Add default cluster-side min-scale

config/core/configmaps/autoscaler.yaml

@@ -23,7 +23,7 @@ metadata:
     app.kubernetes.io/version: devel
     serving.knative.dev/release: devel
   annotations:
-    knative.dev/example-checksum: "604cb513"
+    knative.dev/example-checksum: "b4401cf4"
 data:
   _example: |
     ################################
@@ -187,6 +187,10 @@ data:
     # or the "autoscaling.knative.dev/initialScale" annotation, can be set to 0.
     allow-zero-initial-scale: "false"
 
+    # min-scale is the cluster-wide default value for the min scale of a revision,
+    # unless overridden by the "autoscaling.knative.dev/minScale" annotation.
+    min-scale: "0"
+
     # max-scale is the cluster-wide default value for the max scale of a revision,
     # unless overridden by the "autoscaling.knative.dev/maxScale" annotation.
     # If set to 0, the revision has no maximum scale.

pkg/apis/autoscaling/v1alpha1/pa_lifecycle.go

@@ -86,7 +86,10 @@ func (pa *PodAutoscaler) annotationFloat64(key string) (float64, bool) {
 func (pa *PodAutoscaler) ScaleBounds(asConfig *autoscalerconfig.Config) (int32, int32) {
 	var min int32
 	if pa.Spec.Reachability != ReachabilityUnreachable {
-		min, _ = pa.annotationInt32(autoscaling.MinScaleAnnotationKey)
+		min = asConfig.MinScale
+		if paMin, ok := pa.annotationInt32(autoscaling.MinScaleAnnotationKey); ok {
+			min = paMin
+		}
 	}
 
 	max := asConfig.MaxScale

pkg/apis/autoscaling/v1alpha1/pa_lifecycle_test.go

@@ -596,6 +596,13 @@ func TestScaleBounds(t *testing.T) {
 		max:     "sandwich",
 		wantMin: 0,
 		wantMax: 0,
+	}, {
+		name: "min-scale set but unreachable",
+		config: autoscalerconfig.Config{
+			MinScale: 2,
+		},
+		reachability: ReachabilityUnreachable,
+		wantMin:      0,
 	}}
 
 	for _, tc := range cases {

pkg/autoscaler/config/autoscalerconfig/autoscalerconfig.go

@@ -50,6 +50,10 @@ type Config struct {
 	// services. This can be set to 0 iff AllowZeroInitialScale is true.
 	InitialScale int32
 
+	// MinScale is the default min scale for any revision created without an
+	// autoscaling.knative.dev/minScale annotation
+	MinScale int32
+
 	// MaxScale is the default max scale for any revision created without an
 	// autoscaling.knative.dev/maxScale annotation
 	MaxScale int32

pkg/autoscaler/config/config.go

@@ -60,6 +60,7 @@ func defaultConfig() *autoscalerconfig.Config {
 		PodAutoscalerClass:            autoscaling.KPA,
 		AllowZeroInitialScale:         false,
 		InitialScale:                  1,
+		MinScale:                      0,
 		MaxScale:                      0,
 		MaxScaleLimit:                 0,
 	}
@@ -86,6 +87,7 @@ func NewConfigFromMap(data map[string]string) (*autoscalerconfig.Config, error)
 		cm.AsFloat64("panic-threshold-percentage", &lc.PanicThresholdPercentage),
 
 		cm.AsInt32("initial-scale", &lc.InitialScale),
+		cm.AsInt32("min-scale", &lc.MinScale),
 		cm.AsInt32("max-scale", &lc.MaxScale),
 		cm.AsInt32("max-scale-limit", &lc.MaxScaleLimit),
 
@@ -176,6 +178,10 @@ func validate(lc *autoscalerconfig.Config) (*autoscalerconfig.Config, error) {
 		return nil, fmt.Errorf("initial-scale = %v, must be at least 0 (or at least 1 when allow-zero-initial-scale is false)", lc.InitialScale)
 	}
 
+	if lc.MinScale < 0 {
+		return nil, fmt.Errorf("min-scale = %v, must be at least 0", lc.MinScale)
+	}
+
 	var minMaxScale int32
 	if lc.MaxScaleLimit > 0 {
 		// Default maxScale must be set if maxScaleLimit is set.
@@ -191,6 +197,10 @@ func validate(lc *autoscalerconfig.Config) (*autoscalerconfig.Config, error) {
 		return nil, fmt.Errorf("max-scale-limit = %v, must be at least 0", lc.MaxScaleLimit)
 	}
 
+	if lc.MinScale > lc.MaxScale && lc.MaxScale > 0 {
+		return nil, fmt.Errorf("min-scale (%d) must be less than max-scale (%d)", lc.MinScale, lc.MaxScale)
+	}
+
 	return lc, nil
 }
 

pkg/autoscaler/config/config_test.go

@@ -133,22 +133,30 @@ func TestNewConfig(t *testing.T) {
 		name: "with toggles explicitly flipped",
 		input: map[string]string{
 			"enable-scale-to-zero": "false",
+			"min-scale":            "1",
+			"max-scale":            "2",
 		},
 		want: func() *autoscalerconfig.Config {
 			c := defaultConfig()
 			c.EnableScaleToZero = false
+			c.MinScale = 1
+			c.MaxScale = 2
 			return c
 		}(),
 	}, {
 		name: "with explicit grace period",
 		input: map[string]string{
 			"enable-scale-to-zero":       "false",
 			"scale-to-zero-grace-period": "33s",
+			"min-scale":                  "1",
+			"max-scale":                  "2",
 		},
 		want: func() *autoscalerconfig.Config {
 			c := defaultConfig()
 			c.EnableScaleToZero = false
 			c.ScaleToZeroGracePeriod = 33 * time.Second
+			c.MinScale = 1
+			c.MaxScale = 2
 			return c
 		}(),
 	}, {
@@ -350,6 +358,23 @@ func TestNewConfig(t *testing.T) {
 			"max-scale-limit": "11",
 		},
 		wantErr: true,
+	}, {
+		name: "with max scale less than min-scale",
+		input: map[string]string{
+			"min-scale": "4",
+			"max-scale": "3",
+		},
+		wantErr: true,
+	}, {
+		name: "with min scale set but max-scale not set",
+		input: map[string]string{
+			"min-scale": "4",
+		},
+		want: func() *autoscalerconfig.Config {
+			c := defaultConfig()
+			c.MinScale = 4
+			return c
+		}(),
 	}, {
 		name: "with valid default max scale and max scale limit",
 		input: map[string]string{

pkg/reconciler/autoscaling/kpa/kpa_test.go

@@ -111,13 +111,15 @@ func defaultConfigMapData() map[string]string {
 		"panic-window":                            "10s",
 		"scale-to-zero-grace-period":              gracePeriod.String(),
 		"tick-interval":                           "2s",
+		"min-scale":                               "0",
 	}
 }
 
 func initialScaleZeroASConfig() *autoscalerconfig.Config {
 	ac, _ := asconfig.NewConfigFromMap(defaultConfigMapData())
 	ac.AllowZeroInitialScale = true
 	ac.InitialScale = 0
+	ac.MinScale = 0
 	ac.EnableScaleToZero = true
 	return ac
 }