4. Event Driven Architecture

Introduction

In the previous lab we have split up the monolithic application into a microservice architecture powered by RESTful APIs. The communication via REST gives us a higher coupling due to the fact the microservices won’t work when the counterpart is not available. To reduce the coupling even more we are going to use an event driven approach.

In a first step we are going to set up our Apache Kafka cluster which will be our message oriented middleware. We will then reimplement our communication in a reactive messaging approach, to get our system up and running again!

Microservices

To ensure consistency we are going to implement a simple SAGA pattern with choreography. Each order will trigger an event to a shop-order-request topic. The stock microservice will subscribe to this topic and will try to handle the order. If the order was handled successfully by the stock microservice the confirmation will be published or compensated in the case of an error.

Instead of an choreography approach, which other method could be used to ensure the SAGA pattern?

Hint

We could have used an orchestrated approach. To ensure orchestration we would have implemented an orchestrator-microservice, which handles the coordination between the two microservices.

Lab Overview

Environment


4.1 Getting Started

Getting started with the lab environment.

4.2 Docker Environment

Setting up your local docker environment for this lab.

4.3 Reactive Messaging

Reactive Messaging.

4.4 Event Driven with Kafka

Transition from RESTful to event driven messaging.

4.5 Running the Lab

Building the docker image for the order microservice and start the environment.

4.6 Using the Lab

Making requests against the Lab environment.