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eventuate-tram / eventuate-tram-core

Transactional messaging for microservices
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= An Eventuate project

image::https://eventuate.io/i/logo.gif[]

This project is part of http://eventuate.io[Eventuate], which is a microservices collaboration platform.

= Eventuate Tram (Transactional Messaging) platform

[cols="a,a"] |=== | Spring/Micronaut | image::https://img.shields.io/maven-central/v/io.eventuate.tram.core/eventuate-tram-bom[link="https://search.maven.org/artifact/io.eventuate.tram.core/eventuate-tram-bom"] | Quarkus | image::https://img.shields.io/maven-central/v/io.eventuate.tram.core/eventuate-tram-quarkus-bom[link="https://search.maven.org/artifact/io.eventuate.tram.core/eventuate-tram-bom"] |===

Eventuate Tram is a platform that solves the distributed data management problems inherent in a http://microservices.io/patterns/microservices.html[microservice architecture].

It is described in more detail in my book https://www.manning.com/books/microservice-patterns[Microservice Patterns] and the http://eventuate.io/tram/gettingstarted.html[getting started guide].

== Key benefits of Eventuate Tram

++++

Maintain data consistency using sagas

Implement commands that update data in multiple microservices by using Sagas, which are sequences of local transactions coordinated using messages

Implement queries using CQRS

Implement queries that retrieve data from multiple services by using CQRS views, which are easily queryable replicas maintained using events

Communicate using transactional messaging

Reliably send and receive messages and events as part of a database transaction by using the Transactional Outbox pattern

++++

== How it works

Eventuate Tram provides several messaging abstractions:

Eventuate Tram messaging implements the http://microservices.io/patterns/data/application-events.html[Transactional Outbox pattern]. An message producer inserts events into an OUTBOX table as part of the ACID transaction that updates data, such as JPA entities. A separate message relay (a.k.a. Eventuate CDC service) publishes messages to the message broker.

image::https://raw.githubusercontent.com/eventuate-tram/eventuate-tram-core/master/ReliablePublication.png[]

The Eventuate CDC service works in one of two ways:

== Supported technologies

Languages:

Databases:

Message brokers:

== Getting started

Please see the http://eventuate.io/tram/gettingstarted.html[getting started guide].

== Example applications

There are numerous example applications:

== Got questions?

Don't hesitate to create an issue or see

== Need support?

Take a look at the http://eventuate.io/support.html[available paid support] options.

== Transactional messaging

Send a message using MessageProducer:

public interface MessageProducer {
  void send(String destination, Message message);
}

Receive messages using:

public interface MessageConsumer {
  void subscribe(String subscriberId, Set<String> channels, MessageHandler handler);
}

See this example of https://github.com/eventuate-tram/eventuate-tram-core-examples-basic/blob/master/eventuate-tram-examples-common/src/main/java/io/eventuate/tram/examples/basic/messages/AbstractTramMessageTest.java[transactional messaging].

=== Transactional domain events

The domain event package builds on the core APIs.

Publish domain events using the DomainEventPublisher interface:

public interface DomainEventPublisher {

  void publish(String aggregateType, Object aggregateId, List<DomainEvent> domainEvents);
  ...

Subscribe to domain events using a DomainEventDispatcher:

public class DomainEventDispatcher {
    public DomainEventDispatcher(String eventDispatcherId,
                DomainEventHandlers eventHandlers,
                ...) {
...
}

Handle the events using DomainEventHandlers:

public class RestaurantOrderEventConsumer {

  public DomainEventHandlers domainEventHandlers() {
    return DomainEventHandlersBuilder
            .forAggregateType("net.chrisrichardson.ftgo.restaurantservice.Restaurant")
            .onEvent(RestaurantMenuRevised.class, this::reviseMenu)
            .build();
  }

  public void reviseMenu(DomainEventEnvelope<RestaurantMenuRevised> de) {

See this example of https://github.com/eventuate-tram/eventuate-tram-core-examples-basic/blob/master/eventuate-tram-examples-common/src/main/java/io/eventuate/tram/examples/basic/events/AbstractTramEventTest.java[transaction events].

== Transactional commands

Transaction commands are implemented using transactional messaging.

Send a command using a CommandProducer:

public interface CommandProducer {
  String send(String channel, Command command, String replyTo, Map<String, String> headers);
  ...
}

Subscribe to commands using a CommandDispatcher:

public class CommandDispatcher {

  public CommandDispatcher(String commandDispatcherId,
           CommandHandlers commandHandlers) {
  ...
}

Handle commands and send a reply using CommandHandlers:

public class OrderCommandHandlers {

  public CommandHandlers commandHandlers() {
    return CommandHandlersBuilder
          .fromChannel("orderService")
          .onMessage(ApproveOrderCommand.class, this::approveOrder)
          ...
          .build();
  }

  public Message approveOrder(CommandMessage<ApproveOrderCommand> cm) {
    ApproveOrderCommand command = cm.getCommand();
    ...
  }

See this example of https://github.com/eventuate-tram/eventuate-tram-core-examples-basic/blob/master/eventuate-tram-examples-common/src/main/java/io/eventuate/tram/examples/basic/commands/AbstractTramCommandTest.java[transactional commands].

== Maven/Gradle artifacts

The artifacts are in https://bintray.com/eventuateio-oss/eventuate-maven-release/eventuate-tram[JCenter]. The latest version is:

[cols="5%,20%a"] |=== | RC | image::https://api.bintray.com/packages/eventuateio-oss/eventuate-maven-rc/eventuate-tram/images/download.svg[link="https://bintray.com/eventuateio-oss/eventuate-maven-rc/eventuate-tram/_latestVersion"] | Release | image::https://api.bintray.com/packages/eventuateio-oss/eventuate-maven-release/eventuate-tram/images/download.svg[link="https://bintray.com/eventuateio-oss/eventuate-maven-release/eventuate-tram/_latestVersion"] |===

There are the following API artifacts:

There are the following 'implementation' artifacts:

== Running the CDC service

In addition to a database and message broker, you will need to run the Eventuate Tram CDC service. It reads events inserted into the database and publishes them to the message broker. It is written using Spring Boot. The easiest way to run this service during development is to use Docker Compose. The https://github.com/eventuate-tram/eventuate-tram-core-examples-basic[Eventuate Tram Code Basic examples] project has an example docker-compose.yml file.

== Contributing

Contributions are welcome.

Please sign a https://chrisrichardson.net/legal/[contributor license agreement].