4. Making History with Event Sourcing | Mastering Akka

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Mastering Akka

By : Christian Baxter

3.7 (6)

Mastering Akka

3.7 (6)

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.

Preface

Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Free Chapter

1. Building a Better Reactive App

1. Building a Better Reactive App

Understanding the initial example app

Working with the example application

So what's wrong with this application?

Summary

2. Simplifying Concurrent Programming with Actors

2. Simplifying Concurrent Programming with Actors

Understanding the actor model's origin

Differentiating concurrency and parallelism

Using Akka actors for safe concurrency

A word on dispatchers in Akka

Mailbox types in Akka

Refactoring a bad actor to FSM

Testing your Akka actors

Summary

3. Curing Anemic Models with Domain-Driven Design

3. Curing Anemic Models with Domain-Driven Design

What is DDD?

Identifying anemic vs rich models

Designing our DDD refactor

Understanding the refactored bookstore code

Fixing the transaction in the order creation process

Improvements needed for the refactor

Refactoring homework

Summary

4. Making History with Event Sourcing

4. Making History with Event Sourcing

Event sourcing primer

Akka Persistence for event sourcing

Using Cassandra for our persistent store

Refactoring the inventory management module

The refactored sales order processing module

Refactoring homework

Summary

5. Separating Concerns with CQRS

5. Separating Concerns with CQRS

A brief history of CQRS

CQRS in the event sourced world

Designing our read model implementation

Implementing the Book read model

Refactoring sales order processing

Playing around with the new application

Refactoring homework

Closing comments

Summary

6. Going with the Flow with Akka Streams

6. Going with the Flow with Akka Streams

Understanding the Reactive Streams API

The Akka Streams API

Refactoring the view building code

Refactoring homework

Summary

7. REST Easy with Akka HTTP

7. REST Easy with Akka HTTP

Creating RESTful HTTP interfaces

Comparing Akka HTTP to Spray

Creating RESTful interfaces with Akka HTTP

Invoking RESTful APIs with Akka HTTP

Refactoring homework

Summary

8. Scaling Out with Akka Remoting/Clustering

8. Scaling Out with Akka Remoting/Clustering

Using Akka Remoting

Using Akka Clustering

Using clustering in the bookstore application

Summary

9. Managing Deployments with ConductR

9. Managing Deployments with ConductR

An overview of ConductR

Installing and setting up ConductR locally

Using the ConductR CLI

Preparing your services for ConductR

Refactoring the bookstore for ConductR

Building and deploying the bookstore bundles

Testing the bookstore modules in ConductR

Summary

10. Troubleshooting and Best Practices

10. Troubleshooting and Best Practices

Refactoring retrospective

Troubleshooting and best practices for actors

Troubleshooting and best practices for Akka HTTP

Troubleshooting and best practices for Akka Clustering/Akka Remoting

Further reading

Summary

Using Cassandra for our persistent store

In Chapter 1, Building a Better Reactive App, in the section titled Cassandra to the rescue, I talked about why Cassandra will be a good fit for our bookstore application. It's distributed and highly available with great performance on the write side. It seems really tailor-made to fit what an event sourced application needs to do. In this section, we will get it installed and then go over the Akka config, which you will need to use it for both the AsyncWriteJournal and the SnapshotStore.

Installing Cassandra

Thanks to our decision to use Docker, there is no real install that we need to do to get Cassandra set up on our local systems. In this chapter, in the Docker Compose configuration (contained in the docker-compose.yml file found at the root of the bookstore app directory structure) we have replaced Postgres with Cassandra. All we need to do is launch the bookstore app as we have done previously (via docket-build.sh and then launch.sh) and we will...

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