`scale{Up,Down}Adjustment` to add/remove constant number of replicas on scaling (#315)

* `scale{Up,Down}Adjustment` to add/remove constant number of replicas on scaling

Ref #305

* Bump chart version

api/v1alpha1/horizontalrunnerautoscaler_types.go

@@ -126,6 +126,16 @@ type MetricSpec struct {
 	// to determine how many pods should be removed.
 	// +optional
 	ScaleDownFactor string `json:"scaleDownFactor,omitempty"`
+
+	// ScaleUpAdjustment is the number of runners added on scale-up.
+	// You can only specify either ScaleUpFactor or ScaleUpAdjustment.
+	// +optional
+	ScaleUpAdjustment int `json:"scaleUpAdjustment,omitempty"`
+
+	// ScaleDownAdjustment is the number of runners removed on scale-down.
+	// You can only specify either ScaleDownFactor or ScaleDownAdjustment.
+	// +optional
+	ScaleDownAdjustment int `json:"scaleDownAdjustment,omitempty"`
 }
 
 type HorizontalRunnerAutoscalerStatus struct {

charts/actions-runner-controller/Chart.yaml

@@ -15,7 +15,7 @@ type: application
 # This is the chart version. This version number should be incremented each time you make changes
 # to the chart and its templates, including the app version.
 # Versions are expected to follow Semantic Versioning (https://semver.org/)
-version: 0.4.0
+version: 0.5.0
 
 home: https://github.com/summerwind/actions-runner-controller
 

charts/actions-runner-controller/crds/actions.summerwind.dev_horizontalrunnerautoscalers.yaml

@@ -78,6 +78,11 @@ spec:
                     items:
                       type: string
                     type: array
+                  scaleDownAdjustment:
+                    description: ScaleDownAdjustment is the number of runners removed
+                      on scale-down. You can only specify either ScaleDownFactor or
+                      ScaleDownAdjustment.
+                    type: integer
                   scaleDownFactor:
                     description: ScaleDownFactor is the multiplicative factor applied
                       to the current number of runners used to determine how many
@@ -87,6 +92,10 @@ spec:
                     description: ScaleDownThreshold is the percentage of busy runners
                       less than which will trigger the hpa to scale the runners down.
                     type: string
+                  scaleUpAdjustment:
+                    description: ScaleUpAdjustment is the number of runners added
+                      on scale-up. You can only specify either ScaleUpFactor or ScaleUpAdjustment.
+                    type: integer
                   scaleUpFactor:
                     description: ScaleUpFactor is the multiplicative factor applied
                       to the current number of runners used to determine how many

config/crd/bases/actions.summerwind.dev_horizontalrunnerautoscalers.yaml

@@ -78,6 +78,11 @@ spec:
                     items:
                       type: string
                     type: array
+                  scaleDownAdjustment:
+                    description: ScaleDownAdjustment is the number of runners removed
+                      on scale-down. You can only specify either ScaleDownFactor or
+                      ScaleDownAdjustment.
+                    type: integer
                   scaleDownFactor:
                     description: ScaleDownFactor is the multiplicative factor applied
                       to the current number of runners used to determine how many
@@ -87,6 +92,10 @@ spec:
                     description: ScaleDownThreshold is the percentage of busy runners
                       less than which will trigger the hpa to scale the runners down.
                     type: string
+                  scaleUpAdjustment:
+                    description: ScaleUpAdjustment is the number of runners added
+                      on scale-up. You can only specify either ScaleUpFactor or ScaleUpAdjustment.
+                    type: integer
                   scaleUpFactor:
                     description: ScaleUpFactor is the multiplicative factor applied
                       to the current number of runners used to determine how many

controllers/autoscaling.go

@@ -222,14 +222,34 @@ func (r *HorizontalRunnerAutoscalerReconciler) calculateReplicasByPercentageRunn
 
 		scaleDownThreshold = sdt
 	}
+
+	scaleUpAdjustment := metrics.ScaleUpAdjustment
+	if scaleUpAdjustment != 0 {
+		if metrics.ScaleUpAdjustment < 0 {
+			return nil, errors.New("validating autoscaling metrics: spec.autoscaling.metrics[].scaleUpAdjustment cannot be lower than 0")
+		}
+
 		if metrics.ScaleUpFactor != "" {
+			return nil, errors.New("validating autoscaling metrics: spec.autoscaling.metrics[]: scaleUpAdjustment and scaleUpFactor cannot be specified together")
+		}
+	} else if metrics.ScaleUpFactor != "" {
 		suf, err := strconv.ParseFloat(metrics.ScaleUpFactor, 64)
 		if err != nil {
 			return nil, errors.New("validating autoscaling metrics: spec.autoscaling.metrics[].scaleUpFactor cannot be parsed into a float64")
 		}
 		scaleUpFactor = suf
 	}
+
+	scaleDownAdjustment := metrics.ScaleDownAdjustment
+	if scaleDownAdjustment != 0 {
+		if metrics.ScaleDownAdjustment < 0 {
+			return nil, errors.New("validating autoscaling metrics: spec.autoscaling.metrics[].scaleDownAdjustment cannot be lower than 0")
+		}
+
 		if metrics.ScaleDownFactor != "" {
+			return nil, errors.New("validating autoscaling metrics: spec.autoscaling.metrics[]: scaleDownAdjustment and scaleDownFactor cannot be specified together")
+		}
+	} else if metrics.ScaleDownFactor != "" {
 		sdf, err := strconv.ParseFloat(metrics.ScaleDownFactor, 64)
 		if err != nil {
 			return nil, errors.New("validating autoscaling metrics: spec.autoscaling.metrics[].scaleDownFactor cannot be parsed into a float64")
@@ -273,9 +293,17 @@ func (r *HorizontalRunnerAutoscalerReconciler) calculateReplicasByPercentageRunn
 	var desiredReplicas int
 	fractionBusy := float64(numRunnersBusy) / float64(numRunners)
 	if fractionBusy >= scaleUpThreshold {
+		if scaleUpAdjustment > 0 {
+			desiredReplicas = numRunners + scaleUpAdjustment
+		} else {
 			desiredReplicas = int(math.Ceil(float64(numRunners) * scaleUpFactor))
+		}
 	} else if fractionBusy < scaleDownThreshold {
+		if scaleDownAdjustment > 0 {
+			desiredReplicas = numRunners - scaleDownAdjustment
+		} else {
 			desiredReplicas = int(float64(numRunners) * scaleDownFactor)
+		}
 	} else {
 		desiredReplicas = *rd.Spec.Replicas
 	}