Akka in Action workshop #ScalaMatsuri 2018

Copyright © 2018 TIS Inc. All rights reserved.
Akka in Action workshop
Scala Matsuri 2018
Yugo Maede
@yugolf
The preparation for this workshop.
https://github.com/akka-ja/akka-in-action/tree/matsuri/chapter-up-and-running#the-preparation

Copyright © 2018 TIS Inc. All rights reserved. 2
Who am I?
Yugo Maede @yugolf
TIS Inc.
research and development using Akka, Scala and others
Translated
Akkaを使ったシステム開発や研究活動をやっています。
仲間募集開始！！
We are recruiting colleagues to
work together with us.

TISカジュアルはじめました
2018.3.1
TIS casual has started!
We are hiring!

Todayʼs Topics
Building a minimal Akka app
The first step for Akka
• How to implement Apps by using Akka
• How to study Akka for the future
Akkaで最⼩のアプリケーションを構築する
Akkaを使った実装の取っ掛かりに

Material
教材は『Akka実践バイブル』
✦here

Akka in Action
『Akka実践バイブル』の内容
Appendix. Using Akka from Java
https://www.manning.com/books/akka-in-action

Agenda
• Introduction
• Chapter1. Introducing Akka
• Chapter2. Up and running
• Fetching a project template
• Building a minimal Akka app for the cloud
4 exercises
• Deploying to Heroku
• Conclusion
アジェンダ

Chapter 1. Introducing Akka
8
第1章 Akkaの紹介

Chapter 1. Introducing Akka
Akkaとは／概要／従来型との違い／アクターのプログ
ラミングモデル／Akkaのアクター
1.1. What is Akka?
1.2. Actors: a quick overview
1.3. Two approaches to scaling: setting up our example
1.4. Traditional scaling
1.5. Scaling with Akka
1.6. Actors: one programming model to rule up and out
1.7. Akka actors

What is Akka?
Akkaは並⾏・分散アプリケーションのためのツール
キット
•The toolkit for concurrent and distributed
applications
•scale applications both up
and out on the JVM
•keep the complexity
relatively low while an
application scales

Actors: a quick overview
アクターからアクターへメッセージを送信、受信した
メッセージを到着順に処理
User
Actor processes messages
in order of arrival
TicketSeller
Buy
Buy
Buy
mailbox
ticketSeller ! Buy(tickets)

Traditional scaling and Akka scaling
アクターと伝統的なアプローチの⽐較
• Traditional • Akka

Traditional scaling and Akka scaling
ゴール：データは永続性あるものに、機能はインタラク
ティブに、サービスは疎結合に、そして障害に強く
Goal Traditional approach Akka approach
Make data durable,
even if the
application restarts
or crashes.
Use the database as
one big shared
mutable state.
Continue to use in-memory
state. Changes to the state
are sent as messages to a
log.
Provide interactive
features
Poll the database,
even if there’s no
change in the data.
Push events to interested
parties, only when there’s
a significant event.
Decoupling of services Add a message queue
for asynchronous
processing.
No need to add a message
queue; actors are
asynchronous by definition.
Prevent failure of the
total system when
critical services fail
predicting all
failure scenarios and
catching exceptions.
no impact on the stability
of the other components.

Actors: one programming model to rule up and out
単⼀のプログラミングモデルでスケールアップとスケー
ルアウトを実現
The actor model decouples from the number of threads or the
number of servers.

Akka actors: Actor System
Akkaのアクターはアクターシステムを作成することか
ら
https://doc.akka.io/docs/akka/2.5/general/supervision.html
val system = ActorSystem("TeamChat")

Akka actors: ActorRef and Mailbox and Actor
ActorRefに到着したメッセージは⼀時的にメールボッ
クスに保存し到着順に処理する

Chapter 2. Up and running
17
第2章最⼩のAkkaアプリケーション

18
•Fetching a project template
•Building a minimal Akka app for the cloud
•Deploying to Heroku
• プロジェクトテンプレートの取得

Fetching a project template
Gitからプロジェクトを取得してアプリケーションを実⾏
• Clone the example project from github.com
$git clone https://github.com/akka-ja/akka-in-action.git
$cd akka-in-action/chapter-up-and-running/
$sbt run
https://github.com/akka-ja/akka-in-action/tree/matsuri/chapter-up-and-running#the-commands-using-this-workshop
• Start the app
[info] Running com.goticks.Main
INFO [Slf4jLogger]: Slf4jLogger started
INFO [go-ticks]: RestApi bound to /0:0:0:0:0:0:0:0:5000
INFO [go-ticks]: Success to bind to 0.0.0.0:5000

The structure of the project
プロジェクトの構造
configuration files and other resources
source codes
test codes
built files
for building by sbt
for executing on Heroku
https://www.jetbrains.com/idea/download/

Ticket-selling service
チケット販売サービス
イベント作成／キャンセル／⼀覧取得／チケット購⼊
• Get all events
• Buy tickets
• Create an event
• Cancel an event
Ticket-selling
service

Letʼs run the app
まずは、動かしてみましょう！
HTTPリクエストのツールをインストールしてアプリを起動
• Prepare for executing http requests
• install HTTPie or Advanced REST client
- CLI: HTTPie (https://httpie.org/)
- GUI: Advanced REST client(Chrome Extensions)
https://chrome.google.com/webstore/detail/advanced-rest-
client/hgmloofddffdnphfgcellkdfbfbjeloo
$brew install httpie

How to use HTTPie
HTTPieを使ったHTTPリクエストの送信⽅法
• CLI: HTTPie
$http POST localhost:5000/events/RHCP tickets:=10
HTTP/1.1 201 Created
Content-Length: 28
Content-Type: application/json
Date: Sat, 10 Mar 2018 09:27:25 GMT
Server: GoTicks.com REST API
{
"name": "RHCP",
"tickets": 10
}

How to use REST client
Advanced REST clientを使ったリクエストの送信⽅法
• GUI: Advanced REST client(Chrome Extensions)
(1) (2)
(3)
(4)
(8)
http://localhost:5000/events/RHCP
(5)
(6)
(7)
{"tickets":10}

How to send 4 types of HTTP requests
４つのHTTPリクエストの送信⽅法
• Create an event
• Get all events
• Buy tickets
• Cancel an event
$http GET localhost:5000/events
$http POST localhost:5000/events/RHCP/tickets tickets:=2
$http DELETE localhost:5000/events/RHCP/

イベントの作成、参照、購⼊、、、キャンセル、、、
>get all events
>buy 2 “RHCP” tickets
>get all events
> create “RHCP” event with 10 tickets
> create “ScalaMatsuri” event with 20 tickets
> cancel “ScalaMatsuri”
> get all events
Letʼs run the app

27
• 最⼩のAkkaアプリケーションをクラウドに構築

Fetching a project template for workshop
ワークショップ⽤ブランチの取得
$ git checkout matsuri

ActorSystem
“go-ticks”
29
The structure of the application
アプリケーションの構造
Main
HTTP Server
HTTP Route
RestApi
Actor
BoxOffice
Actor
TicketSeller
run
new
create
create
create

The structure of the Actors
アクターの構造
チケット売り場とチケット販売員
RHCP
Scala
Matsuri
boxOffice
create
Add/Buy/Cancel/…
Actor
BoxOffice
Actor
TicketSeller

Exercise 0. Create ActorSystem
31
演習0．アクターシステムの⽣成

ActorSystem
“go-ticks”
32
Create ActorSystem
アクターシステムの⽣成
Main
HTTP Server
HTTP Route
RestApi
Actor
BoxOffice
Actor
TicketSeller
run
new
create
create
create

Create “go-ticks” ActorSystem
ActorSystem「go-ticks」の⽣成
0.0.[Main] create ActorSystem
Run the App
implicit val system = ActorSystem(“go-ticks”)
$ sbt run
...
[info] Running com.goticks.Main

Exercise 1. Create an event
34
演習１．イベントの作成

HTTP Route
RestApi
Actor
BoxOffice
Actor
TicketSeller
CreateEvent
create
EventCreated
EventExists
POST
/events/RHCP
Created 201
BadRequest 400
Add
イベントを作成するフロー
The flow of creating an event

The flow of creating an event: implement points
実装するところ
Actorの⽣成とメッセージ送信(Add/ EventCreated)
HTTP Route
RestApi
Actor
BoxOffice
Actor
TicketSeller
CreateEvent
create
AddEventCreated
EventExists
POST
/events/RHCP
Created 201
BadRequest 400

Exercise 1: Define and create Actors and send messages
演習１：TicketSellerアクターの⽣成、Addメッセージ
の送信、EventCreatedメッセージの返信
• Create TicketSeller actor
1.1.[TicketSeller] define actor factory method
1.2.[BoxOffice ] create TicketSeller actor
• Send Add message from BoxOffice to TicketSeller
1.3.[TicketSeller] define message protocol
1.4.[TicketSeller] behavior when receive messages
1.5.[BoxOffice ] send Add message
• Return EventCreated message from BoxOffice to RestApi
1.6.[BoxOffice ] return EventCreated message

Exercise 1: Run the app
イベント作成の動作確認
Run the app
$cd akka-in-action/chapter-up-and-running/
$sbt run
...
Send a HTTP request
...
{
"name": "RHCP",
"tickets": 10
}

Create TicketSeller actor
TicketSellerアクターの⽣成
1.1.[TicketSeller] define actor factory method
1.2.[BoxOffice ] create TicketSeller actor
object TicketSeller {
def props(event: String) = Props(new TicketSeller(event))
}
class BoxOffice(implicit timeout: Timeout) extends Actor {
...
def createTicketSeller(name: String) =
context.actorOf(TicketSeller.props(name), name)
def receive = {
case CreateEvent(name, tickets) =>
def create() = {
val eventTickets = createTicketSeller(name)
...
}
context.child(name).fold(create())(_ => sender() ! EventExists)
}
BoxOffice TicketSeller
create

Send Add message from BoxOffice to TicketSeller
Addメッセージの送信（BoxOffice->TicketSeller）
1.5.[BoxOffice ] send Add message
case class Add(tickets: Vector[Ticket])
}
...
def receive = {
def create() = {
...
eventTickets ! TicketSeller.Add(newTickets)
}
class TicketSeller(event: String) extends Actor {
import TicketSeller._
var tickets = Vector.empty[Ticket]
def receive = {
case Add(newTickets) => tickets = tickets ++ newTickets
}
Add

Return EventCreated message from BoxOffice to RestApi
EventCreatedメッセージの返信(RestApi<-BoxOffice)
1.6.[BoxOffice ] return EventCreated message
...
def receive = {
def create() = {
...
sender() ! EventCreated(Event(name, tickets))
}
}
RestApi BoxOffice
EventCreated

Exercise 1: learned
アクターの⽣成、メッセージ送信、メッセージプロトコ
ルの定義、メッセージを受信したときのふるまい
• create Actor
• send messages
• behavior when receive messages
• define message protocol
context.actorOf(TicketSeller.props(name), name)
case class Add(tickets: Vector[Ticket])
}
def receive = {
case Add(newTickets) => ...
def props(event: String) = Props(new TicketSeller(event))
}

Exercise 2. Buy tickets
演習２．チケットの購⼊

The flow of buying tickets
チケットを購⼊するフロー
GetTicketsPOST
/events/RHCP/tickets
Created 201
NotFound 404
HTTP Route
RestApi
Actor
BoxOffice
Actor
TicketSeller
Buy
Tickets

GetTickets
Buy
Tickets
POST
/events/RHCP/tickets
Created 201
NotFound 404
HTTP Route
RestApi
Actor
BoxOffice
Actor
TicketSeller
メッセージ送信(Buy/ Tickets)
The flow of buying tickets: implement points

Exercise 2: Send Buy message and return Tickets message
演習２：Buyメッセージを送信して、Ticketsメッセー
ジを返信する
• Send Buy message from BoxOffice to TicketSeller
- return Tickets message
2.3.[BoxOffice ] forward Buy message

チケット購⼊の動作確認
$sbt run
...
...
{
"entries": [
{
"id": 1
},
{
"id": 2
}
],
"event": "RHCP"
}
Run the app
Send a HTTP request

Send Buy message from BoxOffice to TicketSeller
送信元アクターに直接返信させるためforwardする
- return Tickets message
2.3.[BoxOffice ] forward Buy message
case class Buy(tickets: Int)
case class Tickets(event: String, entries: Vector[Ticket] = Vector.empty[Ticket])
def receive = {
case Buy(nrOfTickets) =>
val entries = tickets.take(nrOfTickets)
if(entries.size >= nrOfTickets) {
sender() ! Tickets(event, entries)
tickets = tickets.drop(nrOfTickets)
} else sender() ! Tickets(event)
def receive = {
case GetTickets(event, tickets) =>
...
def buy(child: ActorRef) = child.forward(TicketSeller.Buy(tickets))
Buy
BoxOffice
Tickets

Exercise 2: learned
メッセージの転送
• forward message
child.forward(TicketSeller.Buy(tickets))

Exercise 3. Get all events
50
演習３．イベント⼀覧の取得

The flow of getting all events
イベント⼀覧を取得するフロー
GetEventsGET
/events/
OK 200 Events
HTTP Route
RestApi
Actor
BoxOffice
Actor
TicketSeller
GetEvent
None
GetEvent
Event
Events

GetEvents
GetEvent
Event
GET
/events/
OK 200 Events
GetEvent
None
Events
HTTP Route
RestApi
Actor
BoxOffice
Actor
TicketSeller
The flow of getting all events: implement points
メッセージ送信(GetEvent/ None/ Event/ Events)

Exercise 3: Send GetEvent message and return Event message
• Return Event
3.1.[TicketSeller] defines message protocol
- return Event message
• Send GetEvent message from BoxOffice to self
3.3.[BoxOffice ] sends GetEvent message to self
• Define behavior when receive GetEvent message
3.4.[BoxOffice ] doesn’t find a child actor:
- return None message
3.5.[BoxOffice ] finds a child actor:
- forward GetEvent message
• Return Events message
3.6.[BoxOffice ] returns Events message to sender
演習３：GetEventメッセージを送信して、Eventメッ
セージを返信する

チケット⼀覧取得の動作確認
$sbt run
...
...
$http GET localhost:5000/events/
HTTP/1.1 200 OK
...
{
"events": [
{
"name": "RHCP",
"tickets": 8
}
]
}
Run the app
Send a HTTP request

Return Event
3.1.[TicketSeller] defines message protocol
def receive = {
...
case GetEvent => sender() ! Some(BoxOffice.Event(event, tickets.size))
case object GetEvent
}
GetEventメッセージを受信したら、Eventメッセージ
を返す
Event

Send GetEvent message from BoxOffice to self
GetEventメッセージを⾃⾝（self）に送信する
3.3.[BoxOffice ] sends GetEvent message to self
...
def receive = {
...
case GetEvents =>
import akka.pattern.ask
def getEvents = context.children.map { child =>
self.ask(GetEvent(child.path.name)).mapTo[Option[Event]]
}
BoxOffice
GetEvent

Define behavior when receive GetEvent message
GetEventメッセージを受信したときのふるまい
3.4.[BoxOffice ] doesn’t find a child actor:
- return None message
3.5.[BoxOffice ] finds a child actor:
- forward GetEvent message
...
def receive = {
...
case GetEvent(event) =>
def notFound() = sender() ! None
def getEvent(child: ActorRef) = child forward TicketSeller.GetEvent
context.child(event).fold(notFound())(getEvent)
...
GetEvent
None

Return Events message
pipeを使って、処理完了時にFuture内の値（Events）
を送信元に返信する
3.6.[BoxOffice ] returns Events message to sender
...
def receive = {
...
case GetEvents =>
import akka.pattern.ask
import akka.pattern.pipe
def getEvents = context.children.map { child =>
}
def convertToEvents(f: Future[Iterable[Option[Event]]]) =
f.map(_.flatten).map(l=> Events(l.toVector))
pipe(convertToEvents(Future.sequence(getEvents))) to sender()
...
RestApi BoxOffice
Events

Exercise 3: learned
応答が必要なメッセージ、⾃⾝へのメッセージ送信
send message which needs a response
send message to myself
pipe(convertToEvents(Future.sequence(getEvents))) to sender()

Exercise 4. Cancel an event
60
演習４．イベントのキャンセル

The flow of Canceling an event
イベントをキャンセルするフロー
CancelEvent
Cancel
Event
DELETE
/events/RHCP
OK 200 None
PoisonPill
HTTP Route
RestApi
Actor
BoxOffice
Actor
TicketSeller

CancelEvent
Cancel
Event
DELETE
/events/RHCP
OK 200 None
PoisonPill
HTTP Route
RestApi
Actor
BoxOffice
Actor
TicketSeller
The flow of Canceling an event: implement points
メッセージ送信(Cancel/ Event)、アクターの停⽌

Exercise 4: Send Cancel message and stop TicketSeller actor
演習４：Cancelメッセージの送信とTicketSellerアク
ターの停⽌
Send Cancel message from BoxOffice to TicketSeller
return Event message
send PoisonPill to self
4.3.[BoxOffice ] forward Cancel message

$sbt run
...
...
$http GET localhost:5000/events/
...
$http DELETE localhost:5000/events/RHCP
HTTP/1.1 200 OK
...
{
"name": "RHCP",
"tickets": 8
}
Run the app
Send a HTTP request
イベントキャンセルの動作確認

Send Cancel message from BoxOffice to TicketSeller
PoisonPillメッセージを送信してアクターを停⽌する
- send PoisonPill to self
4.3.[BoxOffice ] forward Cancel message
case object Cancel
}
def receive = LoggingReceive {
case Cancel =>
sender() ! Some(BoxOffice.Event(event, tickets.size))
self ! PoisonPill
class BoxOffice(implicit timeout: Timeout) extends Actor with ActorLogging {
case CancelEvent(event) =>
def notFound() = sender() ! None
def cancelEvent(child: ActorRef) = child forward TicketSeller.Cancel
context.child(event).fold(notFound())(cancelEvent)

RestApi
RestRoutes trait
trait RestRoutes extends BoxOfficeApi with EventMarshalling {
import StatusCodes._
def routes: Route = eventsRoute ~ eventRoute ~ ticketsRoute
def eventsRoute = ...
def eventRoute =
pathPrefix("events" / Segment) { event =>
pathEndOrSingleSlash {
post {
...
} ~
get {
...
} ~
delete {
// DELETE /events/:event
onSuccess(cancelEvent(event)) {
_.fold(complete(NotFound))(e => complete(OK, e))
}
}
}
}
RestRoutesトレイト

RestApi
BoxOfficeApi trait
trait BoxOfficeApi {
import BoxOffice._
def createBoxOffice(): ActorRef
implicit def executionContext: ExecutionContext
implicit def requestTimeout: Timeout
lazy val boxOffice = createBoxOffice()
...
def cancelEvent(event: String) =
boxOffice.ask(CancelEvent(event))
.mapTo[Option[Event]]
...
}
BoxOfficeApiトレイト

Exercise 4: learned
アクターの停⽌、RestAPI
stop Actor
Rest API
case Cancel =>
sender() ! Some(BoxOffice.Event(event, tickets.size))
self ! PoisonPill
def routes: Route = eventsRoute ~ eventRoute ~ ticketsRoute
def eventRoute =
pathPrefix("events" / Segment) { event =>
pathEndOrSingleSlash {
delete {
// DELETE /events/:event
}

69
• Herokuへのデプロイ

Into the cloud
Create the app on Heroku
$cd ..
$heroku login
$heroku create
Creating app... done, ⬢ vast-harbor-91925
https://vast-harbor-91925.herokuapp.com/ | https://git.heroku.com/vast-harbor-91925.git
Heroku上にアプリケーションを作成する
install heroku CLI
$brew install heroku

Into the cloud
Push the code to Heroku
$git subtree push --preﬁx chapter-up-and-running heroku master
----> Scala app detected
-----> Installing OpenJDK 1.8... done
.... // 依存するライブラリが解決され、ダウンロードされる
....
-----> Compressing...
Done: 68.8M
-----> Launching...
Released v1
https://damp-bayou-9575.herokuapp.com/ deployed to Heroku
To git@heroku.com:damp-bayou-9575.git
* [new branch] master -> master
$ http POST damp-bayou-9575.herokuapp.com/events/RHCP tickets:=250
$ http POST damp-bayou-9575.herokuapp.com/events/RHCP/tickets tickets:=4
Test Heroku instance with HTTPie
ソースコードをHerokuにプッシュして、動作確認

Conclusion
72
まとめ

Conclusion
Done
• built a minimal set of REST services using Akka
Next Exercises
• lost data if the application restarts
• neither scale up nor out
• doesn’t know how to test
• the whole system is down when a server fails
Akkaを使って⼩さなRESTサービスを作りました。
しかし、再起動すると？スケールアウトは？テストは？障害起きると...

Reference materials
74
Amazonとかにレビューを書いてくださる⽅に『Akka実
践バイブル』をプレゼント！！
• メニーコア時代のパラダイムリアクティブシステムを知ろう(ThinkIT)

Akka in Action workshop #ScalaMatsuri 2018

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