Keep the number of ReplicaSets to a minimum

config/core/configmaps/deployment.yaml

@@ -27,6 +27,7 @@ data:
   # This is the Go import path for the binary that is containerized
   # and substituted here.
   queue-sidecar-image: ko://knative.dev/serving/cmd/queue
+  revisionHistoryLimit: "2"
   _example: |-
     ################################
     #                              #

pkg/deployment/config.go

@@ -19,6 +19,7 @@ package deployment
 import (
 	"errors"
 	"fmt"
+	"strconv"
 	"strings"
 	"time"
 
@@ -241,6 +242,17 @@ func NewConfigFromMap(configMap map[string]string) (*Config, error) {
 			}
 		}
 	}
+
+	if val, ok := configMap["revisionHistoryLimit"]; ok {
+		limit, err := strconv.Atoi(val)
+		if err != nil {
+			return nil, fmt.Errorf("invalid revisionHistoryLimit value %s: %w", val, err)
+		}
+		nc.RevisionHistoryLimit = int32(limit)
+	} else {
+		nc.RevisionHistoryLimit = 2 // Default value if not set
+	}
+
 	return nc, nil
 }
 
@@ -309,4 +321,7 @@ type Config struct {
 
 	// RuntimeClassNames specifies which runtime the Pod will use
 	RuntimeClassNames map[string]RuntimeClassNameLabelSelector
+
+	// RevisionHistoryLimit is the maximum number of old replicas to retain.
+	RevisionHistoryLimit int32
 }

pkg/reconciler/revision/resources/deploy.go

@@ -376,6 +376,12 @@ func MakeDeployment(rev *v1.Revision, cfg *config.Config) (*appsv1.Deployment, e
 	labels := makeLabels(rev)
 	anns := makeAnnotations(rev)
 
+	// Set revisionHistoryLimit from config-deployment.yaml or use default
+	revisionHistoryLimit := int32(cfg.Deployment.RevisionHistoryLimit) // e.g., 2 or 0
+	if revisionHistoryLimit == 0 {
+		revisionHistoryLimit = 2 // Default to 2 if not configured as 0
+	}
+
 	// Slowly but steadily roll the deployment out, to have the least possible impact.
 	maxUnavailable := intstr.FromInt(0)
 	return &appsv1.Deployment{
@@ -390,6 +396,7 @@ func MakeDeployment(rev *v1.Revision, cfg *config.Config) (*appsv1.Deployment, e
 			Replicas:                ptr.Int32(replicaCount),
 			Selector:                makeSelector(rev),
 			ProgressDeadlineSeconds: ptr.Int32(progressDeadline),
+			RevisionHistoryLimit:    ptr.Int32(revisionHistoryLimit),
 			Strategy: appsv1.DeploymentStrategy{
 				Type: appsv1.RollingUpdateDeploymentStrategyType,
 				RollingUpdate: &appsv1.RollingUpdateDeployment{