istio.io/content/help/faq/distributed-tracing/how-mixer-based-tracing-works.md

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How does Mixer-based tracing work?	12

For Mixer-based tracing integrations, Mixer (addressed through the istio-telemetry service) provides the integration with tracing backends. The Mixer integration allows additional levels of operator control of the distributed tracing, including fine-grained selection of the data included in trace spans. It also provides the ability to send traces to backends not supported by Envoy directly.

For Mixer-based integrations, Envoy:

• generates request IDs and trace headers (i.e. X-B3-TraceId) for requests as they flow through the proxy
• calls Mixer for general asynchronous telemetry reporting
• forwards the trace headers to the proxied application

Mixer:

• generates trace spans for each request based on operator-supplied configuration
• sends the generated trace spans to the operator-designated tracing backends

The Stackdriver tracing integration with Istio is one example of a tracing integration via Mixer.