Undici spans appear as UnknownRemoteService in AWS X-Ray when using ADOT Lambda JS layer

[okoseisback]

Describe the question

I'm using the AWS Distro for OpenTelemetry (ADOT) Lambda layer with Node.js 22.x and the built-in Undici Fetch API (since Node.js 18+).
The instrumentation works correctly — spans are created and sent to AWS X-Ray — but all Undici spans appear with placeholder names and attributes such as:

"name": "UnknownRemoteService",
"aws.remote.service": "UnknownRemoteService",
"aws.remote.operation": "UnknownRemoteOperation"

I attempted to fix this by providing a custom Collector config via
OPENTELEMETRY_COLLECTOR_CONFIG_URI = s3://<bucket_name>/otel/collector_config.yaml
and adding a transform processor to rewrite the span name and attributes.
However, based on [issue #2300](aws-observability/aws-otel-collector#2300), it seems the ``** processor** may not be supported in the Lambda environment.

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Steps to reproduce

1. Deploy a Node.js 22.x Lambda function using the AWSOpenTelemetryDistroJs layer.

2. Set environment variables:

   AWS_LAMBDA_EXEC_WRAPPER=/opt/otel-instrument
   OTEL_AWS_APPLICATION_SIGNALS_ENABLED=true
   OTEL_METRICS_EXPORTER=none
   OTEL_NODE_ENABLED_INSTRUMENTATIONS=aws-sdk,aws-lambda,http,undici
   OPENTELEMETRY_COLLECTOR_CONFIG_URI=s3://<bucket_name>/otel/collector_config.yaml

3. In the function code, make a simple Fetch request:

   await fetch("https://example.execute-api.eu-central-1.amazonaws.com/dev/test");

4. Observe the resulting trace in AWS X-Ray — the subsegment for the fetch() call shows as UnknownRemoteService.

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What did you expect to see?

Meaningful span names and attributes similar to AWS SDK instrumentations, for example:

"name": "example.execute-api.eu-central-1.amazonaws.com:443",
"aws.remote.service": "example.execute-api.eu-central-1.amazonaws.com:443",
"aws.remote.operation": "GET /dev/test"

---

Environment

• Runtime: Node.js 22.x (AWS Lambda managed runtime)
• ADOT Layer: AWSOpenTelemetryDistroJs (latest as of Oct 2025)
• Collector Config: Loaded from S3 (s3://<bucket_name>/otel/collector_config.yaml)
• Region: eu-central-1
• Enabled Instrumentations: aws-sdk, aws-lambda, http, undici

---

Collector Config (simplified)

receivers:
  otlp:
    protocols:
      http: {}
      grpc: {}

processors:
  transform/fix-unknown:
    error_mode: ignore
    trace_statements:
      - context: span
        conditions:
          - name == "UnknownRemoteService"
        statements:
          - set(name, Concat(attributes["server.address"], ":", attributes["server.port"]))
          - set(attributes["aws.remote.service"], name)
          - set(attributes["aws.remote.operation"], Concat(attributes["http.request.method"], " ", attributes["url.path"]))

exporters:
  awsxray: {}

service:
  pipelines:
    traces:
      receivers: [otlp]
      processors: [transform/fix-unknown]
      exporters: [awsxray]

---

Additional context

• The same configuration works fine with the standalone ADOT Collector (e.g., on ECS or EKS).
• Within the Lambda ADOT layer, Undici spans remain labeled as UnknownRemoteService.
• AWS SDK spans are named properly (sns.eu-central-1.amazonaws.com:443 etc.), so only Undici appears affected.
• If the transform processor is not supported in the Lambda build, is there any recommended or supported way (e.g. span or attributes processor) to modify span names for Undici/FETCH calls?

Would appreciate any guidance or confirmation about whether this is expected behavior, or if a configuration-based workaround exists.