CloudWatch: Expand alias variables when query yields no result (#22695)

* Return empty time series with expanded aliases in case query yielded no results

* PR feedback

pkg/tsdb/cloudwatch/cloudwatch_query.go

@@ -55,6 +55,22 @@ func (q *cloudWatchQuery) isInferredSearchExpression() bool {
 	return false
 }
 
+func (q *cloudWatchQuery) isMultiValuedDimensionExpression() bool {
+	for _, values := range q.Dimensions {
+		for _, v := range values {
+			if v == "*" {
+				return false
+			}
+		}
+
+		if len(values) > 1 {
+			return true
+		}
+	}
+
+	return false
+}
+
 func (q *cloudWatchQuery) isMetricStat() bool {
 	return !q.isSearchExpression() && !q.isMathExpression()
 }

pkg/tsdb/cloudwatch/cloudwatch_query_test.go

@@ -95,6 +95,29 @@ func TestCloudWatchQuery(t *testing.T) {
 			})
 		})
 
+		Convey("and query has a multi-valued dimension", func() {
+			query := &cloudWatchQuery{
+				RefId:      "A",
+				Region:     "us-east-1",
+				Expression: "",
+				Stats:      "Average",
+				Period:     300,
+				Id:         "id1",
+				Dimensions: map[string][]string{
+					"InstanceId":   {"i-12345678", "i-12345679"},
+					"InstanceType": {"abc"},
+				},
+			}
+
+			Convey("it is a search expression", func() {
+				So(query.isSearchExpression(), ShouldBeTrue)
+			})
+
+			Convey("it is a multi-valued dimension expression", func() {
+				So(query.isMultiValuedDimensionExpression(), ShouldBeTrue)
+			})
+		})
+
 		Convey("and no dimensions were added", func() {
 			query := &cloudWatchQuery{
 				RefId:      "A",

pkg/tsdb/cloudwatch/response_parser.go

@@ -83,17 +83,44 @@ func parseGetMetricDataTimeSeries(metricDataResults map[string]*cloudwatch.Metri
 			}
 		}
 
-		series := tsdb.TimeSeries{
-			Tags:   make(map[string]string),
+		// In case a multi-valued dimension is used and the cloudwatch query yields no values, create one empty time series for each dimension value.
+		// Use that dimension value to expand the alias field
+		if len(metricDataResult.Values) == 0 && query.isMultiValuedDimensionExpression() {
+			series := 0
+			multiValuedDimension := ""
+			for key, values := range query.Dimensions {
+				if len(values) > series {
+					series = len(values)
+					multiValuedDimension = key
+				}
+			}
+
+			for _, value := range query.Dimensions[multiValuedDimension] {
+				emptySeries := tsdb.TimeSeries{
+					Tags:   map[string]string{multiValuedDimension: value},
 					Points: make([]tsdb.TimePoint, 0),
 				}
+				for key, values := range query.Dimensions {
+					if key != multiValuedDimension && len(values) > 0 {
+						emptySeries.Tags[key] = values[0]
+					}
+				}
 
+				emptySeries.Name = formatAlias(query, query.Stats, emptySeries.Tags, label)
+				result = append(result, &emptySeries)
+			}
+		} else {
 			keys := make([]string, 0)
 			for k := range query.Dimensions {
 				keys = append(keys, k)
 			}
 			sort.Strings(keys)
 
+			series := tsdb.TimeSeries{
+				Tags:   make(map[string]string),
+				Points: make([]tsdb.TimePoint, 0),
+			}
+
 			for _, key := range keys {
 				values := query.Dimensions[key]
 				if len(values) == 1 && values[0] != "*" {
@@ -122,6 +149,7 @@ func parseGetMetricDataTimeSeries(metricDataResults map[string]*cloudwatch.Metri
 			}
 			result = append(result, &series)
 		}
+	}
 	return &result, partialData, nil
 }
 
@@ -142,7 +170,7 @@ func formatAlias(query *cloudWatchQuery, stat string, dimensions map[string]stri
 		return query.Id
 	}
 
-	if len(query.Alias) == 0 && query.isInferredSearchExpression() {
+	if len(query.Alias) == 0 && query.isInferredSearchExpression() && !query.isMultiValuedDimensionExpression() {
 		return label
 	}
 

pkg/tsdb/cloudwatch/response_parser_test.go

@@ -189,6 +189,82 @@ func TestCloudWatchResponseParser(t *testing.T) {
 			So((*series)[1].Name, ShouldEqual, "lb4 Expanded")
 		})
 
+		Convey("can expand dimension value when no values are returned and a multi-valued template variabel is used", func() {
+			timestamp := time.Unix(0, 0)
+			resp := map[string]*cloudwatch.MetricDataResult{
+				"lb3": {
+					Id:    aws.String("lb3"),
+					Label: aws.String("lb3"),
+					Timestamps: []*time.Time{
+						aws.Time(timestamp),
+						aws.Time(timestamp.Add(60 * time.Second)),
+						aws.Time(timestamp.Add(180 * time.Second)),
+					},
+					Values:     []*float64{},
+					StatusCode: aws.String("Complete"),
+				},
+			}
+
+			query := &cloudWatchQuery{
+				RefId:      "refId1",
+				Region:     "us-east-1",
+				Namespace:  "AWS/ApplicationELB",
+				MetricName: "TargetResponseTime",
+				Dimensions: map[string][]string{
+					"LoadBalancer": {"lb1", "lb2"},
+				},
+				Stats:  "Average",
+				Period: 60,
+				Alias:  "{{LoadBalancer}} Expanded",
+			}
+			series, partialData, err := parseGetMetricDataTimeSeries(resp, query)
+
+			So(err, ShouldBeNil)
+			So(partialData, ShouldBeFalse)
+			So(len(*series), ShouldEqual, 2)
+			So((*series)[0].Name, ShouldEqual, "lb1 Expanded")
+			So((*series)[1].Name, ShouldEqual, "lb2 Expanded")
+		})
+
+		Convey("can expand dimension value when no values are returned and a multi-valued template variable and two single-valued dimensions are used", func() {
+			timestamp := time.Unix(0, 0)
+			resp := map[string]*cloudwatch.MetricDataResult{
+				"lb3": {
+					Id:    aws.String("lb3"),
+					Label: aws.String("lb3"),
+					Timestamps: []*time.Time{
+						aws.Time(timestamp),
+						aws.Time(timestamp.Add(60 * time.Second)),
+						aws.Time(timestamp.Add(180 * time.Second)),
+					},
+					Values:     []*float64{},
+					StatusCode: aws.String("Complete"),
+				},
+			}
+
+			query := &cloudWatchQuery{
+				RefId:      "refId1",
+				Region:     "us-east-1",
+				Namespace:  "AWS/ApplicationELB",
+				MetricName: "TargetResponseTime",
+				Dimensions: map[string][]string{
+					"LoadBalancer": {"lb1", "lb2"},
+					"InstanceType": {"micro"},
+					"Resource":     {"res"},
+				},
+				Stats:  "Average",
+				Period: 60,
+				Alias:  "{{LoadBalancer}} Expanded {{InstanceType}} - {{Resource}}",
+			}
+			series, partialData, err := parseGetMetricDataTimeSeries(resp, query)
+
+			So(err, ShouldBeNil)
+			So(partialData, ShouldBeFalse)
+			So(len(*series), ShouldEqual, 2)
+			So((*series)[0].Name, ShouldEqual, "lb1 Expanded micro - res")
+			So((*series)[1].Name, ShouldEqual, "lb2 Expanded micro - res")
+		})
+
 		Convey("can parse cloudwatch response", func() {
 			timestamp := time.Unix(0, 0)
 			resp := map[string]*cloudwatch.MetricDataResult{