From 5de105695fa2b29fcfbab447a2a734f8281e3a3d Mon Sep 17 00:00:00 2001
From: Siim Kallas <siimkallas@gmail.com>
Date: Wed, 27 Nov 2024 13:42:55 +0200
Subject: [PATCH] feat: change the default sampler to be always on (#985)

* feat: change the default sampler to be always on

* run prebuilds on node 16
---
 .github/workflows/ci.yml           |  4 ++--
 src/tracing/options.ts             | 16 ++++++++++++++++
 src/types.ts                       |  1 +
 test/options.test.ts               |  3 +++
 test/tracing/default_setup.test.ts |  7 +++++++
 test/tracing/env_options.test.ts   |  8 ++++++++
 6 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 69cbe036..5560a120 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -14,7 +14,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        container: ['node:14.0.0']
+        container: ['node:16.0.0']
         node_api_target: ['18.0.0']
         include:
           - container: 'node:16.0.0'
@@ -42,7 +42,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        container: ['node:14.0.0']
+        container: ['node:16.0.0']
         node_api_target: ['18.0.0']
         include:
           - container: 'node:16.0.0'
diff --git a/src/tracing/options.ts b/src/tracing/options.ts
index cb6d11b6..7a10bf66 100644
--- a/src/tracing/options.ts
+++ b/src/tracing/options.ts
@@ -15,6 +15,7 @@
  */
 import * as util from 'util';
 import {
+  AlwaysOnSampler,
   ConsoleSpanExporter,
   SpanExporter,
   SpanProcessor,
@@ -49,6 +50,18 @@ import type {
   StartTracingOptions,
   TracingOptions,
 } from './types';
+import { NodeTracerConfig } from '@opentelemetry/sdk-trace-node';
+
+function defaultSampler(config: NodeTracerConfig) {
+  if (
+    config.sampler === undefined &&
+    getNonEmptyEnvVar('OTEL_TRACES_SAMPLER') === undefined
+  ) {
+    return new AlwaysOnSampler();
+  }
+
+  return undefined;
+}
 
 export function _setDefaultOptions(
   options: StartTracingOptions = {}
@@ -88,8 +101,11 @@ export function _setDefaultOptions(
   );
 
   const extraTracerConfig = options.tracerConfig || {};
+
+  const sampler = defaultSampler(extraTracerConfig);
   const tracerConfig = {
     resource,
+    sampler,
     ...extraTracerConfig,
   };
 
diff --git a/src/types.ts b/src/types.ts
index 2d02123b..cfa37cdd 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -41,6 +41,7 @@ export type EnvVarKey =
   | 'OTEL_SERVICE_NAME'
   | 'OTEL_SPAN_LINK_COUNT_LIMIT'
   | 'OTEL_TRACES_EXPORTER'
+  | 'OTEL_TRACES_SAMPLER'
   | 'SPLUNK_ACCESS_TOKEN'
   | 'SPLUNK_AUTOINSTRUMENT_PACKAGE_NAMES'
   | 'SPLUNK_AUTOMATIC_LOG_COLLECTION'
diff --git a/test/options.test.ts b/test/options.test.ts
index 8ab7cafd..06fefd6d 100644
--- a/test/options.test.ts
+++ b/test/options.test.ts
@@ -37,6 +37,7 @@ import {
   SimpleSpanProcessor,
   SpanExporter,
   InMemorySpanExporter,
+  AlwaysOffSampler,
 } from '@opentelemetry/sdk-trace-base';
 
 import { strict as assert } from 'assert';
@@ -212,6 +213,7 @@ describe('options', () => {
       instrumentations: [testInstrumentation],
       tracerConfig: {
         resource: new Resource({ attr1: 'value1' }),
+        sampler: new AlwaysOffSampler(),
         idGenerator: idGenerator,
       },
       resourceFactory,
@@ -230,6 +232,7 @@ describe('options', () => {
       instrumentations: [testInstrumentation],
       tracerConfig: {
         resource: new Resource({ attr1: 'value1' }),
+        sampler: new AlwaysOffSampler(),
         idGenerator: idGenerator,
       },
       spanExporterFactory: testSpanExporterFactory,
diff --git a/test/tracing/default_setup.test.ts b/test/tracing/default_setup.test.ts
index 33bc6882..c467d844 100644
--- a/test/tracing/default_setup.test.ts
+++ b/test/tracing/default_setup.test.ts
@@ -14,11 +14,14 @@
  * limitations under the License.
  */
 
+import { strict as assert } from 'assert';
 import { test } from 'node:test';
 import { assertTracingPipeline, setupMocks } from './common';
 
 import { parseOptionsAndConfigureInstrumentations } from '../../src/instrumentations';
 import { startTracing, stopTracing } from '../../src/tracing';
+import { trace } from '@opentelemetry/api';
+import { AlwaysOnSampler } from '@opentelemetry/sdk-trace-base';
 
 test('Tracing: set up with defaults', async () => {
   const mocks = setupMocks();
@@ -29,5 +32,9 @@ test('Tracing: set up with defaults', async () => {
     'http://localhost:4318/v1/traces',
     '@splunk/otel'
   );
+
+  const provider = trace.getTracerProvider();
+  assert(provider.getTracer('test')['_sampler'] instanceof AlwaysOnSampler);
+
   await stopTracing();
 });
diff --git a/test/tracing/env_options.test.ts b/test/tracing/env_options.test.ts
index c42cdfea..a0b07de8 100644
--- a/test/tracing/env_options.test.ts
+++ b/test/tracing/env_options.test.ts
@@ -14,11 +14,14 @@
  * limitations under the License.
  */
 
+import { strict as assert } from 'assert';
 import { test } from 'node:test';
 import { assertTracingPipeline, setupMocks } from './common';
 
 import { parseOptionsAndConfigureInstrumentations } from '../../src/instrumentations';
 import { startTracing, stopTracing } from '../../src/tracing';
+import { trace } from '@opentelemetry/api';
+import { ParentBasedSampler } from '@opentelemetry/sdk-trace-base';
 
 test('Tracing: set up with env options', async () => {
   const mocks = setupMocks();
@@ -30,9 +33,14 @@ test('Tracing: set up with env options', async () => {
   process.env.OTEL_EXPORTER_OTLP_ENDPOINT = url;
   process.env.OTEL_SERVICE_NAME = serviceName;
   process.env.SPLUNK_ACCESS_TOKEN = accessToken;
+  process.env.OTEL_TRACES_SAMPLER = 'parentbased_always_on';
 
   const { tracingOptions } = parseOptionsAndConfigureInstrumentations();
   startTracing(tracingOptions);
   assertTracingPipeline(mocks, `${url}/v1/traces`, serviceName, accessToken);
+
+  const provider = trace.getTracerProvider();
+  assert(provider.getTracer('test')['_sampler'] instanceof ParentBasedSampler);
+
   await stopTracing();
 });