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
chris@chrisrichardson.net
http://microservices.io
http://eventuate.io
http://plainoldobjects.com
Copyright © 2015. Chris Richardson Consulting, Inc. All rights reserved

@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

Agenda
Why 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

@crichardson
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

@crichardson
The structure of a pattern
Resulting context
aka the situation
Name
Context
Problem
Related patterns
(conﬂicting) issues
etc to address
Forces
Solution

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 …

@crichardson
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
?

@crichardson
Event-driven architecture

@crichardson
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-sourcing
Event table
Aggregate
type
Event
id
Aggregate
id
Event
data
Order 902101 …OrderApproved
Order 903101 …OrderShipped
Event
type
Order 901101 …OrderCreated

@crichardson
Replay events to recreate
state
Order
state
OrderCreated(…)
OrderAccepted(…)
OrderShipped(…)
Events
Periodically snapshot to avoid loading all events

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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

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

@crichardson
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

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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 classes
Used 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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Architecture
Create/update boards
and tasks
Change notiﬁcations
Materialized
views
Event Store

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 chris@chrisrichardson.net
http://bit.ly/eventsmarch17
Questions?

Microservices in Java and Scala (sfscala)

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