Todo list tutorial
It’s challenging for micro-service API to update data (e.g. a Domain-Driven design aggregate) and publish a message, such as a domain event. The traditional approach of using 2PC/JTA isn’t a good fit for micro-service applications.
The light-tram-4j framework implements an alternative mechanism based on the Application Events pattern.
When an application creates or updates data, as part of that ACID transaction, it inserts an event into a MESSAGE table. A separate process publishes those events to a message broker, such as Apache Kafka.
About the Todo list application
The Todo List application, which lets users maintain a todo list, is the end-to-end POC application for the light-tram-4j framework.
It shows how to use light-tram-4j to:
reliably publish domain events as part of a database transaction that updates an aggregate.
consume domain events to update a CQRS view
When a user creates or updates a todo on the command side service, the application publishes a domain event. An event handler on the query side service, subscribes to those events and updates an ElasticSearch-based CQRS view.
Todo list architecture
The Todo List application is built using
Java JDK 11
The application persists the Todo entity in MySQL. It also maintains a materialized view of the data in ElasticSearch.
How it works
The Todo application uses the light-tram-4j framework to publish and consume domain events.
TodoCommandService persists the todo entity to the local data store and publishes an event when it creates, updates, or deletes a Todo item. It uses the DomainEventPublisher, which is implemented by the light-tram-4j framework.
light-tram-4j cdc server will get the published events from MESSAGE table and publish to Kafka message broker.
TodoQueryService application uses TodoEventConsumer defines the event handlers, which updates Elasticsearch to maintain a materialize view.
The following steps are included in the tutorial and there are simple steps in README.md. As we have two implementations, single-module and multi-module to represent monolithic and microservices, we are going to focus on the multi-module project for this tutorial.