feat(otel): support DD_HOSTNAME as host.name OTel resource attribute

[mabdinur]

What does this PR do?

Adds a top-level hostname configuration option backed by the DD_HOSTNAME environment variable. When DD_TRACE_REPORT_HOSTNAME is enabled:

• DD_HOSTNAME is used as the host.name OpenTelemetry resource attribute (OTel metrics and logs), falling back to Socket.hostname if unset.
• DD_HOSTNAME is used as the trace-level hostname tag, matching the behavior of other Datadog SDKs.

Motivation:

The DD_HOSTNAME env var is supported by other Datadog SDKs (Python, Java, etc.) and allows overriding the host name reported by the process. This brings Ruby parity and allows the Test_FR07_Host_Name::test_hostname_from_dd_hostname parametric test to pass.

Alignment with dd-trace-py:

Reviewed the dd-trace-py implementation. Python uses a single get_hostname() helper that returns DD_HOSTNAME if set, else falls back to socket.gethostname(). This value is applied to:

• Traces: set on each span when report_hostname is true (_trace/tracer.py:564)
• OTel metrics resource: host.name attribute when report_hostname is true
• OTel logs resource: host.name attribute when report_hostname is true

This PR aligns Ruby with that pattern:

• Datadog.configuration.hostname (reads DD_HOSTNAME) takes precedence over the system hostname in traces and OTel resource attributes
• Missing RBS type declarations added: ENV_HOSTNAME constant and hostname method on Settings

Precedence (OTel resource host.name):

1. DD_HOSTNAME (explicit override)
2. host.name from DD_TAGS / c.tags
3. Socket.hostname (system fallback)

Change log entry

Yes. Added DD_HOSTNAME environment variable support. When DD_TRACE_REPORT_HOSTNAME is enabled, the value of DD_HOSTNAME is used as the trace hostname and host.name OpenTelemetry resource attribute.

Additional Notes:

• The same @settings.hostname fallback is applied in both the metrics (metrics.rb) and logs (lib/datadog/opentelemetry/logs.rb, in the companion PR feat(otel): add otel logs support #5446) resource builders.
• RBS types updated: ENV_HOSTNAME: String in sig/datadog/core/environment/ext.rbs and def hostname: -> String? in sig/datadog/core/configuration/settings.rbs.

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 4e099643c3

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[datadog-official]

✨ Fix all issues with BitsAI or with Cursor

⚠️ Warnings

❄️ 2 New flaky tests detected

Datadog::Core::Environment::Socket::resolved_hostname when DD_HOSTNAME is empty falls back to the system hostname from rspec     (Fix with Cursor)

expected: ""
     got: nil

(compared using ==)

Failure/Error: expect(resolved).to eq(described_class.hostname)

  expected: ""
       got: nil

...

Datadog::Core::Environment::Socket::resolved_hostname when DD_HOSTNAME is not set returns the system hostname from rspec     (Fix with Cursor)

expected: ""
     got: nil

(compared using ==)

Failure/Error: expect(resolved).to eq(described_class.hostname)

  expected: ""
       got: nil

...

ℹ️ Info

No other issues found (see more)

🧪 All tests passed

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 97.14% (-0.00%)

Useful? React with 👍 / 👎

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 99d570a | Docs | Datadog PR Page | Give us feedback!}

[pr-commenter]

Benchmarks

Benchmark execution time: 2026-05-11 15:38:55

Comparing candidate commit e8507ba in PR branch munir/otel-dd-hostname with baseline commit cbb6899 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 ----------------------------------'

[dd-octo-sts]

Typing analysis

This PR does not change typing compared to the base branch.

[mabdinur]

/merge

[gh-worker-devflow-routing-ef8351]

View all feedbacks in Devflow UI.

2026-05-11 17:54:08 UTC ℹ️ Start processing command /merge

---

2026-05-11 17:54:21 UTC ℹ️ MergeQueue: waiting for PR to be ready

This pull request is not mergeable according to GitHub. Common reasons include pending required checks, missing approvals, or merge conflicts — but it could also be blocked by other repository rules or settings.
It will be added to the queue as soon as checks pass and/or get approvals. View in MergeQueue UI.
Note: if you pushed new commits since the last approval, you may need additional approval.
You can remove it from the waiting list with /remove command.

---

2026-05-11 21:58:16 UTC ⚠️ MergeQueue: This merge request was unqueued

devflow unqueued this merge request: It did not become mergeable within the expected time