Sandbox::https://github.com/nodejs/node/pull/66587

bengl · 2026-10-08T05:08:31Z

Adds experimental OpenTelemetry tracing support, as described in the included docs. Tracing is activated via environment variables only and requires the --experimental-otel flag.

There is no programmatic API yet. Custom instrumentation is not supported.

Assisted-by: pi:glm-5.3

This is a re-hash of #61907 restricting it to the OOTB behaviour only, leaving any API surface as an exercise for future PRs (and decisions around them). All configuration is currently through env vars. Most if not all still-relevant review comments from the previous PR are addressed here. In addition, a benchmark is added to measure future improvements.

Metrics and logging signals are also left to future PRs.

Adds experimental OpenTelemetry tracing support, as described in the included docs. Tracing is activated via environment variables only and requires the --experimental-otel flag. There is no programmatic API yet. Custom instrumentation is not supported. Assisted-by: pi:glm-5.3 Signed-off-by: Bryan English <bryan@bryanenglish.com>

nodejs-github-bot · 2026-10-08T05:08:37Z

Review requested:

@nodejs/config
@nodejs/performance

atlowChemi · 2026-10-08T05:48:20Z

+### `NODE_OTEL_ENDPOINT=url`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - Experimental
+
+When set to a non-empty value while the [`--experimental-otel`][] flag is
+enabled, activates the built-in OpenTelemetry tracing subsystem and directs
+spans to the specified OTLP/HTTP collector endpoint. The endpoint must be
+the base URL of the collector: any path present in the endpoint is
+replaced with `/v1/traces`, and an endpoint that already ends with
+`/v1/traces` is used as is. If `NODE_OTEL` is also set, `NODE_OTEL_ENDPOINT`
+takes precedence for the endpoint. See the [OpenTelemetry][] documentation
+for details.


Probably should also mention the default is http://localhost:4318?

atlowChemi · 2026-10-08T06:12:46Z

+                                 filter);
+}
+
+function start(options = { __proto__: null }) {


Require and use kEmptyObject from internal/util?

Suggested change

function start(options = { __proto__: null }) {

function start(options = kEmptyObject) {

atlowChemi · 2026-10-08T06:27:00Z

+### `NODE_OTEL_ENDPOINT`
+
+When set to a non-empty value, activates the tracing subsystem and directs
+spans to the specified OTLP collector endpoint. The endpoint should be the
+base URL of an OTLP/HTTP collector (e.g. `http://localhost:4318`) without
+a path: any path present in the endpoint is replaced with `/v1/traces`,
+and an endpoint that already ends with `/v1/traces` is used as is.
+
+```bash
+NODE_OTEL_ENDPOINT=http://collector.example.com:4318 \
+  node --experimental-otel app.js
+```


Here too, I think it should explicitly mention the default, even though the NODE_OTEL section mentions its default

Maybe

Suggested change

### `NODE_OTEL_ENDPOINT`

When set to a non-empty value, activates the tracing subsystem and directs

spans to the specified OTLP collector endpoint. The endpoint should be the

base URL of an OTLP/HTTP collector (e.g. `http://localhost:4318`) without

a path: any path present in the endpoint is replaced with `/v1/traces`,

and an endpoint that already ends with `/v1/traces` is used as is.

```bash

NODE_OTEL_ENDPOINT=http://collector.example.com:4318 \

node --experimental-otel app.js

```

### `NODE_OTEL_ENDPOINT`

When set to a non-empty value, activates the tracing subsystem and directs

spans to the specified OTLP collector endpoint. The endpoint should be the

base URL of an OTLP/HTTP collector (defaults to `http://localhost:4318`) without

a path: any path present in the endpoint is replaced with `/v1/traces`,

and an endpoint that already ends with `/v1/traces` is used as is.

```bash

NODE_OTEL_ENDPOINT=http://collector.example.com:4318 \

node --experimental-otel app.js

```

codecov · 2026-10-08T06:52:04Z

Codecov Report

❌ Patch coverage is 91.90751% with 84 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.44%. Comparing base (7514ef8) to head (a6861a5).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/otel/flush.js	88.88%	39 Missing and 1 partial ⚠️
lib/internal/otel/instrumentations.js	90.60%	21 Missing and 4 partials ⚠️
lib/internal/otel/span.js	94.31%	8 Missing and 2 partials ⚠️
lib/internal/otel/core.js	93.33%	8 Missing ⚠️
lib/internal/process/pre_execution.js	98.24%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #66587      +/-   ##
==========================================
- Coverage   92.79%   90.44%   -2.35%     
==========================================
  Files         422      796     +374     
  Lines      193669   277600   +83931     
  Branches    29886    53321   +23435     
==========================================
+ Hits       179712   251082   +71370     
- Misses      13630    16921    +3291     
- Partials      327     9597    +9270

Files with missing lines	Coverage Δ
lib/internal/otel/id.js	`100.00% <100.00%> (ø)`
src/node_options.cc	`81.73% <100.00%> (ø)`
src/node_options.h	`95.67% <100.00%> (ø)`
lib/internal/process/pre_execution.js	`96.61% <98.24%> (+19.02%)`	⬆️
lib/internal/otel/core.js	`93.33% <93.33%> (ø)`
lib/internal/otel/span.js	`94.31% <94.31%> (ø)`
lib/internal/otel/instrumentations.js	`90.60% <90.60%> (ø)`
lib/internal/otel/flush.js	`88.88% <88.88%> (ø)`

... and 496 files with indirect coverage changes

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

jasnell

First pass... Generally looks reasonable. Main concern is on instrumentation cost. Left a couple comments.

jasnell · 2026-10-08T07:02:29Z

+  }
+
+  setAttribute(key, value) {
+    this.#attributes[key] = value;


#attributes is going to be put into a slow dictionary mode with a internal shape transition every time an attribute is set... Meaning this is going to have a non-trivial cost.

Could this use a SafeMap instead?

Obviously that makes getAttributes trickier below but I would assume that setAttribute is the hotter path?

jasnell · 2026-10-08T07:05:30Z

+  }
+
+  addEvent(name, attributes) {
+    ArrayPrototypePush(this.#events, {


How many events might we expect? If it's a lot, or completely unbounded, this becomes quadratic after a while.

jsumners-nr · 2026-10-08T11:40:26Z

+The subsystem is independent of the OpenTelemetry JavaScript packages. It
+is not interoperable with `@opentelemetry/api`, and spans created by one
+are not visible to the other. Running both in the same process produces
+duplicate trace and span IDs. The built-in instrumentation also
+overwrites the `traceparent` (and, when present, `tracestate`) header on
+outgoing HTTP requests, discarding whatever a userland propagator may
+have set. Users should run either the built-in subsystem or a userland
+OpenTelemetry SDK, not both.


Then I wonder what the purpose of this is. From my perspective, this feature should work in one of two ways:

Provides an implementation of the API such that compliant instrumentations can register with it and it delivers the appropriate signals data to a collector.

Registers with whatever OTEL implementation is present such that the signals data is inlined correctly.

With the caveats highlighted in this paragraph, I'm just not clear what this accomplishes.

nodejs-github-bot added lib / src Issues and PRs involving general changes in the lib/ or src/ directories. needs-ci PRs that need a full CI run. labels Oct 8, 2026

bengl requested review from Flarna and Qard October 8, 2026 05:09

bengl mentioned this pull request Oct 8, 2026

otel: add new module #61907

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atlowChemi reviewed Oct 8, 2026

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lib: add built-in OpenTelemetry tracing - #66587

lib: add built-in OpenTelemetry tracing#66587
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	function start(options = { __proto__: null }) {
	function start(options = kEmptyObject) {

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