Event Sourcing and CQRS on the JVM

The objective of this project was to evaluate one of the available solutions in the JVM ecosystem for implementing an application using the Event Sourcing and CQRS patterns. It consists of two modules - axon and gatling. The former is the implementation of aforementioned application using Axon Framework, the latter contains Gatling load tests, created to assess the scalability of the system. The axon module contains the implementation of the main components of the application - the command model (hotel-booking-command submodule), the query model (hotel-booking-query submodule) and the API gateway (gateway submodule).

The domain of the system is based on the example used in the following blog post: https://eventmodeling.org/posts/what-is-event-modeling/.

How to run the application

Firstly, to start all infrastructural components of the system, execute docker compose up -d command on the docker-compose.yml file located in axon directory. You can also use docker compose --profile 2-instances up -d or docker compose --profile 3-instances up -d to run 2 or 3 instances of read model database respectively.

The project contains preconfigured run configurations, located in the .run directory, which should be automatically detected by your IDE. They enable to run 1, 2 or 3 instances of command and query side Spring Boot applications. Alternatively, you can use following Gradle Wrapper commands:

• Gateway

  ./gradlew :axon:gateway:bootRun
  

• Command side

  ./gradlew :axon:hotel-booking-command:bootRun
  

  For second instance:

  ./gradlew :axon:hotel-booking-command:bootRun --args='--server.port=8082'
  

• Query side

  ./gradlew :axon:hotel-booking-query:bootRun
  

  For second instance:

  ./gradlew :axon:hotel-booking-query:bootRun --args='--server.port=8182 --spring.data.mongodb.port=27018'
  

How to run the load tests

After starting the application, you can run the load tests by executing one of the following Gradle Wrapper commands:

• For command side

  ./gradlew :gatling:gatlingRun-simulations.HotelBookingCommandSimulation
  

• For query side

  Firstly (to populate the event store):

  ./gradlew :gatling:gatlingRun-simulations.GenerateAggregatesSimulation
  

  Then:

  ./gradlew :gatling:gatlingRun-simulations.HotelBookingQuerySimulation