This Spring Boot/JPA application illustrates how to use the Saga and CQRS patterns in a microservice architecture.

1. @crichardson
About the Eventuate Tram
Customers and Orders example
Chris Richardson
Founder of Eventuate.io
Founder of the original CloudFoundry.com
Author of POJOs in Action
@crichardson
chris@chrisrichardson.net
http://microservices.io
http://eventuate.io
Copyright © 2020. Chris Richardson Consulting, Inc. All rights reserved

2. @crichardson
About the example
Demonstrates two key patterns:
Sagas - implement transactions that span services, https://
microservices.io/patterns/data/saga.html
CQRS - implement queries that retrieve data from multiple
services, https://microservices.io/patterns/data/cqrs.html
Built using Spring Boot, JPA and the Eventuate Tram
framework
https://github.com/eventuate-tram/eventuate-tram-examples-customers-and-orders/
Note: this presentation describes the development branch , which
reorganized/renamed the service modules.
These changes will soon be merged into master

3. @crichardson
System operations
CustomersAndOrdersApplication
≪commands≫
createCustomer(name, creditLimit)
createOrder(customerId, orderTotal)
cancelOrder(orderID)
≪queries≫
findOrder(orderId)
findOrderHistory(customerId)

4. @crichardson
Services

5. @crichardson
Customer Service - canvas

6. @crichardson
Customer Service - domain
model

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Order Service - canvas

8. @crichardson
Order Service - domain model

9. @crichardson
Order History Service - canvas

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Technical architecture
Service:
REST endpoint
Pub/sub events
Relational database - MySQL database
Message broker
Eventuate CDC - implements the Transaction Outbox pattern

11. @crichardson

12. @crichardson
Why all these events!?

13. @crichardson
Using the Saga pattern
Customer has a credit limit
createOrder()
Creates Order
Reserves credit
cancelOrder()
Updates Order
Releases credit
Event-driven
a.k.a
Choreography-based sagas
https://microservices.io/patterns/data/saga.html

14. Using the CQRS pattern
findOrderHistory()
Returns customers and
their orders
Order History Service
uses events to maintain a
replica in MongoDB
https://microservices.io/patterns/data/cqrs.html

15. @crichardson
Customer Service
Customer
Controller
Message
Producer
createCustomer()
Customer* Events
Order
Event
Consumer
Order* events
Customer
Database
≪entity≫
Customer
Customer
Repository
≪service≫
Customer
Service
Domain
Event
Publisher
POST /customers

16. Customer Service - code
customer-service-api-
messaging - events
published by the service
customer-service-api-web
- DTOs for REST
resources
customer-service - service
implementation

17. @crichardson
Order Service
Order Controller
Message
Producer
createOrder()
cancelOrder()
Order* Events
Customer
Event
Consumer
Customer* events
Order
Database
≪entity≫
Order
Order
Repository
≪service≫
Order
Service
Domain
Event
Publisher
POST /customers

18. Order Service - code
order-service-api-
messaging - events
published by the service
order-service-api-web -
DTOs for REST requests
and responses
order-service - service
implementation

19. @crichardson
Order History Service
CustomerOrder
HistoryController
findOrderHistory()
Order
History
Event
Consumer
Order* events
Order
History
Databas
CustomerView
Repository
≪service≫Ord
erHistory
ViewService
POST /customers
Customer* events

20. Order History Service - code
order-history-service-api-
web - DTOs for REST
requests and responses
order-service - service
implementation

21. @crichardson
Using the Saga pattern
https://microservices.io/patterns/data/saga.html

22. @crichardson
createOrder() sequence
diagram

23. @crichardson
cancelOrder() sequence
diagram

24. @crichardson
Using the CQRS pattern
https://microservices.io/patterns/data/cqrs.html

25. @crichardson
Implementing findOrderHistory()

26. @crichardson
@crichardson chris@chrisrichardson.net
http://eventuate.io
Questions?