axon-springboot-websocket

The goal of this project is to play with Axon. For this, we will implement a food-ordering app that consists of three Spring Boot applications: customer-service, restaurant-service, and food-ordering-service. These services were implemented with CQRS and Event Sourcing in mind. To achieve this, we used the Axon Framework. The three services are connected to axon-server, which is the Event Store and Message Routing solution used.

Proof-of-Concepts & Articles

On ivangfr.github.io, I have compiled my Proof-of-Concepts (PoCs) and articles. You can easily search for the technology you are interested in by using the filter. Who knows, perhaps I have already implemented a PoC or written an article about what you are looking for.

Project Diagram

Applications

• customer-service

  Spring Boot application that exposes a REST API to manage Customers. It also has a UI implemented using JavaScript, jQuery, and Semantic UI.

  

  customer-service was implemented using the Axon Framework. Every time a customer is added, updated, or deleted, the service emits the respective event, i.e., CustomerAddedEvent, CustomerUpdatedEvent, or CustomerDeletedEvent.

  customer-service uses MySQL to store customer data. Additionally, it listens to order events, collects the order information that it needs, and stores them in an order table present in its own database, so that it doesn't need to call another service to get this information.

• restaurant-service

  Spring Boot application that exposes a REST API to manage Restaurants. It also has a UI implemented using JavaScript, jQuery, and Semantic UI.

  

  restaurant-service was implemented using the Axon Framework. Every time a restaurant is added, updated, or deleted, the service emits the respective event, i.e., RestaurantAddedEvent, RestaurantUpdatedEvent, or RestaurantDeletedEvent. The same applies to the restaurant dishes, whose events are: RestaurantDishAddedEvent, RestaurantDishUpdatedEvent, or RestaurantDishDeletedEvent.

  restaurant-service uses PostgreSQL to store restaurant/dish data. Additionally, it listens to order events, collects the order information that it needs, and stores them in an order table present in its own database, so that it doesn't need to call another service to get this information.

• food-ordering-service

  Spring Boot application that exposes a REST API to manage Orders. It has a UI implemented using JavaScript, jQuery, and Semantic UI.

  

  food-ordering-service was implemented using the Axon Framework. Every time an order is created, the service emits the respective event, i.e., OrderCreatedEvent.

  food-ordering-service uses MongoDB to store order data. Additionally, it listens to customer and restaurant/dish events, collects the information that it needs, and stores them in a customer or restaurant/dish table present in its own database, so that it doesn't need to call another service to get this information.

• axon-event-commons

  Maven project where all events mentioned above are defined. It generates a JAR file that is added as a dependency in the pom.xml of customer-service, restaurant-service, and food-ordering-service.

Prerequisites

• Java 17 or higher;
• A containerization tool (e.g., Docker, Podman, etc.)

Start Environment

• Open a terminal and inside the axon-springboot-websocket root folder run:

  docker compose up -d

• Wait for Docker containers to be up and running. To check it, run:

  docker ps -a

Running applications with Maven

Inside the axon-springboot-websocket root folder, run the following commands in different terminals:

• axon-event-commons

  ./mvnw clean install --projects axon-event-commons

• customer-service

  ./mvnw clean spring-boot:run --projects customer-service -Dspring-boot.run.jvmArguments="-Dserver.port=9080"

• restaurant-service

  ./mvnw clean spring-boot:run --projects restaurant-service -Dspring-boot.run.jvmArguments="-Dserver.port=9081"

• food-ordering-service

  ./mvnw clean spring-boot:run --projects food-ordering-service -Dspring-boot.run.jvmArguments="-Dserver.port=9082"

Running applications as Docker containers

• Build Docker images

  • In a terminal, make sure you are in the axon-springboot-websocket root folder;
  • Run the following script to build the Docker images:

    ./build-docker-images.sh

• Environment Variables

  • customer-service

    Environment Variable	Description
    MYSQL_HOST	Specify the host of the MySQL database to use (default localhost)
    MYSQL_PORT	Specify the port of the MySQL database to use (default 3306)
    AXON_SERVER_HOST	Specify the host of the Axon Server to use (default localhost)
    AXON_SERVER_PORT	Specify the port of the Axon Server to use (default 8124)

  • restaurant-service

    Environment Variable	Description
    POSTGRES_HOST	Specify the host of the Postgres database to use (default localhost)
    POSTGRES_PORT	Specify the port of the Postgres database to use (default 5432)
    AXON_SERVER_HOST	Specify the host of the Axon Server to use (default localhost)
    AXON_SERVER_PORT	Specify the port of the Axon Server to use (default 8124)

  • food-ordering-service

    Environment Variable	Description
    MONGODB_HOST	Specify the host of the Mongo database to use (default localhost)
    MONGODB_PORT	Specify the port of the Mongo database to use (default 27017)
    AXON_SERVER_HOST	Specify the host of the Axon Server to use (default localhost)
    AXON_SERVER_PORT	Specify the port of the Axon Server to use (default 8124)

• Start Docker containers

  • In a terminal, make sure you are inside the axon-springboot-websocket root folder;
  • Run the following command:

    ./start-apps.sh

Application URLs

Application	URL	Swagger
customer-service	http://localhost:9080	http://localhost:9080/swagger-ui.html
restaurant-service	http://localhost:9081	http://localhost:9081/swagger-ui.html
food-ordering-service	http://localhost:9082	http://localhost:9082/swagger-ui.html

Demo

The GIF below shows a user creating a customer in the customer-service UI. Then, in the restaurant-service UI, they create a restaurant and add a dish. Finally, using the food-ordering-service UI, they submit an order using the customer and restaurant/dish created. Note that as soon as a customer or restaurant/dish is created, an event is sent, and the consumer of this event updates its UI in real-time using WebSockets.

Useful Commands & Links

• Axon Server

  The Axon Server dashboard can be accessed at http://localhost:8024

  

• MySQL

  docker exec -it -e MYSQL_PWD=secret mysql mysql -uroot --database customerdb
  
  SELECT * FROM customers;
  SELECT * FROM orders;

  Type exit to exit

• PostgreSQL

  docker exec -it postgres psql -U postgres -d restaurantdb
  
  SELECT * FROM restaurants;
  SELECT * FROM dishes;
  SELECT * FROM orders;

  Type \q to exit

• MongoDB

  docker exec -it mongodb mongo foodorderingdb
  
  db.customers.find()
  db.restaurants.find()
  db.orders.find()

  Type exit to exit

Shutdown

• To stop applications:
  • If you start them with Maven, go to the terminals where they are running and press Ctrl+C;
  • If you start them as Docker containers, make sure you are inside the axon-springboot-websocket root folder and run the following script:

    ./stop-apps.sh

• To stop and remove docker compose containers, network, and volumes, go to a terminal and, inside the axon-springboot-websocket root folder, run the command below:

  docker compose down -v

Cleanup

To remove the docker images created by this project, go to a terminal and, inside the axon-springboot-websocket root folder, run the following script:

./remove-docker-images.sh

References

• https://sgitario.github.io/axon-by-example/
• https://blog.nebrass.fr/playing-with-cqrs-and-event-sourcing-in-spring-boot-and-axon/