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OReilly SACON2018 - Events on the outside, on the inside, and at the core

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Chris Richardson Founder of Eventuate.io Founder of the original CloudFoundry.com Author of POJOs in Action and Microservices Patterns @crichardson [email protected] http://learn.microservices.io Events on the outside, on the inside and at the core
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Page 1: OReilly SACON2018 - Events on the outside, on the inside, and at the core

Chris Richardson

Founder of Eventuate.io Founder of the original CloudFoundry.com Author of POJOs in Action and Microservices Patterns

@crichardson [email protected] http://learn.microservices.io

Events on the outside, on the inside and at the core

Page 2: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

About Chris

http://learn.microservices.io ctwsoftarchconf18

Page 3: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

What’s an event?

Page 4: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

http://www.merriam-webster.com/dictionary/event

Page 5: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

Examples of events

Page 6: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

Events play a role at every level of an architecture

Page 7: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

Events on the outside E-commerce Application

Fulfilment Application

Page 8: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

An application emits an event when…

OrderCreated

E-commerce Application

OrderShipped InvoiceBecameOverdue

State changes Passage of time

Page 9: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

Who consumes an event?

Notification Service

Dashboard/ Monitoring

OrderCreated Email SMS …

E-commerce Application

Fulfilment Application

Page 10: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

Implements the Open for extension/Closed for

modification principle for applications

Legacy Application New Feature

Page 11: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

How to transport events?

Page 12: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

messaging system

Inside the firewall: Messaging-based IPC

Sender Recipientmessage

Channel

AWS Kinesis

Page 13: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

Outside the firewall

Page 14: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

Polling for events

HTTP Periodically poll for events

Atom Publishing Protocol (AtomPub) Based on HTTP Head is constantly changing Tail is immutable and can be efficiently cached

High-latency, inefficient

Page 15: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

Using WebSockets

Browser

Web Socket

STOMP

Client application

Service

Web Socket

STOMP

ApplicationSUBSCRIBE

MESSAGE

MESSAGE

Low latency, more efficient, but what about past events?

Page 16: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

Webhooks = web friendly publish/subscribe

Client Application

register(events, callbackUrl)

POST callbackUrl

POST callbackUrl

…

Low latency, more efficient, but what about past events?

Page 17: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

Events on the inside

E-commerce application

Order Service

Catalog Service

Page 18: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

The Microservice architecture enables the rapid, safe delivery of

large, complex applications

Page 19: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

E-commerce application - refactored to services

Order Service

Catalog Service

API

API

Customer Service

API

…. Service

API

But what about transactions and queries that span

services?

Private DBs

Page 20: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

How to implement transactions that span services?

Page 21: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

How to enforce the customer’s credit limit?

Customer

creditLimit ...

has ordersbelongs toOrder

total

Invariant: sum(open order.total) <= customer.creditLimit

?placeOrder()

Order Service

updateCreditLimit()

Customer Service

No 2PC

Page 22: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

Use event-driven, choreography-based sagas

Customer

creditLimit creditReservations ...

Order

total

placeOrder()Order Service Customer Service

create()

Order created

Credit Reserved

reserveCredit()

approve()

Page 23: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

How to implement queries that span services?

Page 24: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

Find new customers who have placed high value orders that have shipped

Page 25: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

Use Command Query Responsibility Segregation

Order Service

Customer Service

Message Broker

Customer *

Customer View

Service

Order *

findNewHighValueCustomers()

View database designed to

support query

Page 26: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

Events at the core

OrderService

Order created≪aggregate≫

Order

Page 27: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

DDD: Aggregates publish domain events

Order

OrderLine Item

quantity productId productName productPrice

customerId

Address

street city …

Aggregate

Order created

Domain event

Publishes

when created

or state

changes

Page 28: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

Business logic explicitly invoking event publishing API

≪service≫ OrderService

≪aggregate≫ Order

DomainEvent Publisher

placeOrder(…)

new(…)

≪event≫ OrderCreated

publish(…)

new(…)

• Simple • Easy to adapt existing code

But • Events are not automatic • Tricky to publish messages transactionally

publish(…)

Page 29: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

Use event sourcingEvent table

Entity type Event id

Entity id

Event data

Order 902101 …OrderApproved

Order 903101 …OrderShipped

Event type

Order 901101 …OrderCreated

≪aggregate≫ Order

List<Event> process(CreateOrderCommand)void apply (OrderCreatedEvent)

List<Event> process(CancelOrderCommand)void apply (OrderCanceledEvent)

Reliable publishing, aggregate history, auditing, …. YET radically different

Event-based persistence Event-based business logic

+

Page 30: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

Summary

Events play a role at every level of an architecture

Order created

Page 31: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

Summary: aggregates publish events

Order created≪aggregate≫

Order

Page 32: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

Summary: services publish events

Order created≪Aggregate≫ Order

Order Service

Page 33: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

Summary: applications publish events

Order created

≪Aggregate≫ Order

Order Service

E-commerce application

Page 34: OReilly SACON2018 - Events on the outside, on the inside, and at the core

@crichardson

@crichardson [email protected]

http://learn.microservices.io

Questions?ctwsoftarchconf18


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