Do not delay min/maxReplicas propagation from HRA to RD due to caching (#406)

As part of #282, I have introduced some caching mechanism to avoid excessive GitHub API calls due to the autoscaling calculation involving GitHub API calls is executed on each Webhook event.

Apparently, it was saving the wrong value in the cache- The value was one after applying `HRA.Spec.{Max,Min}Replicas` so manual changes to {Max,Min}Replicas doesn't affect RunnerDeployment.Spec.Replicas until the cache expires. This isn't what I had wanted.

This patch fixes that, by changing the value being cached to one before applying {Min,Max}Replicas.

Additionally, I've also updated logging so that you observe which number was fetched from cache, and what number was suggested by either TotalNumberOfQueuedAndInProgressWorkflowRuns or PercentageRunnersBusy, and what was the final number used as the desired-replicas(after applying {Min,Max}Replicas).

Follow-up for #282

controllers/autoscaling.go

@@ -34,7 +34,7 @@ func getValueAvailableAt(now time.Time, from, to *time.Time, reservedValue int)
 	return &reservedValue
 }
 
-func (r *HorizontalRunnerAutoscalerReconciler) getDesiredReplicasFromCache(hra v1alpha1.HorizontalRunnerAutoscaler) *int {
+func (r *HorizontalRunnerAutoscalerReconciler) fetchSuggestedReplicasFromCache(hra v1alpha1.HorizontalRunnerAutoscaler) *int {
 	var entry *v1alpha1.CacheEntry
 
 	for i := range hra.Status.CacheEntries {
@@ -63,7 +63,7 @@ func (r *HorizontalRunnerAutoscalerReconciler) getDesiredReplicasFromCache(hra v
 	return nil
 }
 
-func (r *HorizontalRunnerAutoscalerReconciler) determineDesiredReplicas(rd v1alpha1.RunnerDeployment, hra v1alpha1.HorizontalRunnerAutoscaler) (*int, error) {
+func (r *HorizontalRunnerAutoscalerReconciler) suggestDesiredReplicas(rd v1alpha1.RunnerDeployment, hra v1alpha1.HorizontalRunnerAutoscaler) (*int, error) {
 	if hra.Spec.MinReplicas == nil {
 		return nil, fmt.Errorf("horizontalrunnerautoscaler %s/%s is missing minReplicas", hra.Namespace, hra.Name)
 	} else if hra.Spec.MaxReplicas == nil {
@@ -73,20 +73,20 @@ func (r *HorizontalRunnerAutoscalerReconciler) determineDesiredReplicas(rd v1alp
 	metrics := hra.Spec.Metrics
 	if len(metrics) == 0 {
 		if len(hra.Spec.ScaleUpTriggers) == 0 {
-			return r.calculateReplicasByQueuedAndInProgressWorkflowRuns(rd, hra)
+			return r.suggestReplicasByQueuedAndInProgressWorkflowRuns(rd, hra)
 		}
 
-		return hra.Spec.MinReplicas, nil
+		return nil, nil
 	} else if metrics[0].Type == v1alpha1.AutoscalingMetricTypeTotalNumberOfQueuedAndInProgressWorkflowRuns {
-		return r.calculateReplicasByQueuedAndInProgressWorkflowRuns(rd, hra)
+		return r.suggestReplicasByQueuedAndInProgressWorkflowRuns(rd, hra)
 	} else if metrics[0].Type == v1alpha1.AutoscalingMetricTypePercentageRunnersBusy {
-		return r.calculateReplicasByPercentageRunnersBusy(rd, hra)
+		return r.suggestReplicasByPercentageRunnersBusy(rd, hra)
 	} else {
 		return nil, fmt.Errorf("validting autoscaling metrics: unsupported metric type %q", metrics[0].Type)
 	}
 }
 
-func (r *HorizontalRunnerAutoscalerReconciler) calculateReplicasByQueuedAndInProgressWorkflowRuns(rd v1alpha1.RunnerDeployment, hra v1alpha1.HorizontalRunnerAutoscaler) (*int, error) {
+func (r *HorizontalRunnerAutoscalerReconciler) suggestReplicasByQueuedAndInProgressWorkflowRuns(rd v1alpha1.RunnerDeployment, hra v1alpha1.HorizontalRunnerAutoscaler) (*int, error) {
 
 	var repos [][]string
 	metrics := hra.Spec.Metrics
@@ -101,7 +101,7 @@ func (r *HorizontalRunnerAutoscalerReconciler) calculateReplicasByQueuedAndInPro
 		// we assume that the desired replicas should always be `minReplicas + capacityReservedThroughWebhook`.
 		// See https://github.com/summerwind/actions-runner-controller/issues/377#issuecomment-793372693
 		if len(metrics) == 0 {
-			return hra.Spec.MinReplicas, nil
+			return nil, nil
 		}
 
 		if len(metrics[0].RepositoryNames) == 0 {
@@ -178,28 +178,10 @@ func (r *HorizontalRunnerAutoscalerReconciler) calculateReplicasByQueuedAndInPro
 		}
 	}
 
-	minReplicas := *hra.Spec.MinReplicas
-	maxReplicas := *hra.Spec.MaxReplicas
 	necessaryReplicas := queued + inProgress
 
-	var desiredReplicas int
-
-	if necessaryReplicas < minReplicas {
-		desiredReplicas = minReplicas
-	} else if necessaryReplicas > maxReplicas {
-		desiredReplicas = maxReplicas
-	} else {
-		desiredReplicas = necessaryReplicas
-	}
-
-	rd.Status.Replicas = &desiredReplicas
-	replicas := desiredReplicas
-
 	r.Log.V(1).Info(
-		"Calculated desired replicas",
+		fmt.Sprintf("Suggested desired replicas of %d by TotalNumberOfQueuedAndInProgressWorkflowRuns", necessaryReplicas),
-		"computed_replicas_desired", desiredReplicas,
-		"spec_replicas_min", minReplicas,
-		"spec_replicas_max", maxReplicas,
 		"workflow_runs_completed", completed,
 		"workflow_runs_in_progress", inProgress,
 		"workflow_runs_queued", queued,
@@ -209,13 +191,11 @@ func (r *HorizontalRunnerAutoscalerReconciler) calculateReplicasByQueuedAndInPro
 		"horizontal_runner_autoscaler", hra.Name,
 	)
 
-	return &replicas, nil
+	return &necessaryReplicas, nil
 }
 
-func (r *HorizontalRunnerAutoscalerReconciler) calculateReplicasByPercentageRunnersBusy(rd v1alpha1.RunnerDeployment, hra v1alpha1.HorizontalRunnerAutoscaler) (*int, error) {
+func (r *HorizontalRunnerAutoscalerReconciler) suggestReplicasByPercentageRunnersBusy(rd v1alpha1.RunnerDeployment, hra v1alpha1.HorizontalRunnerAutoscaler) (*int, error) {
 	ctx := context.Background()
-	minReplicas := *hra.Spec.MinReplicas
-	maxReplicas := *hra.Spec.MaxReplicas
 	metrics := hra.Spec.Metrics[0]
 	scaleUpThreshold := defaultScaleUpThreshold
 	scaleDownThreshold := defaultScaleDownThreshold
@@ -363,21 +343,13 @@ func (r *HorizontalRunnerAutoscalerReconciler) calculateReplicasByPercentageRunn
 		desiredReplicas = *rd.Spec.Replicas
 	}
 
-	if desiredReplicas < minReplicas {
-		desiredReplicas = minReplicas
-	} else if desiredReplicas > maxReplicas {
-		desiredReplicas = maxReplicas
-	}
-
 	// NOTES for operators:
 	//
 	// - num_runners can be as twice as large as replicas_desired_before while
 	//   the runnerdeployment controller is replacing RunnerReplicaSet for runner update.
 
 	r.Log.V(1).Info(
-		"Calculated desired replicas",
+		fmt.Sprintf("Suggested desired replicas of %d by PercentageRunnersBusy", desiredReplicas),
-		"replicas_min", minReplicas,
-		"replicas_max", maxReplicas,
 		"replicas_desired_before", desiredReplicasBefore,
 		"replicas_desired", desiredReplicas,
 		"num_runners", numRunners,
@@ -391,8 +363,5 @@ func (r *HorizontalRunnerAutoscalerReconciler) calculateReplicasByPercentageRunn
 		"repository", repository,
 	)
 
-	rd.Status.Replicas = &desiredReplicas
+	return &desiredReplicas, nil
-	replicas := desiredReplicas
-
-	return &replicas, nil
 }

controllers/autoscaling_test.go

@@ -224,7 +224,7 @@ func TestDetermineDesiredReplicas_RepositoryRunner(t *testing.T) {
 				},
 			}
 
-			got, err := h.computeReplicas(rd, hra)
+			got, _, _, err := h.computeReplicasWithCache(log, metav1Now.Time, rd, hra)
 			if err != nil {
 				if tc.err == "" {
 					t.Fatalf("unexpected error: expected none, got %v", err)
@@ -234,12 +234,8 @@ func TestDetermineDesiredReplicas_RepositoryRunner(t *testing.T) {
 				return
 			}
 
-			if got == nil {
+			if got != tc.want {
-				t.Fatalf("unexpected value of rs.Spec.Replicas: nil")
+				t.Errorf("%d: incorrect desired replicas: want %d, got %d", i, tc.want, got)
-			}
-
-			if *got != tc.want {
-				t.Errorf("%d: incorrect desired replicas: want %d, got %d", i, tc.want, *got)
 			}
 		})
 	}
@@ -424,6 +420,8 @@ func TestDetermineDesiredReplicas_OrganizationalRunner(t *testing.T) {
 		_ = v1alpha1.AddToScheme(scheme)
 
 		t.Run(fmt.Sprintf("case %d", i), func(t *testing.T) {
+			t.Helper()
+
 			server := fake.NewServer(
 				fake.WithListRepositoryWorkflowRunsResponse(200, tc.workflowRuns, tc.workflowRuns_queued, tc.workflowRuns_in_progress),
 				fake.WithListWorkflowJobsResponse(200, tc.workflowJobs),
@@ -485,7 +483,7 @@ func TestDetermineDesiredReplicas_OrganizationalRunner(t *testing.T) {
 				},
 			}
 
-			got, err := h.computeReplicas(rd, hra)
+			got, _, _, err := h.computeReplicasWithCache(log, metav1Now.Time, rd, hra)
 			if err != nil {
 				if tc.err == "" {
 					t.Fatalf("unexpected error: expected none, got %v", err)
@@ -495,12 +493,8 @@ func TestDetermineDesiredReplicas_OrganizationalRunner(t *testing.T) {
 				return
 			}
 
-			if got == nil {
+			if got != tc.want {
-				t.Fatalf("unexpected value of rs.Spec.Replicas: nil, wanted %v", tc.want)
+				t.Errorf("%d: incorrect desired replicas: want %d, got %d", i, tc.want, got)
-			}
-
-			if *got != tc.want {
-				t.Errorf("%d: incorrect desired replicas: want %d, got %d", i, tc.want, *got)
 			}
 		})
 	}

controllers/horizontalrunnerautoscaler_controller.go

@@ -19,6 +19,7 @@ package controllers
 import (
 	"context"
 	"fmt"
+	corev1 "k8s.io/api/core/v1"
 	"time"
 
 	"github.com/summerwind/actions-runner-controller/github"
@@ -30,7 +31,6 @@ import (
 	ctrl "sigs.k8s.io/controller-runtime"
 	"sigs.k8s.io/controller-runtime/pkg/client"
 
-	corev1 "k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 
 	"github.com/summerwind/actions-runner-controller/api/v1alpha1"
@@ -52,6 +52,8 @@ type HorizontalRunnerAutoscalerReconciler struct {
 	Name          string
 }
 
+const defaultReplicas = 1
+
 // +kubebuilder:rbac:groups=actions.summerwind.dev,resources=runnerdeployments,verbs=get;list;watch;update;patch
 // +kubebuilder:rbac:groups=actions.summerwind.dev,resources=horizontalrunnerautoscalers,verbs=get;list;watch;create;update;patch;delete
 // +kubebuilder:rbac:groups=actions.summerwind.dev,resources=horizontalrunnerautoscalers/finalizers,verbs=get;list;watch;create;update;patch;delete
@@ -83,41 +85,18 @@ func (r *HorizontalRunnerAutoscalerReconciler) Reconcile(req ctrl.Request) (ctrl
 		return ctrl.Result{}, nil
 	}
 
-	var replicas *int
-
-	replicasFromCache := r.getDesiredReplicasFromCache(hra)
-
-	if replicasFromCache != nil {
-		replicas = replicasFromCache
-	} else {
-		var err error
-
-		replicas, err = r.computeReplicas(rd, hra)
-		if err != nil {
-			r.Recorder.Event(&hra, corev1.EventTypeNormal, "RunnerAutoscalingFailure", err.Error())
-
-			log.Error(err, "Could not compute replicas")
-
-			return ctrl.Result{}, err
-		}
-	}
-
-	const defaultReplicas = 1
-
-	currentDesiredReplicas := getIntOrDefault(rd.Spec.Replicas, defaultReplicas)
-	newDesiredReplicas := getIntOrDefault(replicas, defaultReplicas)
-
 	now := time.Now()
 
-	for _, reservation := range hra.Spec.CapacityReservations {
+	newDesiredReplicas, computedReplicas, computedReplicasFromCache, err := r.computeReplicasWithCache(log, now, rd, hra)
-		if reservation.ExpirationTime.Time.After(now) {
+	if err != nil {
-			newDesiredReplicas += reservation.Replicas
+		r.Recorder.Event(&hra, corev1.EventTypeNormal, "RunnerAutoscalingFailure", err.Error())
-		}
+
+		log.Error(err, "Could not compute replicas")
+
+		return ctrl.Result{}, err
 	}
 
-	if hra.Spec.MaxReplicas != nil && *hra.Spec.MaxReplicas < newDesiredReplicas {
+	currentDesiredReplicas := getIntOrDefault(rd.Spec.Replicas, defaultReplicas)
-		newDesiredReplicas = *hra.Spec.MaxReplicas
-	}
 
 	// Please add more conditions that we can in-place update the newest runnerreplicaset without disruption
 	if currentDesiredReplicas != newDesiredReplicas {
@@ -143,7 +122,7 @@ func (r *HorizontalRunnerAutoscalerReconciler) Reconcile(req ctrl.Request) (ctrl
 		updated.Status.DesiredReplicas = &newDesiredReplicas
 	}
 
-	if replicasFromCache == nil {
+	if computedReplicasFromCache == nil {
 		if updated == nil {
 			updated = hra.DeepCopy()
 		}
@@ -160,7 +139,7 @@ func (r *HorizontalRunnerAutoscalerReconciler) Reconcile(req ctrl.Request) (ctrl
 
 		updated.Status.CacheEntries = append(cacheEntries, v1alpha1.CacheEntry{
 			Key:            v1alpha1.CacheEntryKeyDesiredReplicas,
-			Value:          *replicas,
+			Value:          computedReplicas,
 			ExpirationTime: metav1.Time{Time: time.Now().Add(cacheDuration)},
 		})
 	}
@@ -200,14 +179,59 @@ func (r *HorizontalRunnerAutoscalerReconciler) SetupWithManager(mgr ctrl.Manager
 		Complete(r)
 }
 
-func (r *HorizontalRunnerAutoscalerReconciler) computeReplicas(rd v1alpha1.RunnerDeployment, hra v1alpha1.HorizontalRunnerAutoscaler) (*int, error) {
+func (r *HorizontalRunnerAutoscalerReconciler) computeReplicasWithCache(log logr.Logger, now time.Time, rd v1alpha1.RunnerDeployment, hra v1alpha1.HorizontalRunnerAutoscaler) (int, int, *int, error) {
-	var computedReplicas *int
+	minReplicas := defaultReplicas
-
+	if hra.Spec.MinReplicas != nil && *hra.Spec.MinReplicas > 0 {
-	replicas, err := r.determineDesiredReplicas(rd, hra)
+		minReplicas = *hra.Spec.MinReplicas
-	if err != nil {
-		return nil, err
 	}
 
+	var suggestedReplicas int
+
+	suggestedReplicasFromCache := r.fetchSuggestedReplicasFromCache(hra)
+
+	var cached *int
+
+	if suggestedReplicasFromCache != nil {
+		cached = suggestedReplicasFromCache
+
+		if cached == nil {
+			suggestedReplicas = minReplicas
+		} else {
+			suggestedReplicas = *cached
+		}
+	} else {
+		v, err := r.suggestDesiredReplicas(rd, hra)
+		if err != nil {
+			return 0, 0, nil, err
+		}
+
+		if v == nil {
+			suggestedReplicas = minReplicas
+		} else {
+			suggestedReplicas = *v
+		}
+	}
+
+	var reserved int
+
+	for _, reservation := range hra.Spec.CapacityReservations {
+		if reservation.ExpirationTime.Time.After(now) {
+			reserved += reservation.Replicas
+		}
+	}
+
+	newDesiredReplicas := suggestedReplicas + reserved
+
+	if newDesiredReplicas < minReplicas {
+		newDesiredReplicas = minReplicas
+	} else if hra.Spec.MaxReplicas != nil && newDesiredReplicas > *hra.Spec.MaxReplicas {
+		newDesiredReplicas = *hra.Spec.MaxReplicas
+	}
+
+	//
+	// Delay scaling-down for ScaleDownDelaySecondsAfterScaleUp or DefaultScaleDownDelay
+	//
+
 	var scaleDownDelay time.Duration
 
 	if hra.Spec.ScaleDownDelaySecondsAfterScaleUp != nil {
@@ -216,17 +240,50 @@ func (r *HorizontalRunnerAutoscalerReconciler) computeReplicas(rd v1alpha1.Runne
 		scaleDownDelay = DefaultScaleDownDelay
 	}
 
-	now := time.Now()
+	var scaleDownDelayUntil *time.Time
 
 	if hra.Status.DesiredReplicas == nil ||
-		*hra.Status.DesiredReplicas < *replicas ||
+		*hra.Status.DesiredReplicas < newDesiredReplicas ||
-		hra.Status.LastSuccessfulScaleOutTime == nil ||
+		hra.Status.LastSuccessfulScaleOutTime == nil {
-		hra.Status.LastSuccessfulScaleOutTime.Add(scaleDownDelay).Before(now) {
 
-		computedReplicas = replicas
+	} else if hra.Status.LastSuccessfulScaleOutTime != nil {
+		t := hra.Status.LastSuccessfulScaleOutTime.Add(scaleDownDelay)
+
+		// ScaleDownDelay is not passed
+		if t.After(now) {
+			scaleDownDelayUntil = &t
+			newDesiredReplicas = *hra.Status.DesiredReplicas
+		}
 	} else {
-		computedReplicas = hra.Status.DesiredReplicas
+		newDesiredReplicas = *hra.Status.DesiredReplicas
 	}
 
-	return computedReplicas, nil
+	//
+	// Logs various numbers for monitoring and debugging purpose
+	//
+
+	kvs := []interface{}{
+		"suggested", suggestedReplicas,
+		"reserved", reserved,
+		"min", minReplicas,
+	}
+
+	if cached != nil {
+		kvs = append(kvs, "cached", *cached)
+	}
+
+	if scaleDownDelayUntil != nil {
+		kvs = append(kvs, "last_scale_up_time", *hra.Status.LastSuccessfulScaleOutTime)
+		kvs = append(kvs, "scale_down_delay_until", scaleDownDelayUntil)
+	}
+
+	if maxReplicas := hra.Spec.MaxReplicas; maxReplicas != nil {
+		kvs = append(kvs, "max", *maxReplicas)
+	}
+
+	log.V(1).Info(fmt.Sprintf("Calculated desired replicas of %d", newDesiredReplicas),
+		kvs...,
+	)
+
+	return newDesiredReplicas, suggestedReplicas, suggestedReplicasFromCache, nil
 }