Service A calls B over HTTP and also sends it jobs through a queue, but B's spans show up as separate traces instead of under A's. What is the likely cause?

Options

• ✗ The clocks of A and B are out of sync
• ✗ B's sampling rate is too low
• ✓ A does not pass the trace context (such as the W3C traceparent header) with its calls and messages Correct
• ✗ B writes its logs as plain text

Why

Every hop must carry the trace id and parent span id: HTTP and gRPC headers, and message headers or attributes for queues. Instrumentation libraries (OpenTelemetry) do it for supported clients; hand-made HTTP clients and queue producers are where the chain usually breaks.

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