Propagate and Observation from Reactive context #3999
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To propagate an `Observation` from reactive stream (e.g. WebFlux) we have to capture its context and set it into the current thread scope. * Add a `io.micrometer:context-propagation` dependency to support reactive context propagation * Populate a `parentObservation` in the `IntegrationObservation.PRODUCER.observation()` since it is not available for tracing on `Observation.onStart()`. Might be tentative until upcoming fix in Micrometer Observation * Populate from reactive context in the `WebFluxInboundEndpoint` where we use just `send()` operation downstream * Populate from reactive context in the `MessagingGatewaySupport` where we use `send()` operation downstream or `FluxMessageChannel.subscribeTo()` * Use `contextCapture()` in the `FluxMessageChannel` to gather a `ThreadLocal` info into a Reactor context and then set back to `ThreadLocal` in the `transformDeferredContextual()` which really happens on a different thread * Verify a trace propagation from WebFlux to an integration flow via Brave instrumentation in the `WebFluxObservationPropagationTests`
garyrussell
reviewed
Feb 1, 2023
| .flatMap(replyMessage -> populateResponse(exchange, replyMessage)); | ||
| } | ||
| else { | ||
| var scope = ContextSnapshot.setAllThreadLocalsFrom(contextView); |
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Why is this not required in the send/receive case?
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It is covered by the MessagingGatewaySupport change in this PR.
We need such an action only when we lose a reactive scope.
This send() returns nothing, but sendAndReceiveMessageReactive() returns a Mono where respective context is still present. Therefore we have to repeat a set to ThreadLocal over there where we lose the reactive stream context again.
That's why I have those separate tests in this PR.
NOTE: The RSocket support will work as well just because we have a fix in the MessagingGatewaySupport and it does not use a plain send().
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To propagate an
Observationfrom reactive stream (e.g. WebFlux) we have to capture its context and set it into the current thread scope.io.micrometer:context-propagationdependency to support reactive context propagationparentObservationin theIntegrationObservation.PRODUCER.observation()since it is not available for tracing onObservation.onStart(). Might be tentative until upcoming fix in Micrometer ObservationWebFluxInboundEndpointwhere we use justsend()operation downstreamMessagingGatewaySupportwhere we usesend()operation downstream orFluxMessageChannel.subscribeTo()contextCapture()in theFluxMessageChannelto gather aThreadLocalinfo into a Reactor context and then set back toThreadLocalin thetransformDeferredContextual()which really happens on a different threadWebFluxObservationPropagationTests