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RUMM-1579 Inject sampling headers to instrumented requests #575

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ncreated
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@ncreated ncreated commented Aug 27, 2021

What and why?

🐞 This PR aligns our trace propagation logic with "How are RUM resources linked to traces?" doc by adding two more headers to instrumented requests:

x-datadog-sampling-priority: 1 
x-datadog-sampled: 1

As reported in #572, lack of these headers may lead to not connecting mobile and backend trace in distributed tracing. The issue is hard to reproduce in our own infra, as we seem to overwrite sampling rules. In this fix I'm basing on docs, customer observation and my research on other DD SDKs implementation (including browser-sdk that respects those headers).

This PR targets the 1.7.0-beta4 branch made for next release. Once merged, I will raise another PR to update master with this fix from 1.7.0-beta4.

How?

I added these 2 headers to HTTPHeadersWriter which is used internally for headers injection. I did necessary update to unit tests and integration tests (both for Swift URLSession and Obj-c NSURLSession auto-instrumentation in RUM and Tracing).

Review checklist

  • Feature or bugfix MUST have appropriate tests (unit, integration)
  • Make sure each commit and the PR mention the Issue number or JIRA reference

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@maxep maxep left a comment

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Nice work 👏 I have a non-blocking question.

@ncreated ncreated merged commit cbd2249 into release/1.7.0-beta4 Aug 31, 2021
@ncreated ncreated deleted the ncreated/RUMM-1579-inject-sampling-headers-when-propagating-trace branch August 31, 2021 14:33
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3 participants