Adding Lag-dependent implementation of Redis streams scaler

CHANGELOG.md

@@ -48,7 +48,8 @@ To learn more about active deprecations, we recommend checking [GitHub Discussio
 
 - **CPU/Memory scaler**: Add support for scale to zero if there are multiple triggers([#4269](https://github.com/kedacore/keda/issues/4269))
 - **Redis Scalers**: Allow scaling using redis stream length ([#4277](https://github.com/kedacore/keda/issues/4277))
-- **General**: Introduce new Solr Scaler ([#4234](https://github.com/kedacore/keda/issues/4234))
+- **Redis Scalers**: Allow scaling using consumer group lag ([#3127](https://github.com/kedacore/keda/issues/3127))
+- **General:** Introduce new Solr Scaler ([#4234](https://github.com/kedacore/keda/issues/4234))
 
 ### Improvements
 

pkg/scalers/redis_streams_scaler.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"strconv"
+	"strings"
 
 	"github.com/go-logr/logr"
 	"github.com/redis/go-redis/v9"
@@ -19,22 +20,27 @@ type scaleFactor int8
 const (
 	xPendingFactor scaleFactor = iota + 1
 	xLengthFactor
+	lagFactor
 )
 
 const (
 	// defaults
-	defaultDBIndex       = 0
-	defaultTargetEntries = 5
+	defaultDBIndex             = 0
+	defaultTargetEntries       = 5
+	defaultTargetLag           = 5
+	defaultActivationTargetLag = 0
 
 	// metadata names
-	pendingEntriesCountMetadata = "pendingEntriesCount"
-	streamLengthMetadata        = "streamLength"
-	streamNameMetadata          = "stream"
-	consumerGroupNameMetadata   = "consumerGroup"
-	usernameMetadata            = "username"
-	passwordMetadata            = "password"
-	databaseIndexMetadata       = "databaseIndex"
-	enableTLSMetadata           = "enableTLS"
+	lagMetadata                      = "lagCount"
+	pendingEntriesCountMetadata      = "pendingEntriesCount"
+	streamLengthMetadata             = "streamLength"
+	streamNameMetadata               = "stream"
+	consumerGroupNameMetadata        = "consumerGroup"
+	usernameMetadata                 = "username"
+	passwordMetadata                 = "password"
+	databaseIndexMetadata            = "databaseIndex"
+	enableTLSMetadata                = "enableTLS"
+	activationValueTriggerConfigName = "activationTargetLag"
 )
 
 type redisStreamsScaler struct {
@@ -49,11 +55,13 @@ type redisStreamsMetadata struct {
 	scaleFactor               scaleFactor
 	targetPendingEntriesCount int64
 	targetStreamLength        int64
+	targetLag                 int64
 	streamName                string
 	consumerGroupName         string
 	databaseIndex             int
 	connectionInfo            redisConnectionInfo
 	scalerIndex               int
+	activationTargetLag       int64
 }
 
 // NewRedisStreamsScaler creates a new redisStreamsScaler
@@ -87,6 +95,7 @@ func NewRedisStreamsScaler(ctx context.Context, isClustered, isSentinel bool, co
 
 func createClusteredRedisStreamsScaler(ctx context.Context, meta *redisStreamsMetadata, metricType v2.MetricTargetType, logger logr.Logger) (Scaler, error) {
 	client, err := getRedisClusterClient(ctx, meta.connectionInfo)
+
 	if err != nil {
 		return nil, fmt.Errorf("connection to redis cluster failed: %w", err)
 	}
@@ -166,6 +175,76 @@ func createEntriesCountFn(client redis.Cmdable, meta *redisStreamsMetadata) (ent
 			}
 			return entriesLength, nil
 		}
+	case lagFactor:
+		entriesCountFn = func(ctx context.Context) (int64, error) {
+			// Make sure that redis is version 7+, which is required for xinfo lag
+			info, err := client.Info(ctx).Result()
+			if err != nil {
+				err := errors.New("could not find Redis version")
+				return -1, err
+			}
+			infoLines := strings.Split(info, "\n")
+			versionFound := false
+			for i := 0; i < len(infoLines); i++ {
+				line := infoLines[i]
+				lineSplit := strings.Split(line, ":")
+				if len(lineSplit) > 1 {
+					fieldName := lineSplit[0]
+					fieldValue := lineSplit[1]
+					if fieldName == "redis_version" {
+						versionFound = true
+						versionNumString := strings.Split(fieldValue, ".")[0]
+						versionNum, err := strconv.ParseInt(versionNumString, 10, 64)
+						if err != nil {
+							err := errors.New("redis version could not be converted to number")
+							return -1, err
+						}
+						if versionNum < int64(7) {
+							err := errors.New("redis version 7+ required for lag")
+							return -1, err
+						}
+						break
+					}
+				}
+			}
+			if !versionFound {
+				err := errors.New("could not find Redis version number")
+				return -1, err
+			}
+			groups, err := client.XInfoGroups(ctx, meta.streamName).Result()
+
+			// If XINFO GROUPS can't find the stream key, it hasn't been created
+			// yet. In that case, we return a lag of 0.
+			if fmt.Sprint(err) == "ERR no such key" {
+				return 0, nil
+			}
+
+			// If the stream has been created, then we find the consumer group
+			// associated with this scaler and return its lag.
+			numGroups := len(groups)
+			for i := 0; i < numGroups; i++ {
+				group := groups[i]
+				if group.Name == meta.consumerGroupName {
+					return int64(group.Lag), nil
+				}
+			}
+
+			// There is an edge case where the Redis producer has set up the
+			// stream [meta.streamName], but the consumer group [meta.consumerGroupName]
+			// for that stream isn't registered with Redis. In other words, the
+			// producer has created messages for the stream, but the consumer group
+			// hasn't yet registered itself on Redis because scaling starts with 0
+			// consumers. In this case, it's necessary to use XLEN to return what
+			// the lag would have been if the consumer group had been created since
+			// it's not possible to obtain the lag for a nonexistent consumer
+			// group. From here, the consumer group gets instantiated, and scaling
+			// again occurs according to XINFO GROUP lag.
+			entriesLength, err := client.XLen(ctx, meta.streamName).Result()
+			if err != nil {
+				return -1, err
+			}
+			return entriesLength, nil
+		}
 	default:
 		err = fmt.Errorf("unrecognized scale factor %v", meta.scaleFactor)
 	}
@@ -210,16 +289,38 @@ func parseRedisStreamsMetadata(config *ScalerConfig, parseFn redisAddressParser)
 		return nil, ErrRedisMissingStreamName
 	}
 
+	meta.activationTargetLag = defaultActivationTargetLag
+
 	if val, ok := config.TriggerMetadata[consumerGroupNameMetadata]; ok {
 		meta.consumerGroupName = val
-		meta.scaleFactor = xPendingFactor
-		meta.targetPendingEntriesCount = defaultTargetEntries
-		if val, ok := config.TriggerMetadata[pendingEntriesCountMetadata]; ok {
-			pendingEntriesCount, err := strconv.ParseInt(val, 10, 64)
+		if val, ok := config.TriggerMetadata[lagMetadata]; ok {
+			meta.scaleFactor = lagFactor
+			lag, err := strconv.ParseInt(val, 10, 64)
 			if err != nil {
-				return nil, fmt.Errorf("error parsing pending entries count: %w", err)
+				return nil, fmt.Errorf("error parsing lag: %w", err)
+			}
+			meta.targetLag = lag
+
+			if val, ok := config.TriggerMetadata[activationValueTriggerConfigName]; ok {
+				activationVal, err := strconv.ParseInt(val, 10, 64)
+				if err != nil {
+					return nil, errors.New("error while parsing activation lag value")
+				}
+				meta.activationTargetLag = activationVal
+			} else {
+				err := errors.New("activationTargetLag required for Redis lag")
+				return nil, err
+			}
+		} else {
+			meta.scaleFactor = xPendingFactor
+			meta.targetPendingEntriesCount = defaultTargetEntries
+			if val, ok := config.TriggerMetadata[pendingEntriesCountMetadata]; ok {
+				pendingEntriesCount, err := strconv.ParseInt(val, 10, 64)
+				if err != nil {
+					return nil, fmt.Errorf("error parsing pending entries count: %w", err)
+				}
+				meta.targetPendingEntriesCount = pendingEntriesCount
 			}
-			meta.targetPendingEntriesCount = pendingEntriesCount
 		}
 	} else {
 		meta.scaleFactor = xLengthFactor
@@ -259,6 +360,8 @@ func (s *redisStreamsScaler) GetMetricSpecForScaling(context.Context) []v2.Metri
 		metricValue = s.metadata.targetPendingEntriesCount
 	case xLengthFactor:
 		metricValue = s.metadata.targetStreamLength
+	case lagFactor:
+		metricValue = s.metadata.targetLag
 	}
 
 	externalMetric := &v2.ExternalMetricSource{
@@ -271,16 +374,15 @@ func (s *redisStreamsScaler) GetMetricSpecForScaling(context.Context) []v2.Metri
 	return []v2.MetricSpec{metricSpec}
 }
 
-// GetMetricsAndActivity fetches the number of pending entries for a consumer group in a stream
+// GetMetricsAndActivity fetches the metric value for a consumer group in a stream
 func (s *redisStreamsScaler) GetMetricsAndActivity(ctx context.Context, metricName string) ([]external_metrics.ExternalMetricValue, bool, error) {
-	pendingEntriesCount, err := s.getEntriesCountFn(ctx)
+	metricCount, err := s.getEntriesCountFn(ctx)
 
 	if err != nil {
-		s.logger.Error(err, "error fetching pending entries count")
+		s.logger.Error(err, "error fetching metric count")
 		return []external_metrics.ExternalMetricValue{}, false, err
 	}
 
-	metric := GenerateMetricInMili(metricName, float64(pendingEntriesCount))
-
-	return []external_metrics.ExternalMetricValue{metric}, pendingEntriesCount > 0, nil
+	metric := GenerateMetricInMili(metricName, float64(metricCount))
+	return []external_metrics.ExternalMetricValue{metric}, int64(metricCount) > s.metadata.activationTargetLag, nil
 }