Fix EMF exporter to generate EMF metrics when dimensions are empty due to no attributes (#228)

*Description of changes:*
Populate the correct `CloudWatchMetrics` in EMF when metrics has empty
dimension list due to no attributes.

*Testing:*
```json
{
    "_aws": {
        "Timestamp": 1753213216039,
        "CloudWatchMetrics": [
            {
                "Namespace": "default",
                "Metrics": [
                    {
                        "Name": "histogram.counter",
                        "Unit": "Milliseconds"
                    }
                ]
            }
        ]
    },
    "Version": "1",
    "otel.resource.service.name": "unknown_service:node",
    "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.aws.service.type": "gen_ai_agent",
    "histogram.counter": {
        "Values": [
            0.9946140065969877,
            1.9892280131939772,
            3.002072155884692,
            3.978456026387959,
            0
        ],
        "Counts": [
            1,
            1,
            2,
            3,
            2
        ],
        "Count": 9,
        "Sum": 21,
        "Max": 4,
        "Min": 0
    }
}
```

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copy, and redistribute this contribution, under the terms of your
choice.

Author: jj22ee

aws-distro-opentelemetry-node-autoinstrumentation/src/exporter/aws/metrics/aws-cloudwatch-emf-exporter.ts

@@ -71,7 +71,7 @@ interface _Aws {
 
 interface CloudWatchMetric {
   Namespace: string;
-  Dimensions: string[][];
+  Dimensions?: string[][];
   Metrics: Metric[];
 }
 
@@ -449,16 +449,23 @@ export class AWSCloudWatchEMFExporter implements PushMetricExporter {
 
     const dimensionNames = this.getDimensionNames(allAttributes);
 
+    // Add attribute values to the root of the EMF log
     for (const [name, value] of Object.entries(allAttributes)) {
       emfLog[name] = value?.toString() ?? 'undefined';
     }
 
-    if (dimensionNames && metricDefinitions.length > 0) {
-      emfLog._aws.CloudWatchMetrics.push({
+    // Add CloudWatch Metrics if we have metrics, include dimensions only if they exist
+    if (metricDefinitions.length > 0) {
+      const cloudWatchMetric: CloudWatchMetric = {
         Namespace: this.namespace,
-        Dimensions: [dimensionNames],
         Metrics: metricDefinitions,
-      });
+      };
+
+      if (dimensionNames.length > 0) {
+        cloudWatchMetric.Dimensions = [dimensionNames];
+      }
+
+      emfLog._aws.CloudWatchMetrics.push(cloudWatchMetric);
     }
 
     return emfLog;

aws-distro-opentelemetry-node-autoinstrumentation/test/exporter/aws/metrics/aws-cloudwatch-emf-exporter.test.ts

@@ -412,7 +412,7 @@ describe('TestAwsCloudWatchEmfExporter', () => {
 
     expect(result).toHaveProperty('_aws');
     expect(result._aws.CloudWatchMetrics[0].Namespace).toEqual('TestNamespace');
-    expect(result._aws.CloudWatchMetrics[0].Dimensions[0][0]).toEqual('env');
+    expect(result._aws.CloudWatchMetrics[0].Dimensions![0][0]).toEqual('env');
     expect(result._aws.CloudWatchMetrics[0].Metrics[0].Name).toEqual('gauge_metric');
     expect(result._aws.CloudWatchMetrics[0].Metrics[0].Unit).toEqual('Count');
     expect(result._aws.CloudWatchMetrics[0].Metrics[1].Name).toEqual('sum_metric');
@@ -672,10 +672,10 @@ describe('TestAwsCloudWatchEmfExporter', () => {
 
         expect(call1Args.logEvents.length).toEqual(0);
         expect(call2Args.logEvents[0].message).toMatch(
-          /^\{"_aws":\{"Timestamp":\d+,"CloudWatchMetrics":\[\{"Namespace":"TestNamespace","Dimensions":\[\["uniqueKey1"\]\],"Metrics":\[\{"Name":"descriptorName","Unit":"Milliseconds"\}\]\}\]},"Version":"1","descriptorName":3,"uniqueKey1":"uniqueValue1"\}$/
+          /^\{"_aws":\{"Timestamp":\d+,"CloudWatchMetrics":\[\{"Namespace":"TestNamespace","Metrics":\[\{"Name":"descriptorName","Unit":"Milliseconds"\}\],"Dimensions":\[\["uniqueKey1"\]\]\}\]},"Version":"1","descriptorName":3,"uniqueKey1":"uniqueValue1"\}$/
         );
         expect(call3Args.logEvents[0].message).toMatch(
-          /^\{"_aws":\{"Timestamp":\d+,"CloudWatchMetrics":\[\{"Namespace":"TestNamespace","Dimensions":\[\["uniqueKey2"\]\],"Metrics":\[\{"Name":"descriptorName","Unit":"Milliseconds"\}\]\}\]},"Version":"1","descriptorName":9,"uniqueKey2":"uniqueValue2"\}$/
+          /^\{"_aws":\{"Timestamp":\d+,"CloudWatchMetrics":\[\{"Namespace":"TestNamespace","Metrics":\[\{"Name":"descriptorName","Unit":"Milliseconds"\}\],"Dimensions":\[\["uniqueKey2"\]\]\}\]},"Version":"1","descriptorName":9,"uniqueKey2":"uniqueValue2"\}$/
         );
         resolve();
       });
@@ -747,8 +747,42 @@ describe('TestAwsCloudWatchEmfExporter', () => {
     // Check CloudWatch metrics structure
     const cwMetrics = result._aws.CloudWatchMetrics[0];
     expect(cwMetrics.Namespace).toEqual('TestNamespace');
-    expect(cwMetrics.Dimensions[0]).toContain('env');
-    expect(cwMetrics.Dimensions[0]).toContain('service');
+    expect(cwMetrics).toHaveProperty('Dimensions');
+    expect(cwMetrics.Dimensions![0]).toContain('env');
+    expect(cwMetrics.Dimensions![0]).toContain('service');
+    expect(cwMetrics.Metrics[0].Name).toEqual('gauge_metric');
+  });
+
+  it('TestCreateEmfLogWithoutDimensions', () => {
+    /* Test EMF log creation with metrics but no dimensions. */
+    // Create test record with empty attributes (no dimensions)
+    const gaugeRecord: MetricRecord = {
+      ...exporter['createMetricRecord']('gauge_metric', 'Count', 'Gauge', Date.now(), {}),
+      value: 75.0,
+    };
+
+    const records = [gaugeRecord];
+    const resource = new Resource({ 'service.name': 'test-service', 'service.version': '1.0.0' });
+
+    const result = exporter['createEmfLog'](records, resource, 1234567890);
+
+    // Verify EMF log structure
+    expect(result).toHaveProperty('_aws');
+    expect(result._aws).toHaveProperty('CloudWatchMetrics');
+    expect(result._aws.Timestamp).toEqual(1234567890);
+    expect(result.Version).toEqual('1');
+
+    // Check resource attributes are prefixed
+    expect(result['otel.resource.service.name']).toEqual('test-service');
+    expect(result['otel.resource.service.version']).toEqual('1.0.0');
+
+    // Check metric value
+    expect(result.gauge_metric).toEqual(75.0);
+
+    // Check CloudWatch metrics structure
+    const cwMetrics = result._aws.CloudWatchMetrics[0];
+    expect(cwMetrics.Namespace).toEqual('TestNamespace');
+    expect(cwMetrics).not.toHaveProperty('Dimensions');
     expect(cwMetrics.Metrics[0].Name).toEqual('gauge_metric');
   });