The AWSOpenTelemetryDistroJs Lambda layer ignores the generic OTEL_EXPORTER_OTLP_ENDPOINT environment variable and defaults to UDP export (X-Ray). Only the signal-specific OTEL_EXPORTER_OTLP_TRACES_ENDPOINT is recognized as a custom endpoint.

This behavior deviates from the OpenTelemetry OTLP Exporter specification, which states that OTEL_EXPORTER_OTLP_ENDPOINT should be used as a fallback when signal-specific endpoints are not set.

Environment

• AWS Region: eu-central-1
• Lambda Runtime: Node.js 22.x (ARM64)
• ADOT Layer: arn:aws:lambda:eu-central-1:615299751070:layer:AWSOpenTelemetryDistroJs:10
• Target: Custom ADOT Collector behind ALB

Configuration That Does NOT Work

environment: {
  AWS_LAMBDA_EXEC_WRAPPER: "/opt/otel-instrument",
  OTEL_SERVICE_NAME: "my-lambda",
  OTEL_TRACES_EXPORTER: "otlp",
  // ❌ Generic endpoint - IGNORED in Lambda environment
  OTEL_EXPORTER_OTLP_ENDPOINT: "http://my-collector:4318",
  OTEL_EXPORTER_OTLP_PROTOCOL: "http/protobuf",
}

Result: Traces are sent via UDP to X-Ray instead of the specified OTLP endpoint.

Configuration That WORKS

environment: {
  AWS_LAMBDA_EXEC_WRAPPER: "/opt/otel-instrument",
  OTEL_SERVICE_NAME: "my-lambda",
  OTEL_TRACES_EXPORTER: "otlp",
  // ✅ Signal-specific endpoint - recognized as custom endpoint
  OTEL_EXPORTER_OTLP_TRACES_ENDPOINT: "http://my-collector:4318/v1/traces",
  OTEL_EXPORTER_OTLP_PROTOCOL: "http/protobuf",
}

Result: Traces are successfully sent to the custom OTLP endpoint.

Root Cause

In aws-opentelemetry-configurator.ts, the hasCustomOtlpTraceEndpoint() function only checks for OTEL_EXPORTER_OTLP_TRACES_ENDPOINT:

function hasCustomOtlpTraceEndpoint() {
  return process.env['OTEL_EXPORTER_OTLP_TRACES_ENDPOINT'] !== undefined;
}

This check is used in configureOtlp() to decide whether to use UDP export in Lambda:

static configureOtlp(): SpanExporter {
  // ...
  if (!hasCustomOtlpTraceEndpoint() && isLambdaEnvironment()) {
    protocol = 'udp';
  }
  // ...
}

When users set OTEL_EXPORTER_OTLP_ENDPOINT (the generic endpoint), the code doesn't recognize it as a custom endpoint and defaults to UDP export.

Workaround

Use OTEL_EXPORTER_OTLP_TRACES_ENDPOINT instead of OTEL_EXPORTER_OTLP_ENDPOINT. Note that when using the signal-specific endpoint, you must include the full path (/v1/traces).