[NO-TICKET] Profiling: Add setting to use system dns

[ivoanjo]

What does this PR do?

This PR introduces a new profiler advanced setting experimental_use_system_dns (controlled via DD_PROFILING_EXPERIMENTAL_USE_SYSTEM_DNS environment variable) that allows falling back to the system DNS resolver instead of using libdatadog's built-in resolver.

The setting defaults to false, meaning that by default the libdatadog built-in DNS resolver is used.

Motivation:

Using system DNS has been flagged as problematic in e.g. #3815 and thus avoiding it by default for profiling will remove one of the potential sources for issues.

Change log entry

Yes. Profiling: Add setting to use system dns

Additional Notes:

See DataDog/libdatadog#1558 for more details on the libdatadog side of this feature.

How to test the change?

This change includes test coverage.

[datadog-datadog-prod-us1-2]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

🎯 Code Coverage (details)
• Patch Coverage: 87.50%
• Overall Coverage: 95.11% (-0.02%)

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 3cb9136 | Docs | Datadog PR Page | Was this helpful? React with 👍/👎 or give us feedback!}

[pr-commenter]

Benchmarks

Benchmark execution time: 2026-03-06 15:23:59

Comparing candidate commit 3cb9136 in PR branch ivoanjo/system-dns-config with baseline commit b60e998 in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 46 metrics, 0 unstable metrics.

Explanation

This is an A/B test comparing a candidate commit's performance against that of a baseline commit. Performance changes are noted in the tables below as:

• 🟩 = significantly better candidate vs. baseline
• 🟥 = significantly worse candidate vs. baseline

We compute a confidence interval (CI) over the relative difference of means between metrics from the candidate and baseline commits, considering the baseline as the reference.

If the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD), the change is considered significant.

Feel free to reach out to #apm-benchmarking-platform on Slack if you have any questions.

More details about the CI and significant changes

You can imagine this CI as a range of values that is likely to contain the true difference of means between the candidate and baseline commits.

CIs of the difference of means are often centered around 0%, because often changes are not that big:

---------------------------------(------|---^--------)-------------------------------->
                              -0.6%    0%  0.3%     +1.2%
                                 |          |        |
         lower bound of the CI --'          |        |
sample mean (center of the CI) -------------'        |
         upper bound of the CI ----------------------'

As described above, a change is considered significant if the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD).

For instance, for an execution time metric, this confidence interval indicates a significantly worse performance:

----------------------------------------|---------|---(---------^---------)---------->
                                       0%        1%  1.3%      2.2%      3.1%
                                                  |   |         |         |
       significant impact threshold --------------'   |         |         |
                      lower bound of CI --------------'         |         |
       sample mean (center of the CI) --------------------------'         |
                      upper bound of CI ----------------------------------'