[SpringOne2016] Developing Microservices with Aggregates

SpringOne Platform 2016報告会

Transcript

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   "QQMJDBUJPOT Acroquest Technology Co., LTD.
 Shin Tanimoto (@cero_t)
5. ͡Όͳͯ͘
6. @crichardson Developing Microservices with Aggregates Chris Richardson Founder of Eventuate.io Founder of the original CloudFoundry.com Author of POJOs in Action @crichardson chris@chrisrichardson.net http://eventuate.io
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11. @crichardson Microservice architecture Browser Mobile Device Store Front UI API Gateway Catalog Service Review Service Order Service … Service Catalog Database Review Database Order Database … Database HTML REST REST Apply X-axis and Z-axis scaling to each service independently
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13. @crichardson Product service Customer service Order service Domain model = tangled web of classes Order OrderLine Item quantity … Address street city … Customer Product name price ? ? creditLimit
14. @crichardson But it violates encapsulation… BEGIN TRANSACTION … SELECT ORDER_TOTAL FROM ORDERS WHERE CUSTOMER_ID = ? … SELECT CREDIT_LIMIT FROM CUSTOMERS WHERE CUSTOMER_ID = ? … INSERT INTO ORDERS … … COMMIT TRANSACTION Private to the Order Service Private to the Customer Service
15. @crichardson 2PC is not a viable option Guarantees consistency BUT 2PC is best avoided Not supported by many NoSQL databases etc. CAP theorem 㱺 2PC impacts availability ….
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19. @crichardson 2PC is not a viable option Guarantees consistency BUT 2PC is best avoided Not supported by many NoSQL databases etc. CAP theorem 㱺 2PC impacts availability ….
20. @crichardson Aggregate rule #2 Transaction = processing one command by one aggregate
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22. @crichardson Aggregate granularity If an update must be atomic then it must be handled by a single aggregate Therefore Aggregate granularity is important
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24. @crichardson Aggregate granularity Consistency Scalability/ User experience Customer Order Product Customer Order Product Customer Order Product
25. ͔ͩΒɺͲ͏͢Δͷʁ
26. @crichardson Customer management How to maintain data consistency between aggregates? Order management Order Service placeOrder() Customer Service updateCreditLimit() Customer creditLimit ... has orders belongs to Order total Invariant: sum(open order.total) <= customer.creditLimit ?
27. @crichardson Use event-driven, eventually consistent order processing Order Service Customer Service Order created Credit Reserved Credit Check Failed Create Order OR Customer creditLimit creditReservations ... Order state total … create() reserveCredit() approve()/reject()
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32. @crichardson How atomically update database and publish an event Order Service Order Database Message Broker insert Order publish OrderCreatedEvent dual write problem ?
33. @crichardson 2PC is not an option
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35. @crichardson Event sourcing = event-centric persistence Application Database Event store update publish X
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37. @crichardson Persists events
    NOT current state Event table Entity type Event id Entity id Event data Order 902 101 … OrderApproved Order 903 101 … OrderShipped Event type Order 901 101 … OrderCreated
38. @crichardson The present is a fold over history currentState = foldl(applyEvent, initialState, events)
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59. @crichardson Request handling in an event sourced application HTTP Handler Event Store pastEvents = findEvents(entityId) Order new() applyEvents(pastEvents) newEvents = processCmd(someCmd) saveEvents(newEvents) (optimistic locking) Order Service applyEvents(newEvents)
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61. @crichardson Event Store publishes events consumed by other services Event Store Event Subscriber subscribe(EventTypes) publish(event) publish(event) Customer update() Customer Service
62. @crichardson Event Store publishes events consumed by other services Event Store Event Subscriber subscribe(EventTypes) publish(event) publish(event) CQRS View update() Service Xyz send notifications …
63. @crichardson The Customer aggregate Money creditLimit Map<OrderId, Money> creditReservations Customer List<Event> process(CreateCustomerCommand cmd) { … } List<Event> process(ReserveCreditCommand cmd) { … } … void apply(CustomerCreatedEvent anEvent) { … } void apply(CreditReservedEvent anEvent) { … } … State Behavior
64. @crichardson Familiar concepts restructured class Customer { public void reserveCredit( orderId : String, amount : Money) { // verify // update state this.xyz = … } public List<Event> process( ReserveCreditCommand cmd) { // verify … return singletonList( new CreditReservedEvent(…); ) } public void apply( CreditReservedEvent event) { // update state this.xyz = event.xyz }
65. @crichardson Customer command processing
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