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Headers extraction and injection

Datadog APM tracer supports B3 and W3C Trace Context header extraction and injection for distributed tracing.

Distributed headers injection and extraction is controlled by configuring injection and extraction styles. The following styles are supported:

  • Datadog: Datadog
  • B3 Multi Header: b3multi
  • B3 Single Header: b3
  • W3C Trace Context: tracecontext
  • No-op: none

Injection styles can be configured using:

  • Environment Variable: DD_TRACE_PROPAGATION_STYLE_INJECT=Datadog,b3

The value of the environment variable is a comma-separated list of header styles that are enabled for injection. The default setting is Datadog,tracecontext.

Extraction styles can be configured using:

  • Environment Variable: DD_TRACE_PROPAGATION_STYLE_EXTRACT=Datadog,b3

The value of the environment variable is a comma-separated list of header styles that are enabled for extraction.

If multiple extraction styles are enabled extraction attempt is done on the order those styles are configured and first successful extracted value is used.

The default extraction styles are, in order, Datadog, b3multi, b3, and tracecontext.

You can also enable or disable the use of these formats in code by using Datadog.configure:

Datadog.configure do |c|
  # List of header formats that should be extracted
  c.tracing.distributed_tracing.propagation_extract_style = [ 'tracecontext', 'Datadog', 'b3' ]

  # List of header formats that should be injected
  c.tracing.distributed_tracing.propagation_inject_style = [ 'tracecontext', 'Datadog' ]
end

For more information about trace context propagation configuration, read the Distributed Tracing section in the Ruby Tracing Library Configuration docs.

Further Reading