Microservices in Java and Scala (sfscala)

@crichardson

Microservices in Java and Scala

Chris Richardson

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

@crichardson [email protected] http://microservices.io http://eventuate.io http://plainoldobjects.com

Copyright © 2015. Chris Richardson Consulting, Inc. All rights reserved

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About Chris

@crichardson

About Chris

Consultant and trainer focusing on

microservices (public class: April 28th, Oakland, CA)

http://www.chrisrichardson.net/

@crichardson

About Chris

Founder of a startup that is creating a platform that makes it easy for

application developers write microservices

(http://eventuate.io)

@crichardson

For more information

http://bit.ly/eventsmarch17

AgendaWhy a pattern language for microservices?

Monolith architecture vs. microservices

Developing microservices with event sourcing and CQRS

Microservices in Java

Microservices in Scala Example: real-time, collaborative Kanban board application

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In 1986…

http://en.wikipedia.org/wiki/Fred_Brooks

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Yet 30 years later….

If you __________________ a puppy will die Therefore you must _______________

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Quiz - fill in the blanks….

mutate state

use monads

use objects

use functions

block a thread

use async.

make a REST call

send a messageuse Spring

use ….

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How we make decisions

Decide using

emotions

Rationalize with our intellect

http://en.wikipedia.org/wiki/Mahout

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The structure of a pattern

=

Great framework for discussing and thinking about technology

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The structure of a pattern

Resulting context

aka the situation

Name

Context

Problem

Related patterns

(conflicting) issues etc to address Forces

Solution

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In theory:

We can build a modular monolith

But in practice:

We build a big ball of mud

Microservices are not a silver bullet but …

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The benefits typically outweigh the drawbacks

for large, complex applications

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Build and deliver better software faster

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Easily try other technologies

... and fail safely






Data management patterns

Database per Service

Event-driven architecture

Shared database

Event sourcing

Transaction log tailing

Database triggers

Application events

CQRS

Database architecture

Database per Service

Orders Service Customer Service

Order Database

Customer Database

Sharded SQL

NoSQL DB

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Customer management

How to maintain invariants?

Order management

Order Service

placeOrder()

Customer Service

updateCreditLimit()

Customer

creditLimit ...

has ordersbelongs toOrder

total

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

?

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Event-driven architecture

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How atomically update database and publish an event

Order Service

Order Database

Message Broker

insert Order

publish OrderCreatedEvent

dual write problem

?

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Reliably generating events

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Use event-sourcingEvent table

Aggregate type

Event id

Aggregate id

Event data

Order 902101 …OrderApproved

Order 903101 …OrderShipped

Event type

Order 901101 …OrderCreated

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Replay events to recreate state

Order

state

OrderCreated(…) OrderAccepted(…) OrderShipped(…)

Events

Periodically snapshot to avoid loading all events

But what about queries?

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Command Query Responsibility Segregation (CQRS)

Command side

Commands

Aggregate

Event Store

Events

Query side

Queries

(Materialized) View

Events

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Query-side design

Event Store

Updater

View Updater Service

Events

Reader

HTTP GET Request

View Query Service

View Store

e.g. MongoDB

Neo4J CloudSearch

update query

Eventuate architecture

Eventuate platform

Multiple flavors of client frameworks

“Traditional Java” mutable object-oriented domain objects

https://github.com/cer/event-sourcing-examples/tree/master/java-spring

Functional Scala with immutable domain objects

https://github.com/cer/event-sourcing-using-scala-typeclasses

Hybrid OO/Functional Scala with immutable domain objects

https://github.com/cer/event-sourcing-examples/tree/master/scala-spring






Customer command side

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The Customer aggregate

creditLimit creditReservations : Map<OrderId, Money>

Customer

List<Event> process(CreateCustomerCommand cmd) { … } List<Event> process(ReserveCreditCommand cmd) { … } … void apply(CustomerCreatedEvent anEvent) { … } void apply(CreditServedEvent anEvent) { … } …

State

Behavior

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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 … new CreditReservedEvent(); }

public void apply( CreditReservedEvent event) { // update state this.xyz = event.xyz }

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Customer command processing

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Customer applying events

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Creating an order

save() concisely specifies: 1.Creates Order aggregate 2.Processes command 3.Applies events 4.Persists events

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Event handling in Customers

1. Load Customer aggregate 2. Processes command 3. Applies events 4. Persists events

Triggers BeanPostProcessor Durable subscription name

Customer - query side

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MongoDB view: customer and their order history

{ "_id" : "0000014f9a45004b 0a00270000000000", "_class" : "net.chrisrichardson…..views.orderhistory.CustomerView", "version" : NumberLong(5), "orders" : { "0000014f9a450063 0a00270000000000" : { "state" : "APPROVED", "orderId" : "0000014f9a450063 0a00270000000000", "orderTotal" : { "amount" : "1234" } }, "0000014f9a450063 0a00270000000001" : { "state" : "REJECTED", "orderId" : "0000014f9a450063 0a00270000000001", "orderTotal" : { "amount" : "3000" } } }, "name" : "Fred", "creditLimit" : { "amount" : "2000" } }

Denormalized = efficient lookup

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Query-side event handler that updates customer view

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Updating and query view using Spring Data for MongoDB...






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Functional Customer aggregate

Customer

creditLimit creditReservations …

CustomerAggregate

processCommand(Account, Command) : Seq[Events]

applyEvent(Account, Event) : Account

Immutable state Behavior

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Aggregate type classesUsed by

Event Store to

reconstitute aggregates

Hardwired

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Customer Aggregate….State

Behavior

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…command processing…

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… applying events






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Kanban board example

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ArchitectureCreate/update boards

and tasks

Change notifications Materialized views

Event Store

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Demo

Summary

Microservices are not a silver bullet but they are the best choice for large/complex applications

Use an event-driven microservices architecture

Build services using event sourcing + CQRS

Using a language/framework specific programming model

@crichardson

@crichardson [email protected]

http://bit.ly/eventsmarch17

Questions?

Microservices in Java and Scala (sfscala)

Software