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Akka Cookbook
Akka Cookbook

Akka Cookbook: Recipes for concurrent, fast, and reactive applications

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Profile Icon Mishra Profile Icon Héctor Veiga Ortiz
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€41.99
Full star icon Full star icon Full star icon Full star icon Half star icon 4.2 (10 Ratings)
Paperback May 2017 414 pages 1st Edition
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Arrow left icon
Profile Icon Mishra Profile Icon Héctor Veiga Ortiz
Arrow right icon
€41.99
Full star icon Full star icon Full star icon Full star icon Half star icon 4.2 (10 Ratings)
Paperback May 2017 414 pages 1st Edition
eBook
€8.99 €32.99
Paperback
€41.99
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Free Trial
Renews at €18.99p/m
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€8.99 €32.99
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Akka Cookbook

Supervision and Monitoring

In this chapter, we will cover the following recipes:

  • Creating child actors of a parent actor
  • Overriding the life cycle hooks of an actor
  • Sending messages to actors and collecting responses
  • Understanding OneForOneStrategy for actors
  • Understanding AllForOneStrategy for actors
  • Monitoring an actor life cycle using DeathWatch

Introduction

In the previous chapter, you learned about some basic and advanced things about Akka actors. In this chapter, you will learn about supervision and monitoring of Akka actors.

Using supervision and monitoring, we can write fault-tolerant systems, which can run continuously for days, months, and years without stopping. Let's see what is meant by fault tolerance.

What is fault tolerance?

Fault tolerance is a property of systems that are intended to be always responsive rather than failing completely in case of a failure. Such systems are known as fault tolerance systems or resilient systems.

In simple words, a fault-tolerant system is one which is destined to continue as more or less fully operational, with perhaps a reduction in throughput or an increase...

Creating child actors of a parent actor

In this recipe, we will learn how to create child actors of an actor. Akka follows a tree-like hierarchy to create actors and it is also the recommended practice.

By following such practices, we can handle failures in actors as the parent can take care of it. Lets see how to do it.

Getting ready

We need to import the Hello-Akka project in the IDE of our choice. The Akka actor dependency that we added in build.sbt is sufficient for most of the recipes in this chapter, so we will skip the Getting ready section in our further recipes.

How to do it...

  1. Create a file named ParentChild...

Overriding the life cycle hooks of an actor

Since we are talking about supervision and monitoring of actors, you should understand the life cycle hooks of an actor. In this recipe, you will learn how to override the life cycle hooks of an actor when it starts, stops, prestarts, and postrestarts.

How to do it...

  1. Create a file called ActorLifeCycle.scala in package com.packt.chapter2.
  2. Add the following imports to the top of the file:
        import akka.actor._ 
import akka.actor.SupervisorStrategy._
import akka.util.Timeout
import scala.concurrent.Await
import scala.concurrent.duration._
import akka.pattern.ask
  1. Create the following messages to be sent to the actors:
        case object Error  
case class StopActor...

Sending messages to actors and collecting responses

In this recipe, you will learn how a parent sends messages to its child, and collects responses from them.

To step through this recipe, we need to import the Hello-Akka project in the IDE.

How to do it...

  1. Create a file, SendMesagesToChilds.scala, in package com.packt.chapter2.
  2. Add the following imports to the top of the file:
        import akka.actor.{ Props, ActorSystem, Actor, ActorRef } 
  1. Create messages to be sent to the actors as follows:
        case class DoubleValue(x: Int) 
case object CreateChild
case object Send
case class Response(x: Int)
  1. Define a child actor. It doubles the value sent to it.
        class DoubleActor extends Actor { 
def receive = {
...

Understanding OneForOneStrategy for actors

In this recipe, you will learn about OneForOneStrategy to implement the let it crash model.

The OneForOneStrategy class is applied when we want to supervise the child actors in such a way that only the failed child would be restarted, resumed, or escalated, not it's siblings. If we don't specify any supervisor strategy, then the default would be OneForOneStrategy. Let's understand it.

The OneForOneStrategy class is useful when actors are not dependent on each other, they are each responsible for a single task, and failure of one actor does not affect another.

To step through this recipe, we need to import the Hello-Akka project in IDE.

How to do it...

  1. Create a file, SupervisorStrategy.scala, in...

Introduction


In the previous chapter, you learned about some basic and advanced things about Akka actors. In this chapter, you will learn about supervision and monitoring of Akka actors.

Using supervision and monitoring, we can write fault-tolerant systems, which can run continuously for days, months, and years without stopping. Let's see what is meant by fault tolerance.

What is fault tolerance?

Fault tolerance is a property of systems that are intended to be always responsive rather than failing completely in case of a failure. Such systems are known as fault tolerance systems or resilient systems.

In simple words, a fault-tolerant system is one which is destined to continue as more or less fully operational, with perhaps a reduction in throughput or an increase in response time because of partial failure of its components.

Even if a components fails, the whole system never gets shut down; instead, it remains operational and responsive with just a decreased throughput.

Similarly, while designing...

Creating child actors of a parent actor


In this recipe, we will learn how to create child actors of an actor. Akka follows a tree-like hierarchy to create actors and it is also the recommended practice.

By following such practices, we can handle failures in actors as the parent can take care of it. Lets see how to do it.

Getting ready

We need to import the Hello-Akka project in the IDE of our choice. The Akka actor dependency that we added in build.sbt is sufficient for most of the recipes in this chapter, so we will skip the Getting ready section in our further recipes.

How to do it...

  1. Create a file named ParentChild.scala in package com.packt.chapter2.
  2. Add the following imports to the top of the file:
        import akka.actor.{ActorSystem, Props, Actor} 
  1. Create messages for sending to actors.
        case object CreateChild 
        case class Greet(msg: String) 
  1. Define a child actor as follows:
        class ChildActor extends Actor { 
          def receive = { 
            case Greet(msg) =&gt...
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Key benefits

  • Covers a discussion on Lagom—the newest launched Akka framework that is built to create complex microservices easily
  • The recipe approach of the book allows the reader to know important and independent concepts of Scala and Akka in a seamless manner
  • Provides a comprehensive understanding of the Akka actor model and implementing it to create reactive web applications

Description

Akka is an open source toolkit that simplifies the construction of distributed and concurrent applications on the JVM. This book will teach you how to develop reactive applications in Scala using the Akka framework. This book will show you how to build concurrent, scalable, and reactive applications in Akka. You will see how to create high performance applications, extend applications, build microservices with Lagom, and more. We will explore Akka's actor model and show you how to incorporate concurrency into your applications. The book puts a special emphasis on performance improvement and how to make an application available for users. We also make a special mention of message routing and construction. By the end of this book, you will be able to create a high-performing Scala application using the Akka framework.

Who is this book for?

If you are a Scala developer who wants to build scalable and concurrent applications, then this book is for you. Basic knowledge of Akka will help you take advantage of this book.

What you will learn

  • Control an actor using the ContolAware mailbox
  • Test a fault-tolerant application using the Akka test kit
  • Create a parallel application using futures and agents
  • Package and deploy Akka application inside Docker
  • Deploy remote actors programmatically on different nodes
  • Integrate Streams with Akka actors
  • Install Lagom and create a Lagom project
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Length: 414 pages
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Table of Contents

11 Chapters
Diving into Akka Chevron down icon Chevron up icon
Supervision and Monitoring Chevron down icon Chevron up icon
Routing Messages Chevron down icon Chevron up icon
Using Futures and Agents Chevron down icon Chevron up icon
Scheduling Actors and Other Utilities Chevron down icon Chevron up icon
Akka Persistence Chevron down icon Chevron up icon
Remoting and Akka Clustering Chevron down icon Chevron up icon
Akka Streams Chevron down icon Chevron up icon
Akka HTTP Chevron down icon Chevron up icon
Understanding Various Akka patterns Chevron down icon Chevron up icon
Microservices with Lagom Chevron down icon Chevron up icon

Customer reviews

Top Reviews
Rating distribution
Full star icon Full star icon Full star icon Full star icon Half star icon 4.2
(10 Ratings)
5 star 70%
4 star 0%
3 star 10%
2 star 20%
1 star 0%
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Amazon Customer Aug 08, 2017
Full star icon Full star icon Full star icon Full star icon Full star icon 5
I have been using Akka for a while now. I've found this book to cover most of my use cases, plus some that I've not encountered yet. The example code is quite clear. I really like the "cookbook" format and would like to see it continue into advance scenarios.
Amazon Verified review Amazon
Amazon Customer Aug 10, 2017
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Great book! I was starting from zero with Akka and in no time I was able to implement the use case I wanted following several recipes. Totally recommended!
Amazon Verified review Amazon
Amazon Customer Jun 11, 2017
Full star icon Full star icon Full star icon Full star icon Full star icon 5
I learnt a lot with this book. Useful and great attention to details. Code examples are helpful.
Amazon Verified review Amazon
kokalos Nov 05, 2020
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Il panorama della programmazione ad attori è abbastanza vasto. Questo libro ha il pregio di trattare in modo incrementale tutti gli aspetti del framework dalla applicazione semplice fino ai micro servizi
Amazon Verified review Amazon
Seth Kong Sep 24, 2017
Full star icon Full star icon Full star icon Full star icon Full star icon 5
I find this book very helpful in applying Akka in my projects. I was reading many books on Akka before but this book is taking me to the next level. If you are looking to build the strong foundation with Akka using Scala this book is for you.
Amazon Verified review Amazon
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