Context propagation

[pavolloffay]

I am creating this based on smallrye/smallrye-reactive-messaging#214

Allow in-process context propagation between handlers. The API can be used by users to propagate any objects between handlers, but It is also necessary for tracing to propagate span context object to be able to link spans in handlers:

@Incoming("data-processor-in")
@Outgoing("data-processor-out")
public CompletionStage<KafkaMessage<String, String>> send(KafkaMessage<String, String> message) {
  CompletableFuture<KafkaMessage<String, String>> future = new CompletableFuture<>();
  future.complete(KafkaMessage.ofAndTraced(message.getKey(), message.getPayload().toUpperCase(), message.getSpan()));
  return future;
}

links span from data-processor-in to data-processor-out topics.

Two solutions have been already discussed:

• Add context object (Map<String, Object>)to the message class. Q: How would user get the context? The implementation would have to provide an SPI to initialize TLS.
• Integrate with https://github.com/eclipse/microprofile-context-propagation - activate TLS for every user-defined handlers. The correct TLS has to be set

Once the context propagation is in place we could provide tracing for underlying messaging platforms but in addition to also model invocations of the handlers themselves.

Other

Related to #2?

[Emily-Jiang]

I think it is much better to integrate with context propagation as it was created to server the purpose of this spec and Fault Tolerance.

[pilhuhn]

Where do we stand here?
I think it is important to solve that rather sooner than later as any (reactive) messaging things are becoming more popular these days.

[cescoffier]

SmallRye includes in its last version metadata propagation (metadata associated with messages) and supports context propagation (capture of the context and propagation to the subscriber).

[Emily-Jiang]

See See https://smallrye.io/smallrye-reactive-messaging/smallrye-reactive-messaging/2/concepts.html#messages