istio.io/content/help/faq/distributed-tracing/no-tracing.md

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Why are my requests not being traced?	30

Since Istio 1.0.3, the default sampling rate for tracing has been reduced to 1% when installing Istio using the Helm chart. This means that only 1 out of 100 trace instances captured by Istio will be reported to the tracing backend. The sampling rate in the istio-demo.yaml is still set to 100%. See this section for more information on how to set the sampling rate.

If you still do not see any trace data, please confirm that your ports conform to the Istio port naming conventions and that the appropriate container port is exposed (via pod spec, for example) to enable traffic capture by the sidecar proxy (Envoy).