Evolving a service from monolith to microservices with Axon Framework and Axon Server

The goal of this repo is to show how one can develop a well structured monolithic application that can evolve to become a set of microservices using Axon Framework and Axon Server.

This starts as two services, Rental (Monolith) and Payment which work together to run the Axoniq World Wide Bike Rental Service. The Rental service manages the inventory and rental status of bikes. While the Payment service manages payment processing related to a bike rental.

Pre-requisites

The following software must be installed in your local environment:

• JDK version 21.

• Docker-Compose

Quick Start

• An IDE such as Jetbrains IDEA is recommended.

Start Services

Begin by running the PaymentApplication and RentalApplication Services in this order.
This will start a docker image of Axon-Server using run the docker-compose.yaml file found in the root of the project. Once you have both services started you can see them connected to Axon-Server at http://localhost:8024/#overview

From this page you are able to navigate to the details for each application by clicking on the application in the diagram. Once on the details page for an application you are able to see the list of connected application instances, list of handled commands, list of handled queries, and running event processors

Running our business

Populate Inventory of Bikes

In order to begin offering our bike rental service we will need an inventory of bikes. To do this, navigate to the requests.http file, find the section with the header ### Generate bikes and executing the http POST command shown. This will give you an inventory of bikes which you can verify by executing the http command found in the### List all section of requests.http file.

Generate Bike Rentals

Now that your inventory is in place it is time to make some money!! To simulate all the steps of a rental and return (request a bike, completing payment, unlocking, and finally returning) we can execute the http command found at the header ### Generate Rentals of the of requests.http file.

Evolving Rental Application monolith to microservices

Great news! The Axoniq World Wide Bike Rental Service is renting bikes faster than we can buy them! As a result our Rental Application is experiencing some scalability issues. To handle this increase in volume on our application it has been determined that we need to break out the parts of the Rental Application each in to their own service. Our updated architecture now looks like the following...

To make this happen run the create-microservices.sh script to copy the necessary files into the pre-defined services in the project. Once the script is complete, you must stop the running RentalApplication app (port conflict), and then run the new services RentalCommandApplication, RentalPaymentSagaApplication, RentalQueryApplication, and UserInterfaceApplication.

This allows us to run each aspect of our Rental domain as an independent service with no functional changes to the code base. Our initial approach of using features in Axon Framework such as Command Gateway and Query Gateway have provided us with location independence between our components. We are now able to evolve and scale each component as necessary to handle the increased load of our ever growing bike rental business.

Monitoring our Axon Framework and Axon Server based services

To be able to understand the performance of our services, we can use the Axoniq Console. Using Axoniq Console we can register each of our microservices, check on performance command handling within our Aggregates (Bike and Payment), query handling performance, and event processors as well.