fix(detectors/aws/lambda): return nil error when not running on Lambda

CHANGELOG.md

@@ -17,6 +17,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - Report `ot-baggage-*` extraction errors from `go.opentelemetry.io/contrib/propagators/ot` to `otel.Handle` instead of silently discarding them, while still attaching the successfully parsed baggage members to the context. (#9395)
 - Set `error.type` on the `rpc.client.call.duration` and `rpc.server.call.duration` metrics in `go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc` when the RPC fails with a non-OK status, per the RPC semantic conventions. (#9429)
 - Reject OTLP exporter headers with an empty `name` in `go.opentelemetry.io/contrib/otelconf`, `go.opentelemetry.io/contrib/otelconf/x`, and `go.opentelemetry.io/contrib/otelconf/v0.3.0`, instead of forwarding invalid header names to OTLP exporters. (#9102)
+- `go.opentelemetry.io/contrib/detectors/aws/lambda` no longer returns an error when run outside of an AWS Lambda environment, matching the no-op behavior of other resource detectors.
 
 <!-- Released section -->
 <!-- Don't change this section unless doing release -->

detectors/aws/lambda/detector.go

@@ -6,7 +6,6 @@ package lambda
 
 import (
 	"context"
-	"errors"
 	"os"
 	"strconv"
 
@@ -26,10 +25,7 @@ const (
 	miB                         = 1 << 20
 )
 
-var (
-	empty          = resource.Empty()
-	errNotOnLambda = errors.New("process is not on Lambda, cannot detect environment variables from Lambda")
-)
+var empty = resource.Empty()
 
 // resource detector collects resource information from Lambda environment.
 type resourceDetector struct{}
@@ -47,7 +43,7 @@ func (*resourceDetector) Detect(context.Context) (*resource.Resource, error) {
 	// Lambda resources come from ENV
 	lambdaName := os.Getenv(lambdaFunctionNameEnvVar)
 	if lambdaName == "" {
-		return empty, errNotOnLambda
+		return empty, nil
 	}
 	awsRegion := os.Getenv(awsRegionEnvVar)
 	functionVersion := os.Getenv(lambdaFunctionVersionEnvVar)

detectors/aws/lambda/detector_test.go

@@ -37,12 +37,12 @@ func TestDetectSuccess(t *testing.T) {
 	assert.Equal(t, expectedResource, res, "Resource returned is incorrect")
 }
 
-// return empty resource when not running on lambda.
+// return empty resource and no error when not running on lambda.
 func TestReturnsIfNoEnvVars(t *testing.T) {
 	os.Clearenv()
 	detector := resourceDetector{}
 	res, err := detector.Detect(t.Context())
 
-	assert.Equal(t, errNotOnLambda, err)
+	assert.NoError(t, err, "Detector unexpectedly returned error when not running on Lambda")
 	assert.Empty(t, res.Attributes())
 }