Explain Trace Propagation and W3C TraceContext.

Example

A user request travels from a frontend → API → database → payment service. With TraceContext, the same traceparent ID follows the request, making it easy to pinpoint a slow payment service call.

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Why Is It Important

• Enables end-to-end observability
• Reduces mean time to resolution (MTTR)
• Ensures vendor neutrality across tracing tools
• Helps meet SLAs/SLOs by tracking latency sources

Interview Tips

• Start by defining propagation and TraceContext.
• Mention the two headers: traceparent and tracestate.
• Give an example flow.
• Add nuance: baggage handling, async jobs, and proxies/CDNs.

Trade-offs

• Pros: portable context, reduced debugging time, ecosystem standardization
• Cons: overhead in headers, complexity in async systems, potential privacy risks if baggage misused

Pitfalls

• Forgetting to forward headers in async consumers
• Dropping headers at load balancers/CDNs
• Starting new traces instead of continuing existing ones
• Adding sensitive data to tracestate or baggage