Support export OTel metrics to be EMF in Standard Output in Lambda (#231)

*Issue #, if available:*
- Currently, ADOT cannot exports metrics in AWS Lambda environment
because Lambda freezes the execution environment asap after invocation.
- The existing EMF Exporter only outputs to CW Logs

*Description of changes:*
- Sync AWS Lambda patch to forceFlush metrics after Lambda function
invocation.
- Introduce ConsoleEMFExporter, which exports OTel metrics to standard
output using the CloudWatch Embedded Metric Format (EMF). In the Lambda
environment, logs written to standard output are automatically forwarded
to CloudWatch by Lambda's built-in logging agent, so this is an
efficient way to export OTel metrics in Lambda to CW as EMF.

*Testing:*
```
START RequestId: fc230af0-020a-429b-8a3d-b7c0a011a777 Version: $LATEST
{"level":50,"time":1753469912921,"pid":2,"hostname":"169.254.67.97","msg":"/histogram endpoint 0"}
2025-07-25T18:58:33.141Z	fc230af0-020a-429b-8a3d-b7c0a011a777	INFO	{"_aws":{"Timestamp":1753469913043,"CloudWatchMetrics":[{"Namespace":"test_adot_namespace2","Metrics":[{"Name":"histogram.counter","Unit":"Milliseconds"}],"Dimensions":[["histogramKey1","histogramKey2"]]}]},"Version":"1","otel.resource.service.name":"adot-lambda-logs-emf-support-testing","otel.resource.telemetry.sdk.language":"nodejs","otel.resource.telemetry.sdk.name":"opentelemetry","otel.resource.telemetry.sdk.version":"1.30.1","otel.resource.telemetry.auto.version":"0.6.0-dev0-aws","otel.resource.cloud.region":"us-west-1","otel.resource.cloud.provider":"aws","otel.resource.faas.name":"adot-lambda-logs-emf-support-testing","otel.resource.faas.version":"$LATEST","otel.resource.faas.instance":"2025/07/25/[$LATEST]990958db5577472a8b72f185f040b136","otel.resource.aws.log.group.names":"/aws/lambda/adot-lambda-logs-emf-support-testing","histogram.counter":{"Values":[2.997969481393705,3.9945921121710146,0],"Counts":[1,2,2],"Count":5,"Sum":11,"Max":4,"Min":0},"histogramKey1":"histogramValue1","histogramKey2":"histogramValue2"}
END RequestId: fc230af0-020a-429b-8a3d-b7c0a011a777
REPORT RequestId: fc230af0-020a-429b-8a3d-b7c0a011a777	Duration: 399.18 ms	Billed Duration: 400 ms	Memory Size: 128 MB	Max Memory Used: 127 MB	Init Duration: 1426.89 ms	
XRAY TraceId: 1-6883d3d7-48a03512232241fa27fe6529	SegmentId: ed5a5f628350482b	Sampled: true	
```

By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice.

Author: jj22ee

aws-distro-opentelemetry-node-autoinstrumentation/src/aws-opentelemetry-configurator.ts

@@ -80,6 +80,8 @@ import { BaggageSpanProcessor } from '@opentelemetry/baggage-span-processor';
 import { logs } from '@opentelemetry/api-logs';
 import { AWS_ATTRIBUTE_KEYS } from './aws-attribute-keys';
 import { AwsCloudWatchOtlpBatchLogRecordProcessor } from './exporter/otlp/aws/logs/aws-cw-otlp-batch-log-record-processor';
+import { ConsoleEMFExporter } from './exporter/aws/metrics/console-emf-exporter';
+import { EMFExporterBase } from './exporter/aws/metrics/emf-exporter-base';
 
 const AWS_TRACES_OTLP_ENDPOINT_PATTERN = '^https://xray\\.([a-z0-9-]+)\\.amazonaws\\.com/v1/traces$';
 const AWS_LOGS_OTLP_ENDPOINT_PATTERN = '^https://logs\\.([a-z0-9-]+)\\.amazonaws\\.com/v1/logs$';
@@ -382,14 +384,17 @@ export class AwsOpentelemetryConfigurator {
   }
 
   private customizeMetricReader(isEmfEnabled: boolean) {
+    let exporter: PushMetricExporter | undefined = undefined;
+
     if (isEmfEnabled) {
-      const emfExporter = createEmfExporter();
-      if (emfExporter) {
-        const periodicExportingMetricReader = new PeriodicExportingMetricReader({
-          exporter: emfExporter,
-        });
-        this.metricReader = periodicExportingMetricReader;
-      }
+      exporter = createEmfExporter();
+    }
+
+    if (exporter) {
+      const periodicExportingMetricReader = new PeriodicExportingMetricReader({
+        exporter: exporter,
+      });
+      this.metricReader = periodicExportingMetricReader;
     }
   }
 
@@ -523,8 +528,7 @@ export class AwsLoggerProcessorProvider {
     return exporters.map(exporter => {
       if (exporter instanceof ConsoleLogRecordExporter) {
         return new SimpleLogRecordProcessor(exporter);
-      }
-      if (exporter instanceof OTLPAwsLogExporter && isAgentObservabilityEnabled()) {
+      } else if (exporter instanceof OTLPAwsLogExporter && isAgentObservabilityEnabled()) {
         return new AwsCloudWatchOtlpBatchLogRecordProcessor(exporter);
       }
       return new BatchLogRecordProcessor(exporter);
@@ -961,15 +965,17 @@ export function validateAndFetchLogsHeader(): OtlpLogHeaderSetting {
   const logHeaders = process.env.OTEL_EXPORTER_OTLP_LOGS_HEADERS;
 
   if (!logHeaders) {
-    diag.warn(
-      'Missing required configuration: The environment variable OTEL_EXPORTER_OTLP_LOGS_HEADERS must be set with ' +
-        `required headers ${AWS_OTLP_LOGS_GROUP_HEADER} and ${AWS_OTLP_LOGS_STREAM_HEADER}. ` +
-        `Example: OTEL_EXPORTER_OTLP_LOGS_HEADERS="${AWS_OTLP_LOGS_GROUP_HEADER}=my-log-group,${AWS_OTLP_LOGS_STREAM_HEADER}=my-log-stream"`
-    );
+    if (!isLambdaEnvironment()) {
+      diag.warn(
+        'Missing required configuration: The environment variable OTEL_EXPORTER_OTLP_LOGS_HEADERS must be set with ' +
+          `required headers ${AWS_OTLP_LOGS_GROUP_HEADER} and ${AWS_OTLP_LOGS_STREAM_HEADER}. ` +
+          `Example: OTEL_EXPORTER_OTLP_LOGS_HEADERS="${AWS_OTLP_LOGS_GROUP_HEADER}=my-log-group,${AWS_OTLP_LOGS_STREAM_HEADER}=my-log-stream"`
+      );
+    }
     return {
-      logGroup: '',
-      logStream: '',
-      namespace: '',
+      logGroup: undefined,
+      logStream: undefined,
+      namespace: undefined,
       isValid: false,
     };
   }
@@ -1030,16 +1036,27 @@ export function checkEmfExporterEnabled(): boolean {
   return true;
 }
 
-export function createEmfExporter(): AWSCloudWatchEMFExporter | undefined {
-  const headersResult = validateAndFetchLogsHeader();
-  if (!headersResult.isValid) {
-    return undefined;
+/**
+ * Create the appropriate EMF exporter based on the environment and configuration.
+ *
+ * @returns {EMFExporterBase | undefined}
+ */
+export function createEmfExporter(): EMFExporterBase | undefined {
+  let exporter: EMFExporterBase | undefined = undefined;
+  const otlpLogHeaderSetting = validateAndFetchLogsHeader();
+
+  if (isLambdaEnvironment() && !otlpLogHeaderSetting.isValid) {
+    // Lambda without valid logs http headers - use Console EMF exporter
+    exporter = new ConsoleEMFExporter(otlpLogHeaderSetting.namespace);
+  } else if (otlpLogHeaderSetting.isValid) {
+    // Non-Lambda environment - use CloudWatch EMF exporter
+    // If headersResult.isValid is true, then headersResult.logGroup and headersResult.logStream are guaranteed to be strings
+    exporter = new AWSCloudWatchEMFExporter(
+      otlpLogHeaderSetting.namespace,
+      otlpLogHeaderSetting.logGroup as string,
+      otlpLogHeaderSetting.logStream as string
+    );
   }
 
-  // If headersResult.isValid is true, then headersResult.logGroup and headersResult.logStream are guaranteed to be strings
-  return new AWSCloudWatchEMFExporter(
-    headersResult.namespace,
-    headersResult.logGroup as string,
-    headersResult.logStream as string
-  );
+  return exporter;
 }