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Trace ID leakage in reactive Kafka consumer concatMap operations

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
java, kafka
Domain
distributed-systems, observability-sre

Research direction

Start with the linked reactive-kafka-consumer reproduction and run it with dd-java-agent versions 1.43.0 and 1.53.0. Compare trace IDs inside sequential concatMap processing with the outer chain and with flatMap. Done means each consumed message keeps its own Kafka-header trace ID throughout concatMap processing, without manual context management.

Written by the indexing model from the issue text.

Description

type: bug report
Tracer Version(s)

1.43.0, 1.53.0

Java Version(s)

17.0.15

JVM Vendor

Oracle JDK

Bug Report

When using dd-java-agent's automatic instrumentation with reactor-kafka, trace IDs from the first consumed Kafka message incorrectly leak into subsequent messages within concatMap operators. No manual span creation or context management is being used - this occurs purely with automatic instrumentation.

Actual Behavior

  1. First message: Trace ID is correctly set (e.g., trace_id=123)
  2. Second message: The outer reactive chain has a new trace ID (e.g., trace_id=456) - this is correct
    Operations inside concatMap still show the first message's trace ID (trace_id=123) - here expected trace_id=456

Issue does not occur with flatMap - only with concatMap (sequential processing)

Is manual context propagation required for concatMap scenarios, or is this a bug in automatic instrumentation?

Expected Behavior
  1. First message: Trace ID is correctly extracted from Kafka headers (e.g., trace_id=123) and maintained throughout the processing chain
  2. Second and subsequent messages: Each message's trace ID from its Kafka headers is properly extracted and maintained throughout the entire chain processing, independent of previous messages
Reproduction Code

https://github.com/faent/reactive-kafka-consumer/tree/main

Dominant language
Java
Stars
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Forks
361
Avg merge
3d 20h
Merged PRs (30d)
173

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