feat: Add adaptive_sampling_target to config (#3406)

Author: amychisholm03

lib/config/default.js

@@ -1156,16 +1156,27 @@ defaultConfig.definition = () => {
       },
 
       sampler: {
-      /**
-       * When set to `always_on`, the sampled flag in the `traceparent` header
-       * being set to "true" will result in the local transaction being sampled
-       * with a priority value of "2". When set to `always_off`, the local
-       * transaction will never be sampled. At the default setting, the sampling
-       * decision will be determined according to the normal algorithm.
-       *
-       * This setting takes precedence over the `remote_parent_not_sampled`
-       * setting.
-       */
+        /**
+         * The sampling target for adaptive sampling is controlled via this attribute when configuring the default/adaptive sampler.
+         * The default sampling target is 10 transactions/min when it is not specified but **MUST** be within the range of [1, 120] (inclusive).
+         * Upon agent connect, the connect response **MUST** provide the value of `sampling_target` based on this configuration setting's value.
+         * The `sampling_target` value from the connect response **SHOULD** be used as the sampling target value for adaptive sampling in the agent.
+         */
+        adaptive_sampling_target: {
+          formatter: int,
+          default: 10
+        },
+
+        /**
+         * When set to `always_on`, the sampled flag in the `traceparent` header
+         * being set to "true" will result in the local transaction being sampled
+         * with a priority value of "2". When set to `always_off`, the local
+         * transaction will never be sampled. At the default setting, the sampling
+         * decision will be determined according to the normal algorithm.
+         *
+         * This setting takes precedence over the `remote_parent_not_sampled`
+         * setting.
+         */
         remote_parent_sampled: {
           formatter: allowList.bind(null, ['always_on', 'always_off', 'default']),
           default: 'default'

lib/config/index.js

@@ -123,7 +123,7 @@ function Config(config) {
   this.primary_application_id = null
   this.trusted_account_ids = null
   this.trusted_account_key = null
-  this.sampling_target = 10
+  this.sampling_target = this.distributed_tracing.sampler.adaptive_sampling_target
   this.sampling_target_period_in_seconds = 60
   this.max_payload_size_in_bytes = DEFAULT_MAX_PAYLOAD_SIZE_IN_BYTES
 

test/unit/config/config-defaults.test.js

@@ -329,6 +329,10 @@ test('with default properties', async (t) => {
     assert.equal(configuration.distributed_tracing.sampler.remote_parent_not_sampled, 'default')
   })
 
+  await t.test('adaptive sampling target should default to 10 transactions/min', () => {
+    assert.equal(configuration.distributed_tracing.sampler.adaptive_sampling_target, 10)
+  })
+
   await t.test('opentelemetry', () => {
     const otel = configuration.opentelemetry_bridge
     assert.equal(otel.enabled, false)