To enable Long Running Actions add the following dependency to your project’s pom.xml (see Managing Dependencies).

<dependency>
  <groupId>io.helidon.microprofile.lra</groupId>
  <artifactId>helidon-microprofile-lra</artifactId>
</dependency>
<!-- Support for Narayana coordinator -->
<dependency>
  <groupId>io.helidon.lra</groupId>
  <artifactId>helidon-lra-coordinator-narayana-client</artifactId>
</dependency>

Distributed transactions for microservices are known as SAGA design patterns and are defined by the Micro Profile Long Running Actions specification. Unlike well known XA protocol, LRA is asynchronous and therefore much more scalable. Every LRA JAX-RS resource (participant) defines endpoints to be invoked when transaction needs to be completed or compensated.

LRA transactions need to be coordinated over REST API by the LRA coordinator. Coordinator keeps track of all transactions and calls the @Compensate or @Complete endpoints for all participants involved in the particular transaction. LRA transaction is first started, then joined by participant. Participant reports the successful finish of transaction by calling complete. Coordinator then calls the JAX-RS complete endpoint that was registered during the join of each participant. As the completed or compensated participants don’t have to be on same instance, the whole architecture is highly scalable.

In case of error during the LRA transaction, participant reports cancel of LRA to coordinator. Coordinator calls compensate on all the joined participants.

When participant joins the LRA with timeout defined @LRA(value = LRA.Type.REQUIRES_NEW, timeLimit = 5, timeUnit = ChronoUnit.MINUTES), coordinator compensate if timeout occurs before close is reported by participants.

Example

@PUT
@LRA(LRA.Type.REQUIRES_NEW) 
@Path("start-example")
public Response startExample(@HeaderParam(LRA_HTTP_CONTEXT_HEADER) URI lraId, 
                             String data) {
    if (data.contains("BOOM")) {
        throw new RuntimeException("BOOM 💥"); 
    }

    LOGGER.info("Data " + data + " processed 🏭");
    return Response.ok().build(); 
}

@PUT
@Complete 
@Path("complete-example")
public Response completeExample(@HeaderParam(LRA_HTTP_CONTEXT_HEADER) URI lraId) {
    LOGGER.log(Level.INFO, "LRA id: {0} completed 🎉", lraId);
    return LRAResponse.completed();
}

@PUT
@Compensate 
@Path("compensate-example")
public Response compensateExample(@HeaderParam(LRA_HTTP_CONTEXT_HEADER) URI lraId) {
    LOGGER.log(Level.SEVERE, "LRA id: {0} compensated 🦺", lraId);
    return LRAResponse.compensated();
}

Configuration

mp.lra:
  coordinator.url: http://localhost:8070/lra-coordinator 
  propagation.active: true 
  participant.url: http://coordinator.visibe.host:80/awsomeapp