Book Image

Event-Driven Architecture in Golang

By : Michael Stack
5 (1)
Book Image

Event-Driven Architecture in Golang

5 (1)
By: Michael Stack

Overview of this book

Event-driven architecture in Golang is an approach used to develop applications that shares state changes asynchronously, internally, and externally using messages. EDA applications are better suited at handling situations that need to scale up quickly and the chances of individual component failures are less likely to bring your system crashing down. This is why EDA is a great thing to learn and this book is designed to get you started with the help of step-by-step explanations of essential concepts, practical examples, and more. You’ll begin building event-driven microservices, including patterns to handle data consistency and resiliency. Not only will you learn the patterns behind event-driven microservices but also how to communicate using asynchronous messaging with event streams. You’ll then build an application made of several microservices that communicates using both choreographed and orchestrated messaging. By the end of this book, you’ll be able to build and deploy your own event-driven microservices using asynchronous communication.
Table of Contents (18 chapters)
1
Part 1: Event-Driven Fundamentals
5
Part 2: Components of Event-Driven Architecture
12
Part 3: Production Ready

Command and Query Responsibility Segregation

Command and Query Responsibility Segregation (CQRS) is a simple pattern to define. Objects are split into two new objects, with one being responsible for commands and the other responsible for queries.

Figure 2.9 – Applying CQRS to an object

Figure 2.9 demonstrates just how simple the concept might be, but the devil is in the implementation details as they say. The definitions for Command and Query are the same as they are for Command-Query Separation (CQS):

  • Command: Performs a mutation of the application state
  • Query: Returns application state to the caller

Note

In CQRS, just as it is in CQS, an action can either be a command or a query but not both.

The problem being solved

The domain models we’ve developed with the help of domain experts may be very complex and large. These complex models may not be useful or too much for our queries. Conversely, we may have complex queries...