WHEN MICROSERVICES MEET EVENT SOURCING Vinicius Gomes 1 - PowerPoint PPT Presentation

WHEN MICROSERVICES MEET EVENT SOURCING Vinicius Gomes 1

VINICIUS GOMES Software developer at ThoughtWorks vvgomes.com/blog twitter.com/vvgomes 2

AGENDA The Traditional Approach Introduction to Event Sourcing CQRS Demo Summary 3

THE TRADITIONAL APPROACH 4

EXAMPLE Online Restaurant 5

ONLINE RESTAURANT Data Model 6

ONLINE RESTAURANT Services 7

ONLINE RESTAURANT Restaurant I want to open an order ! POST 📲 G E T 200 ✔ 8

ONLINE RESTAURANT Restaurant I want to add an item to my order! GET POST 📲 200 ✔ 9

THE TRADITIONAL APPROACH • Simple to implement • Technology agnostic GET POST PUT DELETE 10

CHALLENGES 11

CHALLENGES Coupling 12

CHALLENGES Coupling Resilience Restaurant I want to add an item to my order! GET POST 📲 503 👏 13

CHALLENGES Coupling Resilience Response time 14

CHALLENGES Coupling Resilience Add item to order Response time User intent POST /orders/8659a0d6/items/ 15

CHALLENGES Coupling Resilience { "id": “6a208c41…”, Response time "status": "OPEN", "items": [ { User intent "id": “be596c8e…”, "quantity": 1 Current / mutable state }, { "id": “5d09509c…”, "quantity": 2 }, { "id": “cc52d1b6…”, "quantity": 1 } ] } 16

EVENT SOURCING 17

EVENT SOURCING 18

DOMAIN EVENTS Model the past Immutable Permanent { "payload": { "orderId": “be596c8e…”, "itemId": “5d09509c…”, "quantity": 1 }, "payloadType": “com.restaurant.ItemAddedToOrderEvent”, "timestamp": “2017-03-25 08:48:51 -03:00”, "revision": “2”, "aggregateId": “6a208c41…” } 19

EVENT STORE Append only Sequential Long-lived 20

AGGREGATES Reducing events into state state = reduce(handle, {}, events) Reducer function 21

AGGREGATES Example { } 22

AGGREGATES Example { "id": “42”, "status": "OPEN", "items": [ ] } payload: { id: “42” } 23

AGGREGATES Example { "id": “42”, "status": "OPEN", "items": [ { "id": “43”, “quantity": 1 } ] } payload: { orderId: “42”, itemId: “43”, quantity: 1 } 24

AGGREGATES Example { "id": “42”, "status": "OPEN", "items": [ { "id": “43”, “quantity": 1 }, { "id": “44”, “quantity": 2 } ] } payload: { orderId: “42”, itemId: “44”, quantity: 2 } 25

AGGREGATES Example { "id": “42”, "status": "OPEN", "items": [ { "id": “44”, “quantity": 2 } ] } payload: { orderId: “42”, itemId: “43” } 26

AGGREGATES Example { "id": “42”, "status": "PLACED", "items": [ { "id": “44”, “quantity": 2 } ] } payload: { orderId: “42” } 27

AGGREGATES Example Order Aggregate { "id": “42”, "status": "PLACED", "items": [ { "id": “44”, “quantity": 2 } ] } 28

COMMANDS Add item to order { "type": “com.restaurant. AddItemToOrderCommand ”, "payload": { "orderId": “be596c8e…”, "itemId": “5d09509c…”, "quantity": 1 }, "timestamp": “2017-03-25 08:48:51 -03:00” } 29

COMMANDS Handling a command (state, command) -> [event] 30

COMMANDS How do clients send commands? I want to add an item to my order! ? 📲 31

COMMANDS Reviewing REST Resource Collection host/api/orders 32

COMMANDS Reviewing REST Resource host/api/orders/8659a0d6 33

COMMANDS Reviewing REST Nested Resource host/api/orders/8659a0d6/items/5d1a8457 34

COMMANDS Reviewing REST HTTP Methods GET POST PUT/PATCH DELETE 35

COMMANDS Reviewing REST Hypermedia Formats 36

COMMANDS Commands can be resources 37

COMMANDS Option #1 Generic “Commands” nested-resource POST /orders/8659a0d6/commands { “type": “AddItemToOrderCommand”, "menuItem": “/menu/items/8d30d99“, “quantity": 2 } 38

COMMANDS Option #2 Command URI POST /orders/8659a0d6/items/commands/add { "menuItem": “/menu/items/8d30d99“, “quantity": 2 } 39

COMMANDS Command discoverability 40

EVENT SOURCING 41

Queries? 42

QUERIES Bad news 😕 The Event Store is not good for queries Most applications •A few writes •A lot of reads 43

CQRS 44

CQRS C ommand Write ✍ Q uery Read 📗 R esponsibility S egregation 45

CQRS Service Publish Command 📲 Query n e t s i L 46

CQRS Service A Service B 47

CQRS Command model Query model •Command de fi nitions •Event listeners •Event de fi nitions •Query entities •The aggregate •Repositories •Aggregate repository •Read only API •Write only API 48

DEMO 49

DEMO Online Restaurant Service 50

DEMO Online Restaurant 51

EXAMPLE: ONLINE RESTAURANT Online Restaurant Listen to Publishes 52

EXAMPLE: ONLINE RESTAURANT Online Restaurant Listen to Publishes P u o t b n l e i s t s h i L e s 53

TECHNOLOGIES Java Spring Boot Axon Framework Spring Data REST RabbitMQ https://github.com/vvgomes/event-driven-restaurant 54

SUMMARY 55

MICROSERVICES + EVENT SOURCING Bene fi ts Challenges •History based queries •Complexity •Audit log by design •Snapshots •Immutability •Upcasting •User intent •Race conditions •Decoupling •Event contracts •Resilience •Eventual consistency 56

WHEN MICROSERVICES MEET EVENT SOURCING Vinicius Gomes 57