Kafka scaler: batch GetOffset requests

CHANGELOG.md

@@ -32,6 +32,7 @@
 - Allow influxdb `authToken`, `serverURL`, and `organizationName` to be sourced from `(Cluster)TriggerAuthentication` ([#1904](https://github.com/kedacore/keda/pull/1904))
 - IBM MQ scaler password handling fix ([#1939](https://github.com/kedacore/keda/pull/1939))
 - Metrics APIServer: Add ratelimiting parameters to override client ([#1944](https://github.com/kedacore/keda/pull/1944))
+- Optimize KafkaScaler by fetching all topic offsets using a single HTTP request ([#1956](https://github.com/kedacore/keda/pull/1956))
 
 ### Breaking Changes
 

pkg/scalers/kafka_scaler.go

@@ -217,8 +217,13 @@ func (s *kafkaScaler) IsActive(ctx context.Context) (bool, error) {
 		return false, err
 	}
 
+	topicOffsets, err := s.getTopicOffsets(partitions)
+	if err != nil {
+		return false, err
+	}
+
 	for _, partition := range partitions {
-		lag, err := s.getLagForPartition(partition, offsets)
+		lag, err := s.getLagForPartition(partition, offsets, topicOffsets)
 		if err != nil && lag == invalidOffset {
 			return true, nil
 		}
@@ -312,7 +317,7 @@ func (s *kafkaScaler) getOffsets(partitions []int32) (*sarama.OffsetFetchRespons
 	return offsets, nil
 }
 
-func (s *kafkaScaler) getLagForPartition(partition int32, offsets *sarama.OffsetFetchResponse) (int64, error) {
+func (s *kafkaScaler) getLagForPartition(partition int32, offsets *sarama.OffsetFetchResponse, topicOffsets map[int32]int64) (int64, error) {
 	block := offsets.GetBlock(s.metadata.topic, partition)
 	if block == nil {
 		kafkaLog.Error(fmt.Errorf("error finding offset block for topic %s and partition %d", s.metadata.topic, partition), "")
@@ -323,11 +328,8 @@ func (s *kafkaScaler) getLagForPartition(partition int32, offsets *sarama.Offset
 		kafkaLog.V(0).Info(fmt.Sprintf("invalid offset found for topic %s in group %s and partition %d, probably no offset is committed yet", s.metadata.topic, s.metadata.group, partition))
 		return invalidOffset, fmt.Errorf("invalid offset found for topic %s in group %s and partition %d, probably no offset is committed yet", s.metadata.topic, s.metadata.group, partition)
 	}
-	latestOffset, err := s.client.GetOffset(s.metadata.topic, partition, sarama.OffsetNewest)
-	if err != nil {
-		kafkaLog.Error(err, fmt.Sprintf("error finding latest offset for topic %s and partition %d\n", s.metadata.topic, partition))
-		return 0, fmt.Errorf("error finding latest offset for topic %s and partition %d", s.metadata.topic, partition)
-	}
+
+	latestOffset := topicOffsets[partition]
 	if consumerOffset == invalidOffset && s.metadata.offsetResetPolicy == earliest {
 		return latestOffset, nil
 	}
@@ -372,9 +374,14 @@ func (s *kafkaScaler) GetMetrics(ctx context.Context, metricName string, metricS
 		return []external_metrics.ExternalMetricValue{}, err
 	}
 
+	topicOffsets, err := s.getTopicOffsets(partitions)
+	if err != nil {
+		return []external_metrics.ExternalMetricValue{}, err
+	}
+
 	totalLag := int64(0)
 	for _, partition := range partitions {
-		lag, _ := s.getLagForPartition(partition, offsets)
+		lag, _ := s.getLagForPartition(partition, offsets, topicOffsets)
 
 		totalLag += lag
 	}
@@ -396,3 +403,51 @@ func (s *kafkaScaler) GetMetrics(ctx context.Context, metricName string, metricS
 
 	return append([]external_metrics.ExternalMetricValue{}, metric), nil
 }
+
+func (s *kafkaScaler) getTopicOffsets(partitions []int32) (map[int32]int64, error) {
+	version := int16(0)
+	if s.client.Config().Version.IsAtLeast(sarama.V0_10_1_0) {
+		version = 1
+	}
+
+	// Step 1: build one OffsetRequest instance per broker.
+	requests := make(map[*sarama.Broker]*sarama.OffsetRequest)
+
+	for _, partitionID := range partitions {
+		broker, err := s.client.Leader(s.metadata.topic, partitionID)
+		if err != nil {
+			return nil, err
+		}
+
+		request, ok := requests[broker]
+		if !ok {
+			request = &sarama.OffsetRequest{Version: version}
+			requests[broker] = request
+		}
+
+		request.AddBlock(s.metadata.topic, partitionID, sarama.OffsetNewest, 1)
+	}
+
+	offsets := make(map[int32]int64)
+
+	// Step 2: send requests, one per broker, and collect offsets
+	for broker, request := range requests {
+		response, err := broker.GetAvailableOffsets(request)
+
+		if err != nil {
+			return nil, err
+		}
+
+		for _, blocks := range response.Blocks {
+			for partitionID, block := range blocks {
+				if block.Err != sarama.ErrNoError {
+					return nil, block.Err
+				}
+
+				offsets[partitionID] = block.Offset
+			}
+		}
+	}
+
+	return offsets, nil
+}