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The Datadog APM tracer supports extraction and injection of B3 and W3C Trace Context headers for distributed tracing.

Distributed headers injection and extraction is controlled by configuring injection and extraction styles. Supported styles are: tracecontext, datadog, b3multi and b3 single header.

  • Configure injection styles using the DD_TRACE_PROPAGATION_STYLE_INJECT=tracecontext,b3mutli environment variable.
  • Configure extraction styles using the DD_TRACE_PROPAGATION_STYLE_EXTRACT=tracecontext,b3multi environment variable.
  • Configure both injection and extraction styles using the DD_TRACE_PROPAGATION_STYLE=tracecontext,b3multi environment variable.

The values of these environment variables are comma-separated lists of header styles enabled for injection or extraction. By default, the datadog,tracecontext styles are enabled.

To disable trace context propagation, set the value of the environment variables to none.

  • Disable injection styles using the DD_TRACE_PROPAGATION_STYLE_INJECT=none environment variable.
  • Disable extraction styles using the DD_TRACE_PROPAGATION_STYLE_EXTRACT=none environment variable.
  • Disable all trace context propagation (both inject and extract) using the DD_TRACE_PROPAGATION_STYLE=none environment variable.

If multiple environment variables are set, DD_TRACE_PROPAGATION_STYLE_INJECT and DD_TRACE_PROPAGATION_STYLE_EXTRACT override any value provided in DD_TRACE_PROPAGATION_STYLE.

When multiple extraction styles are enabled, the extraction attempt is done in the order those styles are configured using the first successful extracted value. If valid trace contexts are found later, they are terminated and appended as span links. Additionally, if the tracecontext style is enabled, W3C Tracestate is propagated if W3C Traceparent matches the extracted context.

Further Reading