Fix metric name passed to external scaler in GetMetrics call.

pkg/scalers/external_scaler.go

@@ -198,7 +198,11 @@ func (s *externalScaler) GetMetrics(ctx context.Context, metricName string, metr
 	defer done()
 
 	// Remove the sX- prefix as the external scaler shouldn't have to know about it
-	metricName = strings.SplitN(metricName, "-", 2)[1]
+	metricName, err = GenerateMetricNameWithoutIndex(s.metadata.scalerIndex, metricName)
+	if err != nil {
+		return metrics, err
+	}
+
 	request := &pb.GetMetricsRequest{
 		MetricName:      metricName,
 		ScaledObjectRef: &s.scaledObjectRef,

pkg/scalers/scaler.go

@@ -19,6 +19,7 @@ package scalers
 import (
 	"context"
 	"fmt"
+	"strings"
 	"time"
 
 	"k8s.io/api/autoscaling/v2beta2"
@@ -110,6 +111,21 @@ func GenerateMetricNameWithIndex(scalerIndex int, metricName string) string {
 	return fmt.Sprintf("s%d-%s", scalerIndex, metricName)
 }
 
+// GenerateMetricNameWithoutIndex removes the index prefix from the metric name
+func GenerateMetricNameWithoutIndex(scalerIndex int, metricName string) (string, error) {
+	metricNameSplit := strings.SplitN(metricName, "-", 2)
+	if len(metricNameSplit) != 2 {
+		return "", fmt.Errorf("metric name without index prefix")
+	}
+
+	indexPrefix, metricNameWithoutIndex := metricNameSplit[0], metricNameSplit[1]
+	if indexPrefix != fmt.Sprintf("s%d", scalerIndex) {
+		return "", fmt.Errorf("metric name contains incorrect index prefix")
+	}
+
+	return metricNameWithoutIndex, nil
+}
+
 // GetMetricTargetType helps getting the metric target type of the scaler
 func GetMetricTargetType(config *ScalerConfig) (v2beta2.MetricTargetType, error) {
 	switch config.MetricType {

pkg/scalers/scaler_test.go

@@ -85,3 +85,38 @@ func TestGetMetricTarget(t *testing.T) {
 		})
 	}
 }
+
+func TestGenerateMetricNameWithoutIndex(t *testing.T) {
+	cases := []struct {
+		scalerIndex                          int
+		metricName                           string
+		expectedMetricNameWithoutIndexPrefix string
+		isError                              bool
+	}{
+		// Proper input
+		{scalerIndex: 0, metricName: "s0-metricName", expectedMetricNameWithoutIndexPrefix: "metricName", isError: false},
+		// Incorrect index prefix
+		{scalerIndex: 1, metricName: "s0-metricName", expectedMetricNameWithoutIndexPrefix: "", isError: true},
+		// Incorrect index prefix
+		{scalerIndex: 0, metricName: "0-metricName", expectedMetricNameWithoutIndexPrefix: "", isError: true},
+		// No index prefix
+		{scalerIndex: 0, metricName: "metricName", expectedMetricNameWithoutIndexPrefix: "", isError: true},
+	}
+
+	for _, testCase := range cases {
+		metricName, err := GenerateMetricNameWithoutIndex(testCase.scalerIndex, testCase.metricName)
+		if err != nil && !testCase.isError {
+			t.Error("Expected success but got error", err)
+		}
+
+		if testCase.isError && err == nil {
+			t.Error("Expected error but got success")
+		}
+
+		if err == nil {
+			if metricName != testCase.expectedMetricNameWithoutIndexPrefix {
+				t.Errorf("Expected - %s, Got - %s", testCase.expectedMetricNameWithoutIndexPrefix, metricName)
+			}
+		}
+	}
+}