Defer scale up until the listener publishes a state that accounts for finished runners

Spec.Replicas is the count the listener asked for when it published
Spec.PatchID. When the EphemeralRunnerSet controller cleaned up finished
runners in the same reconcile, it then compared that count against a live
count the cleanup had just reduced, and created runners to replace jobs
that had already completed. Nobody asked for those runners.

Delete the finished runners, record the patch ID the cleanup belongs to in
Status.FinishedRunnerCleanupPatchID, and return, so the scaling decision is
made on the next reconcile against post-cleanup data. Scale up stays
suppressed while Spec.PatchID still equals that recorded patch ID: the gap
below Spec.Replicas is the one the cleanup opened, not new demand. The
listener marks itself dirty on every job completion and publishes a fresh
incrementing patch ID, so the suppression lifts as soon as it reports a
desired state that accounts for the completions.

Runners that are mid-deletion were not counted at all, which let the
controller over-create while deletions were still in flight. Count them
towards the scale-up total.

The cleanup helper is renamed to deleteTerminatedEphemeralRunners because
it is no longer specific to finished runners.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

apis/actions.github.com/v1alpha1/ephemeralrunnerset_types.go

@@ -53,6 +53,12 @@ type EphemeralRunnerSetStatus struct {
 	// Unset defaults to 0.
 	// +optional
 	AppliedActionableRevision int64 `json:"appliedActionableRevision,omitempty"`
+	// FinishedRunnerCleanupPatchID records the listener patch ID for which finished
+	// ephemeral runners were cleaned up. Scale-up is suppressed for the same patch ID
+	// until the listener publishes a fresh desired-state patch.
+	// Unset defaults to 0.
+	// +optional
+	FinishedRunnerCleanupPatchID int `json:"finishedRunnerCleanupPatchID,omitempty"`
 }
 
 // EphemeralRunnerSetPhase is the phase of the ephemeral runner set resource

charts/gha-runner-scale-set-controller-experimental/crds/actions.github.com_ephemeralrunnersets.yaml

@@ -8310,6 +8310,13 @@ spec:
                     Unset defaults to 0.
                   format: int64
                   type: integer
+                finishedRunnerCleanupPatchID:
+                  description: |-
+                    FinishedRunnerCleanupPatchID records the listener patch ID for which finished
+                    ephemeral runners were cleaned up. Scale-up is suppressed for the same patch ID
+                    until the listener publishes a fresh desired-state patch.
+                    Unset defaults to 0.
+                  type: integer
                 phase:
                   description: EphemeralRunnerSetPhase is the phase of the ephemeral runner set resource
                   type: string

charts/gha-runner-scale-set-controller/crds/actions.github.com_ephemeralrunnersets.yaml

@@ -8310,6 +8310,13 @@ spec:
                     Unset defaults to 0.
                   format: int64
                   type: integer
+                finishedRunnerCleanupPatchID:
+                  description: |-
+                    FinishedRunnerCleanupPatchID records the listener patch ID for which finished
+                    ephemeral runners were cleaned up. Scale-up is suppressed for the same patch ID
+                    until the listener publishes a fresh desired-state patch.
+                    Unset defaults to 0.
+                  type: integer
                 phase:
                   description: EphemeralRunnerSetPhase is the phase of the ephemeral runner set resource
                   type: string

config/crd/bases/actions.github.com_ephemeralrunnersets.yaml

@@ -8310,6 +8310,13 @@ spec:
                     Unset defaults to 0.
                   format: int64
                   type: integer
+                finishedRunnerCleanupPatchID:
+                  description: |-
+                    FinishedRunnerCleanupPatchID records the listener patch ID for which finished
+                    ephemeral runners were cleaned up. Scale-up is suppressed for the same patch ID
+                    until the listener publishes a fresh desired-state patch.
+                    Unset defaults to 0.
+                  type: integer
                 phase:
                   description: EphemeralRunnerSetPhase is the phase of the ephemeral runner set resource
                   type: string

controllers/actions.github.com/ephemeralrunnerset_controller.go

@@ -204,15 +204,43 @@ func (r *EphemeralRunnerSetReconciler) Reconcile(ctx context.Context, req ctrl.R
 
 	total := ephemeralRunnersByState.scaleTotal()
 	if ephemeralRunnerSet.Spec.PatchID == 0 || ephemeralRunnerSet.Spec.PatchID != ephemeralRunnersByState.latestPatchID {
-		defer func() {
-			if err := r.cleanupFinishedEphemeralRunners(ctx, ephemeralRunnersByState.finished, log); err != nil {
+		// Spec.Replicas is the count the listener asked for when it published
+		// Spec.PatchID. Deleting finished runners here changes the live count that
+		// the count was computed against, so satisfying it in the same pass would
+		// create runners to replace jobs that have already completed. Record the
+		// patch ID the cleanup belongs to and return, leaving the scaling decision
+		// to the next reconcile, which sees the post-cleanup state.
+		if len(ephemeralRunnersByState.finished) > 0 {
+			if err := r.deleteTerminatedEphemeralRunners(ctx, ephemeralRunnersByState.finished, log); err != nil {
 				log.Error(err, "failed to cleanup finished ephemeral runners")
+				return ctrl.Result{}, err
 			}
-		}()
-		log.Info("Scaling comparison", "current", total, "desired", ephemeralRunnerSet.Spec.Replicas)
+			if err := r.patchFinishedRunnerCleanupPatchIDStatus(ctx, req.NamespacedName, ephemeralRunnerSet.Spec.PatchID); err != nil {
+				log.Error(err, "failed to update finished runner cleanup patch ID status")
+				return ctrl.Result{}, err
+			}
+			ephemeralRunnerSet.Status.FinishedRunnerCleanupPatchID = ephemeralRunnerSet.Spec.PatchID
+
+			log.Info("Finished ephemeral runners were cleaned up, deferring scaling decision")
+			return ctrl.Result{}, r.updateStatus(ctx, &ephemeralRunnerSet, ephemeralRunnersByState, log)
+		}
+
+		// Runners that are being deleted still exist and still hold their
+		// registration, so counting only the live ones would let the controller
+		// create replacements for runners that have not gone away yet.
+		scaleUpTotal := total + len(ephemeralRunnersByState.deleting)
+		log.Info("Scaling comparison", "current", total, "deleting", len(ephemeralRunnersByState.deleting), "desired", ephemeralRunnerSet.Spec.Replicas)
 		switch {
-		case total < ephemeralRunnerSet.Spec.Replicas: // Handle scale up
-			count := ephemeralRunnerSet.Spec.Replicas - total
+		case scaleUpTotal < ephemeralRunnerSet.Spec.Replicas: // Handle scale up
+			// The gap below Spec.Replicas is the one the cleanup above opened for
+			// this patch ID, not new demand. Wait for the listener to publish a
+			// fresh desired state before acting on it.
+			if ephemeralRunnerSet.Spec.PatchID > 0 && ephemeralRunnerSet.Status.FinishedRunnerCleanupPatchID == ephemeralRunnerSet.Spec.PatchID {
+				log.Info("Skipping scale up until listener publishes a fresh desired state after finished runner cleanup", "patchID", ephemeralRunnerSet.Spec.PatchID)
+				return ctrl.Result{}, r.updateStatus(ctx, &ephemeralRunnerSet, ephemeralRunnersByState, log)
+			}
+
+			count := ephemeralRunnerSet.Spec.Replicas - scaleUpTotal
 			log.Info("Creating new ephemeral runners (scale up)", "count", count)
 			if err := r.createEphemeralRunners(ctx, &ephemeralRunnerSet, count, log); err != nil {
 				log.Error(err, "failed to make ephemeral runner")
@@ -277,6 +305,31 @@ func (r *EphemeralRunnerSetReconciler) patchAppliedActionableRevisionStatus(ctx
 	})
 }
 
+// patchFinishedRunnerCleanupPatchIDStatus records that finished runners were
+// deleted while serving patchID, so a later reconcile can tell the resulting gap
+// below Spec.Replicas apart from genuine new demand.
+//
+// Like the applied revision above, this is written after the deletions succeed
+// and re-fetches the object inside the retry, so a conflicting write is never
+// resolved by replaying a status that predates the cleanup.
+func (r *EphemeralRunnerSetReconciler) patchFinishedRunnerCleanupPatchIDStatus(ctx context.Context, key types.NamespacedName, patchID int) error {
+	return retry.RetryOnConflict(retry.DefaultBackoff, func() error {
+		var latest v1alpha1.EphemeralRunnerSet
+		if err := r.Get(ctx, key, &latest); err != nil {
+			return err
+		}
+
+		if latest.Status.FinishedRunnerCleanupPatchID == patchID {
+			return nil
+		}
+
+		original := latest.DeepCopy()
+		latest.Status.FinishedRunnerCleanupPatchID = patchID
+
+		return r.Status().Patch(ctx, &latest, client.MergeFrom(original))
+	})
+}
+
 func (r *EphemeralRunnerSetReconciler) updateStatus(ctx context.Context, ephemeralRunnerSet *v1alpha1.EphemeralRunnerSet, state *ephemeralRunnersByState, log logr.Logger) error {
 	original := ephemeralRunnerSet.DeepCopy()
 	var phase v1alpha1.EphemeralRunnerSetPhase
@@ -289,8 +342,9 @@ func (r *EphemeralRunnerSetReconciler) updateStatus(ctx context.Context, ephemer
 		phase = ephemeralRunnerSet.Status.Phase
 	}
 	desiredStatus := v1alpha1.EphemeralRunnerSetStatus{
-		Phase:                     phase,
-		AppliedActionableRevision: ephemeralRunnerSet.Status.AppliedActionableRevision,
+		Phase:                        phase,
+		AppliedActionableRevision:    ephemeralRunnerSet.Status.AppliedActionableRevision,
+		FinishedRunnerCleanupPatchID: ephemeralRunnerSet.Status.FinishedRunnerCleanupPatchID,
 	}
 
 	// Update the status if needed.
@@ -306,12 +360,13 @@ func (r *EphemeralRunnerSetReconciler) updateStatus(ctx context.Context, ephemer
 	return nil
 }
 
-func (r *EphemeralRunnerSetReconciler) cleanupFinishedEphemeralRunners(ctx context.Context, finishedEphemeralRunners []*v1alpha1.EphemeralRunner, log logr.Logger) error {
-	// cleanup finished runners and proceed
+// deleteTerminatedEphemeralRunners deletes runners that have reached a terminal
+// state and are no longer useful, so that the scaling logic can replace them.
+func (r *EphemeralRunnerSetReconciler) deleteTerminatedEphemeralRunners(ctx context.Context, ephemeralRunners []*v1alpha1.EphemeralRunner, log logr.Logger) error {
 	var errs []error
-	for i := range finishedEphemeralRunners {
-		log.Info("Deleting finished ephemeral runner", "name", finishedEphemeralRunners[i].Name)
-		if err := r.Delete(ctx, finishedEphemeralRunners[i]); err != nil {
+	for i := range ephemeralRunners {
+		log.Info("Deleting terminated ephemeral runner", "name", ephemeralRunners[i].Name, "phase", ephemeralRunners[i].Status.Phase)
+		if err := r.Delete(ctx, ephemeralRunners[i]); err != nil {
 			if !kerrors.IsNotFound(err) {
 				errs = append(errs, err)
 			}

controllers/actions.github.com/ephemeralrunnerset_controller_test.go

@@ -627,7 +627,7 @@ var _ = Describe("Test EphemeralRunnerSet controller", func() {
 
 			// confirm they are not deleted
 			runnerList = new(v1alpha1.EphemeralRunnerList)
-			Consistently(
+			Eventually(
 				func() (int, error) {
 					err := listEphemeralRunnersAndRemoveFinalizers(ctx, k8sClient, runnerList, ephemeralRunnerSet.Namespace)
 					if err != nil {
@@ -690,7 +690,32 @@ var _ = Describe("Test EphemeralRunnerSet controller", func() {
 			Expect(err).NotTo(HaveOccurred(), "failed to update EphemeralRunnerSet")
 
 			runnerList = new(v1alpha1.EphemeralRunnerList)
-			// We should have 3 runners, and have no Succeeded ones
+			Eventually(
+				func() (int, error) {
+					err := listEphemeralRunnersAndRemoveFinalizers(ctx, k8sClient, runnerList, ephemeralRunnerSet.Namespace)
+					if err != nil {
+						return -1, err
+					}
+
+					return len(runnerList.Items), nil
+				},
+				ephemeralRunnerSetTestTimeout,
+				ephemeralRunnerSetTestInterval,
+			).Should(BeEquivalentTo(1), "only the running EphemeralRunner should remain before listener confirms the larger desired count")
+
+			ers = new(v1alpha1.EphemeralRunnerSet)
+			err = k8sClient.Get(ctx, client.ObjectKey{Name: ephemeralRunnerSet.Name, Namespace: ephemeralRunnerSet.Namespace}, ers)
+			Expect(err).NotTo(HaveOccurred(), "failed to get EphemeralRunnerSet")
+
+			updated = ers.DeepCopy()
+			updated.Spec.Replicas = 3
+			updated.Spec.PatchID = 3
+
+			err = k8sClient.Patch(ctx, updated, client.MergeFrom(ers))
+			Expect(err).NotTo(HaveOccurred(), "failed to update EphemeralRunnerSet")
+
+			runnerList = new(v1alpha1.EphemeralRunnerList)
+			// We should have 3 runners, and have no Succeeded ones after listener confirms.
 			Eventually(
 				func() error {
 					err := listEphemeralRunnersAndRemoveFinalizers(ctx, k8sClient, runnerList, ephemeralRunnerSet.Namespace)
@@ -698,16 +723,16 @@ var _ = Describe("Test EphemeralRunnerSet controller", func() {
 						return err
 					}
 
-					if len(runnerList.Items) != 3 {
-						return fmt.Errorf("Expected 3 runners, got %d", len(runnerList.Items))
-					}
-
 					for _, runner := range runnerList.Items {
 						if runner.Status.Phase == v1alpha1.EphemeralRunnerPhaseSucceeded {
 							return fmt.Errorf("Runner %s is in Succeeded phase", runner.Name)
 						}
 					}
 
+					if len(runnerList.Items) != 3 {
+						return fmt.Errorf("Expected 3 runners, got %d", len(runnerList.Items))
+					}
+
 					return nil
 				},
 				ephemeralRunnerSetTestTimeout,
@@ -1017,7 +1042,7 @@ var _ = Describe("Test EphemeralRunnerSet controller", func() {
 						}
 					}
 
-					if succeeded != 1 && running != 1 {
+					if succeeded != 1 || running != 1 {
 						return fmt.Errorf("Expected 1 runner in Succeeded and 1 in Running, got %d in Succeeded and %d in Running", succeeded, running)
 					}
 
@@ -1027,8 +1052,9 @@ var _ = Describe("Test EphemeralRunnerSet controller", func() {
 				ephemeralRunnerSetTestInterval,
 			).Should(BeNil(), "1 EphemeralRunner should be in Succeeded and 1 in Running phase")
 
-			// Now, let's simulate replacement. The desired count is still 2.
-			// This simulates that we got 1 job assigned, and 1 job completed.
+			// Now, let's simulate the listener publishing a stale patch before it has
+			// accounted for the completed job. The controller should clean up the
+			// finished runner but not create a replacement for this patch.
 
 			ers = new(v1alpha1.EphemeralRunnerSet)
 			err = k8sClient.Get(ctx, client.ObjectKey{Name: ephemeralRunnerSet.Name, Namespace: ephemeralRunnerSet.Namespace}, ers)
@@ -1041,6 +1067,46 @@ var _ = Describe("Test EphemeralRunnerSet controller", func() {
 			err = k8sClient.Patch(ctx, updated, client.MergeFrom(ers))
 			Expect(err).NotTo(HaveOccurred(), "failed to update EphemeralRunnerSet")
 
+			runnerList = new(v1alpha1.EphemeralRunnerList)
+			Eventually(
+				func() (int, error) {
+					err := listEphemeralRunnersAndRemoveFinalizers(ctx, k8sClient, runnerList, ephemeralRunnerSet.Namespace)
+					if err != nil {
+						return -1, err
+					}
+
+					return len(runnerList.Items), nil
+				},
+				ephemeralRunnerSetTestTimeout,
+				ephemeralRunnerSetTestInterval,
+			).Should(BeEquivalentTo(1), "the finished EphemeralRunner should be cleaned up")
+
+			Consistently(
+				func() (int, error) {
+					err := listEphemeralRunnersAndRemoveFinalizers(ctx, k8sClient, runnerList, ephemeralRunnerSet.Namespace)
+					if err != nil {
+						return -1, err
+					}
+
+					return len(runnerList.Items), nil
+				},
+				2*time.Second,
+				ephemeralRunnerSetTestInterval,
+			).Should(BeEquivalentTo(1), "only the running EphemeralRunner should remain before listener confirms replacement")
+
+			// A fresh listener decision with the same desired count confirms that a
+			// replacement is still needed.
+			ers = new(v1alpha1.EphemeralRunnerSet)
+			err = k8sClient.Get(ctx, client.ObjectKey{Name: ephemeralRunnerSet.Name, Namespace: ephemeralRunnerSet.Namespace}, ers)
+			Expect(err).NotTo(HaveOccurred(), "failed to get EphemeralRunnerSet")
+
+			updated = ers.DeepCopy()
+			updated.Spec.Replicas = 2
+			updated.Spec.PatchID = 3
+
+			err = k8sClient.Patch(ctx, updated, client.MergeFrom(ers))
+			Expect(err).NotTo(HaveOccurred(), "failed to update EphemeralRunnerSet")
+
 			runnerList = new(v1alpha1.EphemeralRunnerList)
 			Eventually(
 				func() error {
@@ -1066,6 +1132,315 @@ var _ = Describe("Test EphemeralRunnerSet controller", func() {
 			).Should(BeNil(), "2 EphemeralRunner should be created and none should be in Succeeded phase")
 		})
 
+		It("Should not create a replacement when a runner finishes ahead of the listener decrement patch", func() {
+			ers := new(v1alpha1.EphemeralRunnerSet)
+			err := k8sClient.Get(ctx, client.ObjectKey{Name: ephemeralRunnerSet.Name, Namespace: ephemeralRunnerSet.Namespace}, ers)
+			Expect(err).NotTo(HaveOccurred(), "failed to get EphemeralRunnerSet")
+
+			updated := ers.DeepCopy()
+			updated.Spec.Replicas = 4
+			updated.Spec.PatchID = 1
+
+			err = k8sClient.Patch(ctx, updated, client.MergeFrom(ers))
+			Expect(err).NotTo(HaveOccurred(), "failed to update EphemeralRunnerSet")
+
+			runnerList := new(v1alpha1.EphemeralRunnerList)
+			Eventually(
+				func() (int, error) {
+					err := listEphemeralRunnersAndRemoveFinalizers(ctx, k8sClient, runnerList, ephemeralRunnerSet.Namespace)
+					if err != nil {
+						return -1, err
+					}
+
+					return len(runnerList.Items), nil
+				},
+				ephemeralRunnerSetTestTimeout,
+				ephemeralRunnerSetTestInterval,
+			).Should(BeEquivalentTo(4), "4 EphemeralRunner should be created")
+
+			for i := range 3 {
+				updatedRunner := runnerList.Items[i].DeepCopy()
+				updatedRunner.Status.Phase = v1alpha1.EphemeralRunnerPhaseRunning
+				err = k8sClient.Status().Patch(ctx, updatedRunner, client.MergeFrom(&runnerList.Items[i]))
+				Expect(err).NotTo(HaveOccurred(), "failed to update EphemeralRunner")
+			}
+
+			updatedRunner := runnerList.Items[3].DeepCopy()
+			updatedRunner.Status.Phase = v1alpha1.EphemeralRunnerPhaseSucceeded
+			err = k8sClient.Status().Patch(ctx, updatedRunner, client.MergeFrom(&runnerList.Items[3]))
+			Expect(err).NotTo(HaveOccurred(), "failed to update EphemeralRunner")
+
+			ers = new(v1alpha1.EphemeralRunnerSet)
+			err = k8sClient.Get(ctx, client.ObjectKey{Name: ephemeralRunnerSet.Name, Namespace: ephemeralRunnerSet.Namespace}, ers)
+			Expect(err).NotTo(HaveOccurred(), "failed to get EphemeralRunnerSet")
+
+			updated = ers.DeepCopy()
+			updated.Spec.Replicas = 4
+			updated.Spec.PatchID = 2
+
+			err = k8sClient.Patch(ctx, updated, client.MergeFrom(ers))
+			Expect(err).NotTo(HaveOccurred(), "failed to update EphemeralRunnerSet")
+
+			Eventually(
+				func() (int, error) {
+					err := listEphemeralRunnersAndRemoveFinalizers(ctx, k8sClient, runnerList, ephemeralRunnerSet.Namespace)
+					if err != nil {
+						return -1, err
+					}
+
+					return len(runnerList.Items), nil
+				},
+				ephemeralRunnerSetTestTimeout,
+				ephemeralRunnerSetTestInterval,
+			).Should(BeEquivalentTo(3), "only the running EphemeralRunners should remain after stale-patch cleanup")
+
+			ers = new(v1alpha1.EphemeralRunnerSet)
+			err = k8sClient.Get(ctx, client.ObjectKey{Name: ephemeralRunnerSet.Name, Namespace: ephemeralRunnerSet.Namespace}, ers)
+			Expect(err).NotTo(HaveOccurred(), "failed to get EphemeralRunnerSet")
+			Expect(ers.Status.FinishedRunnerCleanupPatchID).To(BeEquivalentTo(2), "the cleanup should be recorded against the patch ID it was performed for")
+
+			Consistently(
+				func() (int, error) {
+					err := listEphemeralRunnersAndRemoveFinalizers(ctx, k8sClient, runnerList, ephemeralRunnerSet.Namespace)
+					if err != nil {
+						return -1, err
+					}
+
+					return len(runnerList.Items), nil
+				},
+				12*time.Second,
+				ephemeralRunnerSetTestInterval,
+			).Should(BeEquivalentTo(3), "EphemeralRunnerSet should not create a replacement before listener decrements")
+
+			ers = new(v1alpha1.EphemeralRunnerSet)
+			err = k8sClient.Get(ctx, client.ObjectKey{Name: ephemeralRunnerSet.Name, Namespace: ephemeralRunnerSet.Namespace}, ers)
+			Expect(err).NotTo(HaveOccurred(), "failed to get EphemeralRunnerSet")
+
+			updated = ers.DeepCopy()
+			updated.Spec.Replicas = 3
+			updated.Spec.PatchID = 3
+
+			err = k8sClient.Patch(ctx, updated, client.MergeFrom(ers))
+			Expect(err).NotTo(HaveOccurred(), "failed to update EphemeralRunnerSet")
+
+			runnerList = new(v1alpha1.EphemeralRunnerList)
+			Eventually(
+				func() (int, error) {
+					err := listEphemeralRunnersAndRemoveFinalizers(ctx, k8sClient, runnerList, ephemeralRunnerSet.Namespace)
+					if err != nil {
+						return -1, err
+					}
+
+					return len(runnerList.Items), nil
+				},
+				ephemeralRunnerSetTestTimeout,
+				ephemeralRunnerSetTestInterval,
+			).Should(BeEquivalentTo(3), "EphemeralRunnerSet should converge after listener decrements")
+		})
+
+		It("Should resume scaling up once the listener publishes a new patch ID after cleanup", func() {
+			ers := new(v1alpha1.EphemeralRunnerSet)
+			err := k8sClient.Get(ctx, client.ObjectKey{Name: ephemeralRunnerSet.Name, Namespace: ephemeralRunnerSet.Namespace}, ers)
+			Expect(err).NotTo(HaveOccurred(), "failed to get EphemeralRunnerSet")
+
+			updated := ers.DeepCopy()
+			updated.Spec.Replicas = 2
+			updated.Spec.PatchID = 1
+
+			err = k8sClient.Patch(ctx, updated, client.MergeFrom(ers))
+			Expect(err).NotTo(HaveOccurred(), "failed to update EphemeralRunnerSet")
+
+			runnerList := new(v1alpha1.EphemeralRunnerList)
+			Eventually(
+				func() (int, error) {
+					err := listEphemeralRunnersAndRemoveFinalizers(ctx, k8sClient, runnerList, ephemeralRunnerSet.Namespace)
+					if err != nil {
+						return -1, err
+					}
+
+					return len(runnerList.Items), nil
+				},
+				ephemeralRunnerSetTestTimeout,
+				ephemeralRunnerSetTestInterval,
+			).Should(BeEquivalentTo(2), "2 EphemeralRunner should be created")
+
+			// Both runners finish. The next patch still asks for 2, but it was
+			// computed before the completions, so it must not cause replacements.
+			for i := range 2 {
+				updatedRunner := runnerList.Items[i].DeepCopy()
+				updatedRunner.Status.Phase = v1alpha1.EphemeralRunnerPhaseSucceeded
+				err = k8sClient.Status().Patch(ctx, updatedRunner, client.MergeFrom(&runnerList.Items[i]))
+				Expect(err).NotTo(HaveOccurred(), "failed to update EphemeralRunner")
+			}
+
+			ers = new(v1alpha1.EphemeralRunnerSet)
+			err = k8sClient.Get(ctx, client.ObjectKey{Name: ephemeralRunnerSet.Name, Namespace: ephemeralRunnerSet.Namespace}, ers)
+			Expect(err).NotTo(HaveOccurred(), "failed to get EphemeralRunnerSet")
+
+			updated = ers.DeepCopy()
+			updated.Spec.Replicas = 2
+			updated.Spec.PatchID = 2
+
+			err = k8sClient.Patch(ctx, updated, client.MergeFrom(ers))
+			Expect(err).NotTo(HaveOccurred(), "failed to update EphemeralRunnerSet")
+
+			Eventually(
+				func() (int, error) {
+					err := listEphemeralRunnersAndRemoveFinalizers(ctx, k8sClient, runnerList, ephemeralRunnerSet.Namespace)
+					if err != nil {
+						return -1, err
+					}
+
+					return len(runnerList.Items), nil
+				},
+				ephemeralRunnerSetTestTimeout,
+				ephemeralRunnerSetTestInterval,
+			).Should(BeEquivalentTo(0), "both finished EphemeralRunners should be cleaned up")
+
+			Consistently(
+				func() (int, error) {
+					err := listEphemeralRunnersAndRemoveFinalizers(ctx, k8sClient, runnerList, ephemeralRunnerSet.Namespace)
+					if err != nil {
+						return -1, err
+					}
+
+					return len(runnerList.Items), nil
+				},
+				10*time.Second,
+				ephemeralRunnerSetTestInterval,
+			).Should(BeEquivalentTo(0), "scale up should stay suppressed for the patch ID the cleanup was performed for")
+
+			// The listener now publishes a fresh desired state that still wants 2
+			// runners. This is genuine demand, so the controller must act on it.
+			ers = new(v1alpha1.EphemeralRunnerSet)
+			err = k8sClient.Get(ctx, client.ObjectKey{Name: ephemeralRunnerSet.Name, Namespace: ephemeralRunnerSet.Namespace}, ers)
+			Expect(err).NotTo(HaveOccurred(), "failed to get EphemeralRunnerSet")
+
+			updated = ers.DeepCopy()
+			updated.Spec.Replicas = 2
+			updated.Spec.PatchID = 3
+
+			err = k8sClient.Patch(ctx, updated, client.MergeFrom(ers))
+			Expect(err).NotTo(HaveOccurred(), "failed to update EphemeralRunnerSet")
+
+			Eventually(
+				func() (int, error) {
+					err := listEphemeralRunnersAndRemoveFinalizers(ctx, k8sClient, runnerList, ephemeralRunnerSet.Namespace)
+					if err != nil {
+						return -1, err
+					}
+
+					return len(runnerList.Items), nil
+				},
+				ephemeralRunnerSetTestTimeout,
+				ephemeralRunnerSetTestInterval,
+			).Should(BeEquivalentTo(2), "scale up should resume once a fresh patch ID arrives")
+		})
+
+		It("Should count runners that are still being deleted when scaling up", func() {
+			ers := new(v1alpha1.EphemeralRunnerSet)
+			err := k8sClient.Get(ctx, client.ObjectKey{Name: ephemeralRunnerSet.Name, Namespace: ephemeralRunnerSet.Namespace}, ers)
+			Expect(err).NotTo(HaveOccurred(), "failed to get EphemeralRunnerSet")
+
+			updated := ers.DeepCopy()
+			updated.Spec.Replicas = 2
+			updated.Spec.PatchID = 1
+
+			err = k8sClient.Patch(ctx, updated, client.MergeFrom(ers))
+			Expect(err).NotTo(HaveOccurred(), "failed to update EphemeralRunnerSet")
+
+			runnerList := new(v1alpha1.EphemeralRunnerList)
+			Eventually(
+				func() (int, error) {
+					err := listEphemeralRunnersAndRemoveFinalizers(ctx, k8sClient, runnerList, ephemeralRunnerSet.Namespace)
+					if err != nil {
+						return -1, err
+					}
+
+					return len(runnerList.Items), nil
+				},
+				ephemeralRunnerSetTestTimeout,
+				ephemeralRunnerSetTestInterval,
+			).Should(BeEquivalentTo(2), "2 EphemeralRunner should be created")
+
+			for i := range 2 {
+				updatedRunner := runnerList.Items[i].DeepCopy()
+				updatedRunner.Status.Phase = v1alpha1.EphemeralRunnerPhaseRunning
+				err = k8sClient.Status().Patch(ctx, updatedRunner, client.MergeFrom(&runnerList.Items[i]))
+				Expect(err).NotTo(HaveOccurred(), "failed to update EphemeralRunner")
+			}
+
+			// Delete one runner but leave its finalizer in place, so it lingers in
+			// the deleting state the way a runner does while it unregisters.
+			deleting := runnerList.Items[0].DeepCopy()
+			err = k8sClient.Delete(ctx, deleting)
+			Expect(err).NotTo(HaveOccurred(), "failed to delete EphemeralRunner")
+
+			ers = new(v1alpha1.EphemeralRunnerSet)
+			err = k8sClient.Get(ctx, client.ObjectKey{Name: ephemeralRunnerSet.Name, Namespace: ephemeralRunnerSet.Namespace}, ers)
+			Expect(err).NotTo(HaveOccurred(), "failed to get EphemeralRunnerSet")
+
+			updated = ers.DeepCopy()
+			updated.Spec.Replicas = 2
+			updated.Spec.PatchID = 2
+
+			err = k8sClient.Patch(ctx, updated, client.MergeFrom(ers))
+			Expect(err).NotTo(HaveOccurred(), "failed to update EphemeralRunnerSet")
+
+			Consistently(
+				func() (int, error) {
+					list := new(v1alpha1.EphemeralRunnerList)
+					if err := k8sClient.List(ctx, list, client.InNamespace(ephemeralRunnerSet.Namespace)); err != nil {
+						return -1, err
+					}
+
+					return len(list.Items), nil
+				},
+				10*time.Second,
+				ephemeralRunnerSetTestInterval,
+			).Should(BeEquivalentTo(2), "the runner being deleted should count towards the desired replicas, so no replacement is created")
+
+			// Let the deletion complete. Now the count really is below the desired
+			// replicas, and the next patch should top it back up.
+			runnerList = new(v1alpha1.EphemeralRunnerList)
+			Eventually(
+				func() (int, error) {
+					err := listEphemeralRunnersAndRemoveFinalizers(ctx, k8sClient, runnerList, ephemeralRunnerSet.Namespace)
+					if err != nil {
+						return -1, err
+					}
+
+					return len(runnerList.Items), nil
+				},
+				ephemeralRunnerSetTestTimeout,
+				ephemeralRunnerSetTestInterval,
+			).Should(BeEquivalentTo(1), "only the running EphemeralRunner should remain")
+
+			ers = new(v1alpha1.EphemeralRunnerSet)
+			err = k8sClient.Get(ctx, client.ObjectKey{Name: ephemeralRunnerSet.Name, Namespace: ephemeralRunnerSet.Namespace}, ers)
+			Expect(err).NotTo(HaveOccurred(), "failed to get EphemeralRunnerSet")
+
+			updated = ers.DeepCopy()
+			updated.Spec.Replicas = 2
+			updated.Spec.PatchID = 3
+
+			err = k8sClient.Patch(ctx, updated, client.MergeFrom(ers))
+			Expect(err).NotTo(HaveOccurred(), "failed to update EphemeralRunnerSet")
+
+			Eventually(
+				func() (int, error) {
+					err := listEphemeralRunnersAndRemoveFinalizers(ctx, k8sClient, runnerList, ephemeralRunnerSet.Namespace)
+					if err != nil {
+						return -1, err
+					}
+
+					return len(runnerList.Items), nil
+				},
+				ephemeralRunnerSetTestTimeout,
+				ephemeralRunnerSetTestInterval,
+			).Should(BeEquivalentTo(2), "the replacement should be created once the deletion completes")
+		})
+
 		It("Should delete idle runners, keep busy runners, and create new runners when the spec changes", func() {
 			ers := new(v1alpha1.EphemeralRunnerSet)
 			err := k8sClient.Get(ctx, client.ObjectKey{Name: ephemeralRunnerSet.Name, Namespace: ephemeralRunnerSet.Namespace}, ers)