Use Cases for LRA

Question

I am attempting to accomplish something along these lines with Quarkus, and Naryana:

• client calls service to start a process that takes a while: /lra/start
  • This call sets off an LRA, and returns an LRA id used to track the status of the action
• client can keep polling some endpoint to determine status
• service eventually finishes and marks the action done through the coordinator
• client sees that the action has completed, is given the result or makes another request to get that result

Is this a valid use case? Am I visualizing the correct way this tool can work? Based on how the linked guide reads, it seems that the endpoints are more of a passthrough to the coordinator, notifying it that we start and end an LRA. Is there a more programmatic way to interact with the coordinator?

Answer 1

Yes, it might be a valid use case, but in every case please read the MicroProfile LRA specification - https://github.com/eclipse/microprofile-lra.

The idea you describe is more or less one LRA participant executing in a new LRA and polling the status of this execution. This is not totally what the LRA is intended for, but surely can be used this way.

The main idea of LRA is the composition of distributed transactions based on the saga pattern. Basically, the point is to coordinate multiple services to achieve consistent results with an eventual consistency guarantee. So you see that the main benefit arises when you can propagate LRA through different services that either all complete their actions or all of their compensation callbacks will be called in case of failures (and, of course, only for the services that executed their actions in the first place). Here is also an example with the LRA propagation https://github.com/xstefank/quarkus-lra-trip-example.

EDIT: Sorry, I forgot to add the programmatic API that allows same interactions as annotations - https://github.com/jbosstm/narayana/blob/master/rts/lra/client/src/main/java/io/narayana/lra/client/NarayanaLRAClient.java. However, note that is not in the specification and is only specific to Narayana.