MachinePool annotation for externally managed autoscaler

api/v1beta1/common_types.go

@@ -126,6 +126,10 @@ const (
 	// any changes to the actual object because it is a dry run) and the topology controller
 	// will receive the resulting object.
 	TopologyDryRunAnnotation = "topology.cluster.x-k8s.io/dry-run"
+
+	// ReplicasManagedByAutoscalerAnnotation is an annotation that indicates an external autoscaler controls replica count.
+	// This annotation can be used to inform MachinePool status during in-progress scaling scenarios.
+	ReplicasManagedByAutoscalerAnnotation = "cluster.x-k8s.io/replicas-managed-by-autoscaler"
 )
 
 const (

exp/internal/controllers/machinepool_controller_phases.go

@@ -69,12 +69,20 @@ func (r *MachinePoolReconciler) reconcilePhase(mp *expv1.MachinePool) {
 
 	// Set the phase to "scalingUp" if the infrastructure is scaling up.
 	if mp.Status.InfrastructureReady && *mp.Spec.Replicas > mp.Status.ReadyReplicas {
-		mp.Status.SetTypedPhase(expv1.MachinePoolPhaseScalingUp)
+		if mp.Annotations[clusterv1.ReplicasManagedByAutoscalerAnnotation] == "true" {
+			mp.Status.SetTypedPhase(expv1.MachinePoolPhasePending)
+		} else {
+			mp.Status.SetTypedPhase(expv1.MachinePoolPhaseScalingUp)
+		}
 	}
 
 	// Set the phase to "scalingDown" if the infrastructure is scaling down.
 	if mp.Status.InfrastructureReady && *mp.Spec.Replicas < mp.Status.ReadyReplicas {
-		mp.Status.SetTypedPhase(expv1.MachinePoolPhaseScalingDown)
+		if mp.Annotations[clusterv1.ReplicasManagedByAutoscalerAnnotation] == "true" {
+			mp.Status.SetTypedPhase(expv1.MachinePoolPhasePending)
+		} else {
+			mp.Status.SetTypedPhase(expv1.MachinePoolPhaseScalingDown)
+		}
 	}
 
 	// Set the phase to "failed" if any of Status.FailureReason or Status.FailureMessage is not-nil.