[Metricbeat] Add dedot for cloudwatch metric name (elastic#15917)

* Add dedot for cloudwatch metric name
* update changelog

CHANGELOG.next.asciidoc

@@ -72,6 +72,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 
 - Add dedot for tags in ec2 metricset and cloudwatch metricset. {issue}15843[15843] {pull}15844[15844]
 - Use RFC3339 format for timestamps collected using the SQL module. {pull}15847[15847]
+- Add dedot for cloudwatch metric name. {issue}15916[15916] {pull}15917[15917]
 
 *Packetbeat*
 

x-pack/metricbeat/module/aws/cloudwatch/cloudwatch.go

@@ -391,7 +391,8 @@ func generateFieldName(namespace string, labels []string) string {
 	// Check if statistic method is one of Sum, SampleCount, Minimum, Maximum, Average
 	// With checkStatistics function, no need to check bool return value here
 	statMethod, _ := statisticLookup(stat)
-	return "aws." + stripNamespace(namespace) + ".metrics." + labels[metricNameIdx] + "." + statMethod
+	// By default, replace dot "." using under bar "_" for metric names
+	return "aws." + stripNamespace(namespace) + ".metrics." + common.DeDot(labels[metricNameIdx]) + "." + statMethod
 }
 
 // stripNamespace converts Cloudwatch namespace into the root field we will use for metrics

x-pack/metricbeat/module/aws/cloudwatch/cloudwatch_test.go

@@ -699,6 +699,12 @@ func TestGenerateFieldName(t *testing.T) {
 			[]string{"CPUUtilization", "AWS/EC2", "p10", "InstanceId", "i-1"},
 			"aws.ec2.metrics.CPUUtilization.p10",
 		},
+		{
+			"test metric name with dot",
+			"cloudwatch",
+			[]string{"DeliveryToS3.Records", "AWS/Firehose", "Average", "DeliveryStreamName", "test-1"},
+			"aws.firehose.metrics.DeliveryToS3_Records.avg",
+		},
 	}
 
 	for _, c := range cases {