Event sourcing and CQRS example

What is this?

This repository contains an example application that uses event sourcing and CQRS to handle credit, debit and balance requests for a bank account.

The application is based on Kotlin, Spring Boot and Spring Cloud Stream. Apache Kafka is used as an event store and an H2 database is used to keep track of the current application state for queries.

How to start it?

Precondition

You need a running zookeeper/kafka instance to be able to start the application.

Docker compose

Start up a kafka instance and the application using the command docker-compose up.

If the application creates an error on startup and cannot contact kafka, probably a timeout might has occured while the application was waiting for kafka to start (this can take a momment depending on your hardware). If this happens, then first start kafka using docker-compose up -d kafka, then wait a minute and start the application using docker-compose up application.

The application is exposed locally on port 8080.

Application start via gradle

The application can be started via Gradle with the command ./gradlew bootRun. Make sure you have a kafka instance available first.

How do i use it?

After starting the application, you can send credit requests as HTTP POST to http://localhost:8080/balance/ACCOUNT-NUMBER-HERE/credit and debit requests to http://localhost:8080/balance/ACCOUNT-NUMBER-HERE/debit. The body payload of those requests must look like { "amount": 200.0 }. To retrieve the balance, send a GET request to http://localhost:8080/balance/ACCOUNT-NUMBER-HERE To retrieve a statement containing the 10 last transations, send a GET request to http://localhost:8080/statement/ACCOUNT-NUMBER-HERE

Examples requests can be imported into Postman using the provided collection bankaccount.postman_collection.json.