feat(config): support OTEL_PROPAGATORS as propagation style fallback by bm1549 · Pull Request #271 · DataDog/dd-trace-rs

bm1549 · 2026-06-30T21:07:54Z

What does this PR do?

Adds support for the OpenTelemetry OTEL_PROPAGATORS env var as a fallback for DD_TRACE_PROPAGATION_STYLE. When DD_TRACE_PROPAGATION_STYLE is unset, dd-trace-rs reads OTEL_PROPAGATORS and applies it to the global propagation style, matching the other Datadog tracers (Python, Go, Java, Node.js, .NET, Ruby, PHP).

It reuses the existing update_non_empty_string_with_fallback helper (the one behind the OTEL_SERVICE_NAME alias), so only the global style is wired; extract/inject inherit it through the existing fallback in propagation/config.rs. Supported values: datadog, tracecontext, baggage, b3 (single-header), b3multi, none. Unsupported OpenTelemetry propagators (jaeger, xray, ottrace) are dropped with a warning. DD_TRACE_PROPAGATION_STYLE wins when both are set.

Motivation

Users who configure propagation via OTEL_PROPAGATORS expect dd-trace-rs to honor it the way the other tracers do. It was the only tracer (besides dd-trace-cpp) missing it.

Additional Notes

An empty DD_TRACE_PROPAGATION_STYLE="" is now treated as unset (falls back to OTEL_PROPAGATORS, then the default), consistent with the OTEL_SERVICE_NAME fallback.
Companion system-tests PR: fix(rust/parametric): report effective propagation style in /trace/config system-tests#7241.

🤖 Generated with Claude Code

…OPAGATION_STYLE

Adds 6 new unit tests covering: - DD wins precedence over OTEL_PROPAGATORS - Unsupported propagator names are filtered out - Baggage and None styles are supported - Extract/inject inherit global style from OTEL_PROPAGATORS - Mixed DD_TRACE_PROPAGATION_STYLE_EXTRACT + OTEL_PROPAGATORS precedence - Default style when no env vars set Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

CONTRIBUTING.md requires test-only imports at the top of the `mod tests` block rather than inside individual test functions. Moves the get_extractors/get_injectors import out of the two test bodies. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

datadog-prod-us1-4 · 2026-06-30T21:08:20Z

Tests

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

_{This comment will be updated automatically if new data arrives.

🔗 Commit SHA: 9667a09 | Docs | Datadog PR Page | Give us feedback!}

The Feature Parity Dashboard registers OTEL_PROPAGATORS (version A) with an empty-string default, not null. The config-inversion local validation job (validate_supported_configurations_v2_local_file) rejected the null default as a registry mismatch. Align the entry with the registry. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Drops the bespoke update_parsed_with_transform_with_fallback helper and wires OTEL_PROPAGATORS onto trace_propagation_style via the existing update_non_empty_string_with_fallback (the same helper used for the OTEL_SERVICE_NAME alias), splitting the comma-separated value in the transform closure. This makes the two OTEL_* aliases consistent: an empty DD_TRACE_PROPAGATION_STYLE is now treated as unset (falls back to OTEL_PROPAGATORS, then the default) rather than yielding an empty style list. Updates the two propagation tests that asserted the old empty-string-as-empty-list behavior. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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chatgpt-codex-connector · 2026-07-02T18:59:11Z

+            trace_propagation_style: cisu.update_non_empty_string_with_fallback(
+                default.trace_propagation_style,
+                SupportedConfigurations::OTEL_PROPAGATORS,


Honor DD-specific propagation style precedence

With DD_TRACE_PROPAGATION_STYLE_EXTRACT=datadog and OTEL_PROPAGATORS=tracecontext, this fallback still sets the global style from OTEL, so get_injectors (which falls back to the global style when _INJECT is absent) injects only tracecontext instead of the default global styles. Datadog documents OTEL_PROPAGATORS as lowest precedence and ignored when another Datadog trace context propagation variable is set (https://docs.datadoghq.com/tracing/trace_collection/trace_context_propagation/), so the fallback should also be skipped when the extract/inject style keys are present.

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Checked the other tracers on this. For this exact case (DD_TRACE_PROPAGATION_STYLE_EXTRACT set, global + _INJECT unset, OTEL_PROPAGATORS set), inject also inherits OTEL_PROPAGATORS in dd-trace-py, dd-trace-go, dd-trace-java, and dd-trace-js — only php/rb fall back to the default. Here OTEL_PROPAGATORS is a fallback for the global DD_TRACE_PROPAGATION_STYLE, and extract/inject inherit the global when their own key isn't set (existing get_extractors/get_injectors behavior), so this matches the reference impls. Agreed the php/rb split isn't ideal and probably deserves a cross-tracer alignment, but that's out of scope for this PR — keeping as-is here.

iunanua

Is possible to enable the corresponding system tests? Although I've taken a quick look, it seems to me that to enable them, we need to support other otel env vars.

iunanua · 2026-07-03T08:29:20Z

+        // Unknown propagator names (e.g. "jaeger") are dropped; supported ones are kept.
+        let mut sources = CompositeSource::new();
+        sources.add_source(HashMapSource::from_iter(
+            [("OTEL_PROPAGATORS", "jaeger,tracecontext")],


when DD_TRACE_PROPAGATION_STYLE is unset and OTEL_PROPAGATORS=unsupported_style, I think config.trace_propagation_style() returns an empty array. Should it return the default values instead?

yep good point, done in 9667a09 - all-unsupported OTEL_PROPAGATORS now falls back to the default instead of an empty list.

…all-unsupported Addresses review feedback: - Reuse the DdTags wrapper in the fallback transform instead of an inline comma-split, matching the extract/inject closures. - When the global propagation style parses to no recognized styles (e.g. OTEL_PROPAGATORS=jaeger with only unsupported values), fall back to the default set rather than silently disabling propagation. Reads the default from the existing ConfigItem so the list isn't duplicated. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

bm1549 · 2026-07-06T15:28:30Z

@iunanua Dug into this - it's mostly harness gaps, not missing OTEL vars. The test_otel_env_vars.py cases assert on dd_trace_sample_rate (the rust parametric /trace/config returns null), and the test_telemetry.py cases need the otel.env.hiding/otel.env.invalid metrics that aren't wired up here - so enabling them is a follow-up, out of scope for this PR.

…271) # What does this PR do? Adds support for the OpenTelemetry `OTEL_PROPAGATORS` env var as a fallback for `DD_TRACE_PROPAGATION_STYLE`. When `DD_TRACE_PROPAGATION_STYLE` is unset, dd-trace-rs reads `OTEL_PROPAGATORS` and applies it to the global propagation style, matching the other Datadog tracers (Python, Go, Java, Node.js, .NET, Ruby, PHP). It reuses the existing `update_non_empty_string_with_fallback` helper (the one behind the `OTEL_SERVICE_NAME` alias), so only the global style is wired; extract/inject inherit it through the existing fallback in `propagation/config.rs`. Supported values: `datadog`, `tracecontext`, `baggage`, `b3` (single-header), `b3multi`, `none`. Unsupported OpenTelemetry propagators (`jaeger`, `xray`, `ottrace`) are dropped with a warning. `DD_TRACE_PROPAGATION_STYLE` wins when both are set. # Motivation Users who configure propagation via `OTEL_PROPAGATORS` expect dd-trace-rs to honor it the way the other tracers do. It was the only tracer (besides dd-trace-cpp) missing it. # Additional Notes - An empty `DD_TRACE_PROPAGATION_STYLE=""` is now treated as unset (falls back to `OTEL_PROPAGATORS`, then the default), consistent with the `OTEL_SERVICE_NAME` fallback. - Companion system-tests PR: DataDog/system-tests#7241. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-authored-by: brian.marks <brian.marks@datadoghq.com>

bm1549 and others added 5 commits June 30, 2026 16:32

feat(config): register OTEL_PROPAGATORS configuration key

b6456dd

feat(propagation): honor OTEL_PROPAGATORS as fallback for DD_TRACE_PR…

ecf8531

…OPAGATION_STYLE

test(propagation): cover OTEL_PROPAGATORS multi-source precedence

41288b6

bm1549 added the ai generated label Jun 30, 2026

bm1549 mentioned this pull request Jun 30, 2026

fix(rust/parametric): report effective propagation style in /trace/config DataDog/system-tests#7241

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bm1549 and others added 2 commits June 30, 2026 17:11

bm1549 marked this pull request as ready for review July 2, 2026 18:52

bm1549 requested a review from a team as a code owner July 2, 2026 18:52

chatgpt-codex-connector Bot reviewed Jul 2, 2026

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iunanua approved these changes Jul 3, 2026

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gh-worker-dd-devflow-36fce6 Bot added mergequeue-status: queued mergequeue-status: in_progress and removed mergequeue-status: queued labels Jul 6, 2026

gh-worker-dd-mergequeue-cf854d Bot merged commit e2d2e95 into main Jul 6, 2026
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gh-worker-dd-mergequeue-cf854d Bot deleted the brian.marks/otel-propagators branch July 6, 2026 15:53

gh-worker-dd-devflow-36fce6 Bot added the mergequeue-status: done label Jul 6, 2026

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feat(config): support OTEL_PROPAGATORS as propagation style fallback#271

feat(config): support OTEL_PROPAGATORS as propagation style fallback#271
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