Book Image

Mastering Akka

By : Christian Baxter
Book Image

Mastering Akka

By: Christian Baxter

Overview of this book

For a programmer, writing multi-threaded applications is critical as it is important to break large tasks into smaller ones and run them simultaneously. Akka is a distributed computing toolkit that uses the abstraction of the Actor model, enabling developers to build correct, concurrent, and distributed applications using Java and Scala with ease. The book begins with a quick introduction that simplifies concurrent programming with actors. We then proceed to master all aspects of domain-driven design. We’ll teach you how to scale out with Akka Remoting/Clustering. Finally, we introduce Conductr as a means to deploy to and manage microservices across a cluster.
Table of Contents (17 chapters)
Mastering Akka
Credits
About the Author
Acknowledgments
About the Reviewer
www.PacktPub.com
Preface

Event sourcing primer


I'll try and keep the theory information a little lighter here, as there is a ton of practical, hands on stuff to go over with Akka Persistence. Still, it's worth going over the high-level concepts in a bit more detail first so that you're mentally prepared to attack the code changes that we'll make.

As I stated in the opener, event sourcing is a technique where, instead of storing the current state of the data explicitly, we store the event stream for a particular entity. Using that event stream, we can arrive at the current state when necessary by replaying the events in memory within our code. We also have the added benefit of having a full audit log for each entity instance that can provide all kinds of benefits, which I'll break out in this section.

At the heart of the event sourcing model, there is the simple concept of Action (command) and Reaction (event), depicted in the following diagram:

As users interact with your system, their actions (represented in the...