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Trace Tags Propagation in Distributed Traces #2260
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## master #2260 +/- ##
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Coverage 98.33% 98.33%
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Files 1100 1102 +2
Lines 58334 58613 +279
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+ Hits 57361 57638 +277
- Misses 973 975 +2
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Pretty big, but good to see this ready to go! Thanks for your hard work, and patience with reviews on this one.
If you think it would be helpful, I would encourage sanity-testing a pre-release build in some kind of controlled environment. But that shouldn't block a merge at this point.
This implements the propagation of Datadog-specific trace tags across a distributed trace's lifecycle.
Trace tags starting with the string
_dd.p.
are considered Datadog distributed tags, are are propagated through the newx-datadog-tags
header.The
x-datadog-tags
header is consumed from upstream calls, if present, and inject into downstream calls when present.The first value for a distributed tag is
_dd.p.dm
: Sampling Decision Maker. This tag represents what mechanism was used to make a sampling decision.When the sampling decision comes from an upstream context,
ddtrace
propagates that value downstream, as well as setting it as a trace-level tag. This tag will be flushed with trace payload.When the sampling decision is made in the instrumented Ruby application, the value of
_dd.p.dm
is populated locally and propagated downstream.