If we set SelectPolicy MinPolicySelect on scaleUp behavior or scaleDown behavior,Horizontal Pod Autoscaler doesn`t automatically scale the number of pods correctly

Signed-off-by: weiwei <[email protected]>

Author: weiwei

pkg/controller/podautoscaler/horizontal.go

@@ -998,15 +998,17 @@ func calculateScaleUpLimitWithScalingRules(currentReplicas int32, scaleEvents []
 	if *scalingRules.SelectPolicy == autoscalingv2.DisabledPolicySelect {
 		return currentReplicas // Scaling is disabled
 	} else if *scalingRules.SelectPolicy == autoscalingv2.MinPolicySelect {
+		result = math.MaxInt32
 		selectPolicyFn = min // For scaling up, the lowest change ('min' policy) produces a minimum value
 	} else {
+		result = math.MinInt32
 		selectPolicyFn = max // Use the default policy otherwise to produce a highest possible change
 	}
 	for _, policy := range scalingRules.Policies {
 		replicasAddedInCurrentPeriod := getReplicasChangePerPeriod(policy.PeriodSeconds, scaleEvents)
 		periodStartReplicas := currentReplicas - replicasAddedInCurrentPeriod
 		if policy.Type == autoscalingv2.PodsScalingPolicy {
-			proposed = int32(periodStartReplicas + policy.Value)
+			proposed = periodStartReplicas + policy.Value
 		} else if policy.Type == autoscalingv2.PercentScalingPolicy {
 			// the proposal has to be rounded up because the proposed change might not increase the replica count causing the target to never scale up
 			proposed = int32(math.Ceil(float64(periodStartReplicas) * (1 + float64(policy.Value)/100)))
@@ -1018,14 +1020,16 @@ func calculateScaleUpLimitWithScalingRules(currentReplicas int32, scaleEvents []
 
 // calculateScaleDownLimitWithBehavior returns the maximum number of pods that could be deleted for the given HPAScalingRules
 func calculateScaleDownLimitWithBehaviors(currentReplicas int32, scaleEvents []timestampedScaleEvent, scalingRules *autoscalingv2.HPAScalingRules) int32 {
-	var result int32 = math.MaxInt32
+	var result int32
 	var proposed int32
 	var selectPolicyFn func(int32, int32) int32
 	if *scalingRules.SelectPolicy == autoscalingv2.DisabledPolicySelect {
 		return currentReplicas // Scaling is disabled
 	} else if *scalingRules.SelectPolicy == autoscalingv2.MinPolicySelect {
+		result = math.MinInt32
 		selectPolicyFn = max // For scaling down, the lowest change ('min' policy) produces a maximum value
 	} else {
+		result = math.MaxInt32
 		selectPolicyFn = min // Use the default policy otherwise to produce a highest possible change
 	}
 	for _, policy := range scalingRules.Policies {

pkg/controller/podautoscaler/horizontal_test.go

@@ -2993,6 +2993,50 @@ func TestConvertDesiredReplicasWithRules(t *testing.T) {
 	}
 }
 
+func TestCalculateScaleUpLimitWithScalingRules(t *testing.T) {
+	policy := autoscalingv2.MinPolicySelect
+
+	calculated := calculateScaleUpLimitWithScalingRules(1, []timestampedScaleEvent{}, &autoscalingv2.HPAScalingRules{
+		StabilizationWindowSeconds: utilpointer.Int32Ptr(300),
+		SelectPolicy:               &policy,
+		Policies: []autoscalingv2.HPAScalingPolicy{
+			{
+				Type:          autoscalingv2.PodsScalingPolicy,
+				Value:         2,
+				PeriodSeconds: 60,
+			},
+			{
+				Type:          autoscalingv2.PercentScalingPolicy,
+				Value:         50,
+				PeriodSeconds: 60,
+			},
+		},
+	})
+	assert.Equal(t, calculated, int32(2))
+}
+
+func TestCalculateScaleDownLimitWithBehaviors(t *testing.T) {
+	policy := autoscalingv2.MinPolicySelect
+
+	calculated := calculateScaleDownLimitWithBehaviors(5, []timestampedScaleEvent{}, &autoscalingv2.HPAScalingRules{
+		StabilizationWindowSeconds: utilpointer.Int32Ptr(300),
+		SelectPolicy:               &policy,
+		Policies: []autoscalingv2.HPAScalingPolicy{
+			{
+				Type:          autoscalingv2.PodsScalingPolicy,
+				Value:         2,
+				PeriodSeconds: 60,
+			},
+			{
+				Type:          autoscalingv2.PercentScalingPolicy,
+				Value:         50,
+				PeriodSeconds: 60,
+			},
+		},
+	})
+	assert.Equal(t, calculated, int32(3))
+}
+
 func generateScalingRules(pods, podsPeriod, percent, percentPeriod, stabilizationWindow int32) *autoscalingv2.HPAScalingRules {
 	policy := autoscalingv2.MaxPolicySelect
 	directionBehavior := autoscalingv2.HPAScalingRules{