feat(sdk-node): wire up tracer_provider.sampler from declarative config

experimental/CHANGELOG.md

@@ -18,6 +18,7 @@ For notes on migrating to 2.x / 0.200.x see [the upgrade guide](doc/upgrade-to-2
 
 * feat(configuration): bump config schema to v1.1.0; rename `without_scope_info` → `scope_info_enabled` and `without_target_info/development` → `target_info_enabled/development` on the Prometheus pull exporter (semantics inverted), rename `with_resource_constant_labels` → `resource_constant_labels`. Validate `file_format` per the configuration versioning spec: accept any minor version of major `1` (e.g. `1.0`, `1.1`), warn when the minor version is newer than supported, and reject other major versions. [#6781](https://github.com/open-telemetry/opentelemetry-js/pull/6781) @MikeGoldsmith
 * feat(sdk-node): wire up `id_generator` from declarative config [#6782](https://github.com/open-telemetry/opentelemetry-js/pull/6782) @MikeGoldsmith
+* feat(sdk-node): wire up `tracer_provider.sampler` from declarative config (always_on, always_off, trace_id_ratio_based, parent_based); unrecognized variants warn and fall back to ParentBased(AlwaysOn) [#6506](https://github.com/open-telemetry/opentelemetry-js/issues/6506) @MikeGoldsmith
 * feat(propagator-env-carrier): empty name normalization [#6827](https://github.com/open-telemetry/opentelemetry-js/pull/6827) @pellared
 
 ### :bug: Bug Fixes

experimental/packages/opentelemetry-sdk-node/src/start.ts

@@ -17,6 +17,7 @@ import {
 } from '@opentelemetry/api';
 import {
   getIdGeneratorFromConfiguration,
+  getSamplerFromConfiguration,
   getInstanceID,
   createLoggerProviderFromConfig,
   getMeterReadersFromConfiguration,
@@ -168,11 +169,12 @@ function create(
     const spanProcessors = getSpanProcessorsFromConfiguration(config);
     if (spanProcessors) {
       const idGenerator = getIdGeneratorFromConfiguration(config);
-      // TODO (6506): support sampler configuration from config
+      const sampler = getSamplerFromConfiguration(config);
       const tracerProvider = new TracerProvider({
         resource,
         spanProcessors,
         idGenerator,
+        sampler,
         spanLimits: createSpanLimitsFromConfig(
           config.tracer_provider?.limits,
           config.attribute_limits

experimental/packages/opentelemetry-sdk-node/src/utils.ts

@@ -1273,6 +1273,21 @@ export function getInstanceID(config: ConfigurationModel): string | undefined {
 
 const DEFAULT_RATIO = 1;
 
+/**
+ * Returns the {@link Sampler} configured under `tracer_provider.sampler` in
+ * the declarative configuration, or `undefined` if none is set (in which case
+ * the SDK applies its default sampler).
+ */
+export function getSamplerFromConfiguration(
+  config: ConfigurationModel
+): Sampler | undefined {
+  const samplerConfig = config.tracer_provider?.sampler;
+  if (!samplerConfig) {
+    return undefined;
+  }
+  return buildSamplerFromConfig(samplerConfig);
+}
+
 /**
  * Builds a {@link Sampler} from a {@link SamplerConfigModel} data model.
  * This allows sampler construction from declarative configuration.
@@ -1309,7 +1324,7 @@ export function buildSamplerFromConfig(
         : undefined,
     });
   }
-  diag.error('Unknown sampler config, defaulting to ParentBased(AlwaysOn).');
+  diag.warn('Unknown sampler config, defaulting to ParentBased(AlwaysOn).');
   return new ParentBasedSampler({ root: new AlwaysOnSampler() });
 }
 

experimental/packages/opentelemetry-sdk-node/test/buildSamplerFromConfig.test.ts

@@ -4,13 +4,17 @@
  */
 
 import * as assert from 'assert';
+import type { ConfigurationModel } from '@opentelemetry/configuration';
 import {
   AlwaysOffSampler,
   AlwaysOnSampler,
   ParentBasedSampler,
   TraceIdRatioBasedSampler,
 } from '@opentelemetry/sdk-trace';
-import { buildSamplerFromConfig } from '../src/utils';
+import {
+  buildSamplerFromConfig,
+  getSamplerFromConfiguration,
+} from '../src/utils';
 
 describe('buildSamplerFromConfig()', () => {
   it('should return AlwaysOnSampler for always_on config', () => {
@@ -107,3 +111,43 @@ describe('buildSamplerFromConfig()', () => {
     );
   });
 });
+
+describe('getSamplerFromConfiguration()', () => {
+  it('returns undefined when tracer_provider.sampler is omitted', () => {
+    assert.strictEqual(
+      getSamplerFromConfiguration({} as ConfigurationModel),
+      undefined
+    );
+    assert.strictEqual(
+      getSamplerFromConfiguration({
+        tracer_provider: { processors: [] },
+      } as ConfigurationModel),
+      undefined
+    );
+  });
+
+  it('returns the sampler defined under tracer_provider.sampler', () => {
+    const sampler = getSamplerFromConfiguration({
+      tracer_provider: {
+        processors: [],
+        sampler: { always_off: {} },
+      },
+    } as ConfigurationModel);
+    assert.ok(sampler instanceof AlwaysOffSampler);
+  });
+
+  it('builds a parent_based sampler from configuration', () => {
+    const sampler = getSamplerFromConfiguration({
+      tracer_provider: {
+        processors: [],
+        sampler: {
+          parent_based: { root: { trace_id_ratio_based: { ratio: 0.25 } } },
+        },
+      },
+    } as ConfigurationModel);
+    assert.ok(sampler instanceof ParentBasedSampler);
+    assert.ok(
+      sampler.toString().startsWith('ParentBased{root=TraceIdRatioBased{0.25}')
+    );
+  });
+});