feat(opentelemetry-sampler-aws-xray): Add Rate Limiter and Sampling Targets Poller Logic

incubator/opentelemetry-sampler-aws-xray/src/aws-xray-sampling-client.ts

@@ -45,7 +45,7 @@ export class AWSXRaySamplingClient {
     this.makeSamplingRequest<GetSamplingTargetsResponse>(
       this.samplingTargetsEndpoint,
       callback,
-      this.samplerDiag.debug,
+      (message: string) => this.samplerDiag.debug(message),
       JSON.stringify(requestBody)
     );
   }
@@ -56,7 +56,7 @@ export class AWSXRaySamplingClient {
     this.makeSamplingRequest<GetSamplingRulesResponse>(
       this.getSamplingRulesEndpoint,
       callback,
-      this.samplerDiag.error
+      (message: string) => this.samplerDiag.error(message)
     );
   }
 

incubator/opentelemetry-sampler-aws-xray/src/fallback-sampler.ts

@@ -21,16 +21,20 @@
 import { Attributes, Context, Link, SpanKind } from '@opentelemetry/api';
 import {
   Sampler,
+  SamplingDecision,
   SamplingResult,
   TraceIdRatioBasedSampler,
 } from '@opentelemetry/sdk-trace-base';
+import { RateLimitingSampler } from './rate-limiting-sampler';
 
 // FallbackSampler samples 1 req/sec and additional 5% of requests using TraceIdRatioBasedSampler.
 export class FallbackSampler implements Sampler {
   private fixedRateSampler: TraceIdRatioBasedSampler;
+  private rateLimitingSampler: RateLimitingSampler;
 
-  constructor() {
-    this.fixedRateSampler = new TraceIdRatioBasedSampler(0.05);
+  constructor(ratio = 0.05, quota = 1) {
+    this.fixedRateSampler = new TraceIdRatioBasedSampler(ratio);
+    this.rateLimitingSampler = new RateLimitingSampler(quota);
   }
 
   shouldSample(
@@ -41,7 +45,19 @@ export class FallbackSampler implements Sampler {
     attributes: Attributes,
     links: Link[]
   ): SamplingResult {
-    // TODO: implement and use Rate Limiting Sampler
+    const samplingResult: SamplingResult =
+      this.rateLimitingSampler.shouldSample(
+        context,
+        traceId,
+        spanName,
+        spanKind,
+        attributes,
+        links
+      );
+
+    if (samplingResult.decision !== SamplingDecision.NOT_RECORD) {
+      return samplingResult;
+    }
 
     return this.fixedRateSampler.shouldSample(context, traceId);
   }

incubator/opentelemetry-sampler-aws-xray/src/rate-limiter.ts

@@ -0,0 +1,65 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// Includes work from:
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+/*
+ * The RateLimiter keeps track of the current reservoir quota balance available (measured via available time)
+ * If enough time has elapsed, the RateLimiter will allow quota balance to be consumed/taken (decrease available time)
+ * A RateLimitingSampler uses this RateLimiter to determine if it should sample or not based on the quota balance available.
+ */
+export class RateLimiter {
+  // Quota assigned to client to dictate maximum quota balance that can be consumed per second.
+  private quota: number;
+  private MAX_BALANCE_MILLIS: number;
+  // Used to measure current quota balance.
+  private walletFloorMillis: number;
+
+  constructor(quota: number, maxBalanceInSeconds = 1) {
+    this.MAX_BALANCE_MILLIS = maxBalanceInSeconds * 1000.0;
+    this.quota = quota;
+    this.walletFloorMillis = Date.now();
+    // current "balance" would be `ceiling - floor`
+  }
+
+  public take(cost = 1): boolean {
+    if (this.quota === 0) {
+      return false;
+    }
+
+    // assume divide by zero not possible
+    const costInMillis: number = (cost * 1000.0) / this.quota;
+
+    const walletCeilingMillis: number = Date.now();
+    let currentBalanceMillis: number =
+      walletCeilingMillis - this.walletFloorMillis;
+    currentBalanceMillis = Math.min(
+      currentBalanceMillis,
+      this.MAX_BALANCE_MILLIS
+    );
+    const pendingRemainingBalanceMillis: number =
+      currentBalanceMillis - costInMillis;
+    if (pendingRemainingBalanceMillis >= 0) {
+      this.walletFloorMillis =
+        walletCeilingMillis - pendingRemainingBalanceMillis;
+      return true;
+    }
+    // No changes to the wallet state
+    return false;
+  }
+}

incubator/opentelemetry-sampler-aws-xray/src/rate-limiting-sampler.ts

@@ -0,0 +1,58 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// Includes work from:
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+import { Attributes, Context, Link, SpanKind } from '@opentelemetry/api';
+import {
+  Sampler,
+  SamplingDecision,
+  SamplingResult,
+} from '@opentelemetry/sdk-trace-base';
+import { RateLimiter } from './rate-limiter';
+
+export class RateLimitingSampler implements Sampler {
+  private quota: number;
+  private reservoir: RateLimiter;
+
+  constructor(quota: number) {
+    this.quota = quota;
+    this.reservoir = new RateLimiter(quota);
+  }
+
+  shouldSample(
+    context: Context,
+    traceId: string,
+    spanName: string,
+    spanKind: SpanKind,
+    attributes: Attributes,
+    links: Link[]
+  ): SamplingResult {
+    if (this.reservoir.take(1)) {
+      return {
+        decision: SamplingDecision.RECORD_AND_SAMPLED,
+        attributes: attributes,
+      };
+    }
+    return { decision: SamplingDecision.NOT_RECORD, attributes: attributes };
+  }
+
+  public toString(): string {
+    return `RateLimitingSampler{rate limiting sampling with sampling config of ${this.quota} req/sec and 0% of additional requests}`;
+  }
+}

incubator/opentelemetry-sampler-aws-xray/src/remote-sampler.ts

@@ -36,11 +36,19 @@ import { FallbackSampler } from './fallback-sampler';
 import {
   AWSXRayRemoteSamplerConfig,
   GetSamplingRulesResponse,
+  GetSamplingTargetsBody,
+  GetSamplingTargetsResponse,
   SamplingRuleRecord,
+  SamplingTargetDocument,
+  TargetMap,
 } from './types';
-import { RuleCache } from './rule-cache';
+import {
+  DEFAULT_TARGET_POLLING_INTERVAL_SECONDS,
+  RuleCache,
+} from './rule-cache';
 
 import { SamplingRuleApplier } from './sampling-rule-applier';
+import { PACKAGE_NAME } from './version';
 
 // 5 minute default sampling rules polling interval
 const DEFAULT_RULES_POLLING_INTERVAL_SECONDS: number = 5 * 60;
@@ -94,17 +102,22 @@ export class AWSXRayRemoteSampler implements Sampler {
 // Not intended for external use, use Parent-based `AWSXRayRemoteSampler` instead.
 export class _AWSXRayRemoteSampler implements Sampler {
   private rulePollingIntervalMillis: number;
+  private targetPollingInterval: number;
   private awsProxyEndpoint: string;
   private ruleCache: RuleCache;
   private fallbackSampler: FallbackSampler;
   private samplerDiag: DiagLogger;
   private rulePoller: NodeJS.Timeout | undefined;
+  private targetPoller: NodeJS.Timeout | undefined;
   private clientId: string;
   private rulePollingJitterMillis: number;
+  private targetPollingJitterMillis: number;
   private samplingClient: AWSXRaySamplingClient;
 
   constructor(samplerConfig: AWSXRayRemoteSamplerConfig) {
-    this.samplerDiag = diag;
+    this.samplerDiag = diag.createComponentLogger({
+      namespace: PACKAGE_NAME,
+    });
 
     if (
       samplerConfig.pollingInterval == null ||
@@ -120,6 +133,8 @@ export class _AWSXRayRemoteSampler implements Sampler {
     }
 
     this.rulePollingJitterMillis = Math.random() * 5 * 1000;
+    this.targetPollingInterval = this.getDefaultTargetPollingInterval();
+    this.targetPollingJitterMillis = (Math.random() / 10) * 1000;
 
     this.awsProxyEndpoint = samplerConfig.endpoint
       ? samplerConfig.endpoint
@@ -137,7 +152,12 @@ export class _AWSXRayRemoteSampler implements Sampler {
     // Start the Sampling Rules poller
     this.startSamplingRulesPoller();
 
-    // TODO: Start the Sampling Targets poller
+    // Start the Sampling Targets poller where the first poll occurs after the default interval
+    this.startSamplingTargetsPoller();
+  }
+
+  public getDefaultTargetPollingInterval(): number {
+    return DEFAULT_TARGET_POLLING_INTERVAL_SECONDS;
   }
 
   public shouldSample(
@@ -203,6 +223,7 @@ export class _AWSXRayRemoteSampler implements Sampler {
 
   public stopPollers() {
     clearInterval(this.rulePoller);
+    clearInterval(this.targetPoller);
   }
 
   private startSamplingRulesPoller(): void {
@@ -216,6 +237,27 @@ export class _AWSXRayRemoteSampler implements Sampler {
     this.rulePoller.unref();
   }
 
+  private startSamplingTargetsPoller(): void {
+    // Update sampling targets every targetPollingInterval (usually 10 seconds)
+    this.targetPoller = setInterval(
+      () => this.getAndUpdateSamplingTargets(),
+      this.targetPollingInterval * 1000 + this.targetPollingJitterMillis
+    );
+    this.targetPoller.unref();
+  }
+
+  private getAndUpdateSamplingTargets(): void {
+    const requestBody: GetSamplingTargetsBody = {
+      SamplingStatisticsDocuments:
+        this.ruleCache.createSamplingStatisticsDocuments(this.clientId),
+    };
+
+    this.samplingClient.fetchSamplingTargets(
+      requestBody,
+      this.updateSamplingTargets.bind(this)
+    );
+  }
+
   private getAndUpdateSamplingRules(): void {
     this.samplingClient.fetchSamplingRules(this.updateSamplingRules.bind(this));
   }
@@ -242,6 +284,41 @@ export class _AWSXRayRemoteSampler implements Sampler {
     }
   }
 
+  private updateSamplingTargets(
+    responseObject: GetSamplingTargetsResponse
+  ): void {
+    try {
+      const targetDocuments: TargetMap = {};
+
+      // Create Target-Name-to-Target-Map from sampling targets response
+      responseObject.SamplingTargetDocuments.forEach(
+        (newTarget: SamplingTargetDocument) => {
+          targetDocuments[newTarget.RuleName] = newTarget;
+        }
+      );
+
+      // Update targets in the cache
+      const [refreshSamplingRules, nextPollingInterval]: [boolean, number] =
+        this.ruleCache.updateTargets(
+          targetDocuments,
+          responseObject.LastRuleModification
+        );
+      this.targetPollingInterval = nextPollingInterval;
+      clearInterval(this.targetPoller);
+      this.startSamplingTargetsPoller();
+
+      if (refreshSamplingRules) {
+        this.samplerDiag.debug(
+          'Performing out-of-band sampling rule polling to fetch updated rules.'
+        );
+        clearInterval(this.rulePoller);
+        this.startSamplingRulesPoller();
+      }
+    } catch (error: unknown) {
+      this.samplerDiag.debug('Error occurred when updating Sampling Targets');
+    }
+  }
+
   private static generateClientId(): string {
     const hexChars: string[] = [
       '0',