When Microservices Meet Event Sourcing

Presented at:
* ThoughtWorks Tech Talks NYC Meetup on May 2017
* Developer Week Conference NYC on Jun 2017

Transcript

1. WHEN MICROSERVICES MEET EVENT SOURCING Vinicius Gomes 1
2. VINICIUS GOMES Software developer at ThoughtWorks vvgomes.com/blog twitter.com/vvgomes 2
3. AGENDA The Traditional Approach Introduction to Event Sourcing CQRS Demo Summary 3
4. THE TRADITIONAL APPROACH 4
5. EXAMPLE Online Restaurant 5
6. ONLINE RESTAURANT Data Model 6
7. ONLINE RESTAURANT Services 7
8. Restaurant ONLINE RESTAURANT 8 POST GET I want to open an order! 200 ✔
9. Restaurant ONLINE RESTAURANT 9 POST GET I want to add an item to my order! 200 ✔
10. THE TRADITIONAL APPROACH • Simple to implement • Technology agnostic 10 GET POST PUT DELETE
11. CHALLENGES 11
12. CHALLENGES Coupling 12
13. CHALLENGES Coupling Resilience 13 Restaurant POST GET I want to add an item to my order! 503
14. CHALLENGES Coupling Resilience Response time 14
15. CHALLENGES Coupling Resilience Response time User intent 15 POST /orders/8659a0d6/items/ Add item to order
16. CHALLENGES Coupling Resilience Response time User intent Current / mutable state 16 { "id": “6a208c41…”, "status": "OPEN", "items": [ { "id": “be596c8e…”, "quantity": 1 }, { "id": “5d09509c…”, "quantity": 2 }, { "id": “cc52d1b6…”, "quantity": 1 } ] }
17. EVENT SOURCING 17
18. EVENT SOURCING 18
19. DOMAIN EVENTS 19 { "payload": { "orderId": “be596c8e…”, "itemId": “5d09509c…”, "quantity": 1 }, "payloadType": “com.restaurant.ItemAddedToOrderEvent”, "timestamp": “2017-03-25 08:48:51 -03:00”, "revision": “2”, "aggregateId": “6a208c41…” } Model the past Immutable Permanent
20. EVENT STORE Append only Sequential Long-lived 20
21. AGGREGATES 21 state = reduce(handle, {}, events) Reducer function Reducing events into state
22. AGGREGATES Example 22 { }
23. AGGREGATES Example 23 payload: { id: “42” } { "id": “42”, "status": "OPEN", "items": [ ] }
24. AGGREGATES Example 24 { "id": “42”, "status": "OPEN", "items": [ { "id": “43”, “quantity": 1 } ] } payload: { orderId: “42”, itemId: “43”, quantity: 1 }
25. payload: { orderId: “42”, itemId: “44”, quantity: 2 } AGGREGATES Example 25 { "id": “42”, "status": "OPEN", "items": [ { "id": “43”, “quantity": 1 }, { "id": “44”, “quantity": 2 } ] }
26. AGGREGATES Example 26 { "id": “42”, "status": "OPEN", "items": [ { "id": “44”, “quantity": 2 } ] } payload: { orderId: “42”, itemId: “43” }
27. AGGREGATES Example 27 { "id": “42”, "status": "PLACED", "items": [ { "id": “44”, “quantity": 2 } ] } payload: { orderId: “42” }
28. AGGREGATES Example 28 { "id": “42”, "status": "PLACED", "items": [ { "id": “44”, “quantity": 2 } ] } Order Aggregate
29. COMMANDS 29 Add item to order { "type": “com.restaurant.AddItemToOrderCommand”, "payload": { "orderId": “be596c8e…”, "itemId": “5d09509c…”, "quantity": 1 }, "timestamp": “2017-03-25 08:48:51 -03:00” }
30. COMMANDS 30 (state, command) -> [event] Handling a command
31. COMMANDS 31 How do clients send commands? I want to add an item to my order! ?
32. COMMANDS 32 Reviewing REST Resource Collection host/api/orders
33. COMMANDS 33 Reviewing REST Resource host/api/orders/8659a0d6
34. COMMANDS 34 Reviewing REST Nested Resource host/api/orders/8659a0d6/items/5d1a8457
35. COMMANDS 35 Reviewing REST HTTP Methods GET POST PUT/PATCH DELETE
36. COMMANDS 36 Reviewing REST Hypermedia Formats
37. COMMANDS 37 Commands can be resources
38. COMMANDS Option #1 Generic “Commands” nested-resource 38 POST /orders/8659a0d6/commands { “type": “AddItemToOrderCommand”, "menuItem": “/menu/items/8d30d99“, “quantity": 2 }
39. COMMANDS Option #2 Command URI 39 POST /orders/8659a0d6/items/commands/add { "menuItem": “/menu/items/8d30d99“, “quantity": 2 }
40. COMMANDS Command discoverability 40
41. EVENT SOURCING 41
42. 42 Queries?
43. QUERIES Bad news The Event Store is not good for queries 43 Most applications •A few writes •A lot of reads
44. CQRS 44
45. CQRS Command Query Responsibility Segregation 45 Write ✍ Read
46. Service CQRS 46 Command Query Publish Listen
47. Service A CQRS 47 Service B
48. CQRS 48 Command model •Command definitions •Event definitions •The aggregate •Aggregate repository •Write only API Query model •Event listeners •Query entities •Repositories •Read only API
49. DEMO 49
50. DEMO Online Restaurant 50 Service
51. DEMO Online Restaurant 51
52. EXAMPLE: ONLINE RESTAURANT 52 Online Restaurant Publishes Listen to
53. EXAMPLE: ONLINE RESTAURANT 53 Online Restaurant Publishes Listen to Publishes Listen to
54. TECHNOLOGIES Java Spring Boot Axon Framework Spring Data REST RabbitMQ 54 https://github.com/vvgomes/event-driven-restaurant
55. SUMMARY 55
56. MICROSERVICES + EVENT SOURCING Benefits •History based queries •Audit log by design •Immutability •User intent •Decoupling •Resilience 56 Challenges •Complexity •Snapshots •Upcasting •Race conditions •Event contracts •Eventual consistency
57. WHEN MICROSERVICES MEET EVENT SOURCING Vinicius Gomes 57