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Event-Sourcing+CQRS example application

This example application is the money transfer application described in my talk Building and deploying microservices with event sourcing, CQRS and Docker. This talk describes a way of architecting highly scalable and available applications that is based on microservices, polyglot persistence, event sourcing (ES) and command query responsibility segregation (CQRS). Applications consist of loosely coupled components that communicate using events. These components can be deployed either as separate services or packaged as a monolithic application for simplified development and testing.

Built using the Eventuate platform

<a href="http://eventuate.io"><img src="http://eventuate.io/i/logo.gif"> </a>

Read the <a href="http://eventuate.io">overview</a> or look at the other <a href="http://eventuate.io/exampleapps.html">example applications</a>.

Big ideas

This example illustrates several important concepts:

About the example application

This example application provides a REST API for creating and viewing bank accounts and transferring money between them.

The following diagram shows the architecture:

Money transfer architecture

There are the following services:

There is also an API gateway service that acts as a Facade in front of the services.

About the examples

There are currently the following versions of the example application:

Other examples will be added shortly including a Scala/Play example.

For more information, please see the wiki

About the Eventuate Platform

The application is built using Eventuate, which is an application platform for writing transactional microservices. It provides a simple yet powerful event-driven programming model that is based on event sourcing and Command Query Responsibility Segregation (CQRS). Eventuate solves the distributed data management problems inherent in a microservice architecture. It consists of a scalable, distributed event store and client libraries for various languages and frameworks including Java, Scala, and the Spring framework.

There are two versions of Eventuate:

There is also an embedded test event store, which is great for integration tests.

Building and running the microservices

This is a Gradle project. However, you do not need to install Gradle since it will be downloaded automatically. You just need to have Java 8 installed.

The details of how to build and run the services depend slightly on whether you are using Eventuate SaaS or Eventuate Local.

Building and running using Eventuate SaaS

First, must sign up to get your credentials in order to get free access to the SaaS version.

Next, build the application

cd java-spring
./gradlew assemble

Next, you can launch the services using Docker Compose:

docker-compose up -d

Finally, you can open the home page, which is served up by the API Gateway: http://$DOCKER_HOST_IP:8080

Note: DOCKER_HOST_IP is the IP address of the machine where Docker is running, e.g. the IP address of the VirtualBox VM.

Building and running using Eventuate Local

First, build the application

cd java-spring
./gradlew assemble -P eventuateDriver=local

Next, launch the services using Docker Compose:

export DOCKER_HOST_IP=...
docker-compose -f docker-compose-eventuate-local.yml up -d

Note: You need to set DOCKER_HOST_IP before running Docker Compose. This must be an IP address or resolvable hostname. It cannot be localhost. See this guide to setting DOCKER_HOST_IP for more information.

Finally, you can open the home page, which is served up by the API Gateway: http://$DOCKER_HOST_IP:8080