Introduction

This project aims to demonstrate how Kafka works with Spring Cloud Stream in distributed systems. This project simulates an Order Management system containing contains three services: Checkout Service, Order Service and Fulfillment Service communicating via two Kafka topics: OrderCreated and OrderProcessed. Each service can be scaled up horizontally by adding more instance. The order process is triggered via a REST API sent from the client side to Checkout Service as below.

When a new order is placed, we produce a message to Kafka with the order details and use the customer ID as the message key to ensures that all events related to the same customer (based on customer ID) are processed sequentially by assigning them to the same partition. We will create OrderCreated and OrderProcessed topic with two partitions to demo how this mechanism works.

Tech stack

JDK 11, Gradle, Spring boot, Spring Cloud Stream, Kafka, Docker Compose

How to get started?

We need to build up Kafka with a Zookeeper, a broker and two topics using docker-compose:

docker-compose up

We can start this project via below gradle commands:

gradle build
gradle bootRun

CURL to check out an order

curl --location --request POST 'localhost:8080/app/order/999?customerId=9'

We can also access to kafka ui via http://localhost:8088 which was created by docker-compose to obverse created messages, and the topic partition assigned to them.