Axon Framework ! Spring Data REST ! RabbitMQ
44. Conclusions
45. Microservices + Event Sourcing ! Benefits
46. Microservices + Event Sourcing ! Benefits ! History based queries
47. Microservices + Event Sourcing ! Benefits ! History based queries ! Audit log by design
48. Microservices + Event Sourcing ! Benefits ! History based queries ! Audit log by design ! Immutability
49. Microservices + Event Sourcing ! Benefits ! History based queries ! Audit log by design ! Immutability ! User intent
50. Microservices + Event Sourcing ! Benefits ! History based queries ! Audit log by design ! Immutability ! User intent ! Decoupling
51. Microservices + Event Sourcing ! Benefits ! History based queries ! Audit log by design ! Immutability ! User intent ! Decoupling ! Resilience
52. Microservices + Event Sourcing ! Benefits ! History based queries ! Audit log by design ! Immutability ! User intent ! Decoupling ! Resilience ! Challenges
53. Microservices + Event Sourcing ! Benefits ! History based queries ! Audit log by design ! Immutability ! User intent ! Decoupling ! Resilience ! Challenges ! Complexity ! Snapshots
54. Microservices + Event Sourcing ! Benefits ! History based queries ! Audit log by design ! Immutability ! User intent ! Decoupling ! Resilience ! Challenges ! Complexity ! Snapshots ! Upcasting
55. Microservices + Event Sourcing ! Benefits ! History based queries ! Audit log by design ! Immutability ! User intent ! Decoupling ! Resilience ! Challenges ! Complexity ! Snapshots ! Upcasting ! Race conditions
56. Microservices + Event Sourcing ! Benefits ! History based queries ! Audit log by design ! Immutability ! User intent ! Decoupling ! Resilience ! Challenges ! Complexity ! Snapshots ! Upcasting ! Race conditions ! Event contracts
57. Microservices + Event Sourcing ! Benefits ! History based queries ! Audit log by design ! Immutability ! User intent ! Decoupling ! Resilience ! Challenges ! Complexity ! Snapshots ! Upcasting ! Race conditions ! Event contracts ! Eventual consistency
58. When Microservices met Event Sourcing Vinicius Gomes