NestJS + Opentelemetry (Sampling)

import { TraceIdRatioBasedSampler } from '@opentelemetry/sdk-trace-node';

const samplePercentage = 0.1;

const sdk = new NodeSDK({
  // Other SDK configuration parameters go here
  sampler: new TraceIdRatioBasedSampler(samplePercentage),
});

import { Context } from "@opentelemetry/api";
import {
  SpanProcessor,
  ReadableSpan,
  Span,
} from "@opentelemetry/sdk-trace-node";

/**
 * Sampling span processor (including all error span and ratio of other spans)
 */
export class SamplingSpanProcessor implements SpanProcessor {
  constructor(
    private _spanProcessor: SpanProcessor,
    private _ratio: number
  ) {}

  /**
   * Forces to export all finished spans
   */
  forceFlush(): Promise<void> {
    return this._spanProcessor.forceFlush();
  }

  onStart(span: Span, parentContext: Context): void {
    this._spanProcessor.onStart(span, parentContext);
  }

  shouldSample(traceId: string): boolean {
    let accumulation = 0;
    for (let idx = 0; idx < traceId.length; idx++) {
      accumulation += traceId.charCodeAt(idx);
    }
    const cmp = (accumulation % 100) / 100;
    return cmp < this._ratio;
  }

  /**
   * Called when a {@link ReadableSpan} is ended, if the `span.isRecording()`
   * returns true.
   * @param span the Span that just ended.
   */
  onEnd(span: ReadableSpan): void {
    // Only process spans that have an error status
    if (span.status.code === 2) {
      // Status code 0 means "UNSET", 1 means "OK", and 2 means "ERROR"
      this._spanProcessor.onEnd(span);
    } else {
      if (this.shouldSample(span.spanContext().traceId)) {
        this._spanProcessor.onEnd(span);
      }
    }
  }

  /**
   * Shuts down the processor. Called when SDK is shut down. This is an
   * opportunity for processor to do any cleanup required.
   */
  async shutdown(): Promise<void> {
    return this._spanProcessor.shutdown();
  }
}

  spanProcessors: [
    new SamplingSpanProcessor(
      new BatchSpanProcessor(traceExporter),
      samplePercentage
    ),
  ],