fix deleting logic

Author: mweibel

azure/scope/strategies/machinepool_deployments/machinepool_deployment_strategy.go

@@ -144,6 +144,11 @@ func (rollingUpdateStrategy rollingUpdateStrategy) SelectMachinesToDelete(ctx co
 		}()
 	)
 
+	// Order AzureMachinePoolMachines with the clusterv1.DeleteMachineAnnotation to the front so that they have delete priority.
+	// This allows MachinePool Machines to work with the autoscaler.
+	failedMachines = orderByDeleteMachineAnnotation(failedMachines)
+	deletingMachines = orderByDeleteMachineAnnotation(deletingMachines)
+
 	log.Info("selecting machines to delete",
 		"readyMachines", len(readyMachines),
 		"desiredReplicaCount", desiredReplicaCount,
@@ -155,18 +160,18 @@ func (rollingUpdateStrategy rollingUpdateStrategy) SelectMachinesToDelete(ctx co
 		"deletingMachines", len(deletingMachines),
 	)
 
-	// if we have machines annotated with delete machine, remove them
-	if len(deleteAnnotatedMachines) > 0 {
-		log.Info("delete annotated machines", "desiredReplicaCount", desiredReplicaCount, "maxUnavailable", maxUnavailable, "deleteAnnotatedMachines", getProviderIDs(deleteAnnotatedMachines))
-		return deleteAnnotatedMachines, nil
-	}
-
 	// if we have failed or deleting machines, remove them
 	if len(failedMachines) > 0 || len(deletingMachines) > 0 {
 		log.Info("failed or deleting machines", "desiredReplicaCount", desiredReplicaCount, "maxUnavailable", maxUnavailable, "failedMachines", getProviderIDs(failedMachines), "deletingMachines", getProviderIDs(deletingMachines))
 		return append(failedMachines, deletingMachines...), nil
 	}
 
+	// if we have machines annotated with delete machine, remove them
+	if len(deleteAnnotatedMachines) > 0 {
+		log.Info("delete annotated machines", "desiredReplicaCount", desiredReplicaCount, "maxUnavailable", maxUnavailable, "deleteAnnotatedMachines", getProviderIDs(deleteAnnotatedMachines))
+		return deleteAnnotatedMachines, nil
+	}
+
 	// if we have not yet reached our desired count, don't try to delete anything
 	if len(readyMachines) < int(desiredReplicaCount) {
 		log.Info("not enough ready machines", "desiredReplicaCount", desiredReplicaCount, "readyMachinesCount", len(readyMachines), "machinesByProviderID", len(machinesByProviderID))
@@ -317,6 +322,18 @@ func orderRandom(machines []infrav1exp.AzureMachinePoolMachine) []infrav1exp.Azu
 	return machines
 }
 
+// orderByDeleteMachineAnnotation will sort AzureMachinePoolMachines with the clusterv1.DeleteMachineAnnotation to the front of the list.
+// It will preserve the existing order of the list otherwise so that it respects the existing delete priority otherwise.
+func orderByDeleteMachineAnnotation(machines []infrav1exp.AzureMachinePoolMachine) []infrav1exp.AzureMachinePoolMachine {
+	sort.SliceStable(machines, func(i, j int) bool {
+		_, iHasAnnotation := machines[i].Annotations[clusterv1.DeleteMachineAnnotation]
+
+		return iHasAnnotation
+	})
+
+	return machines
+}
+
 func getProviderIDs(machines []infrav1exp.AzureMachinePoolMachine) []string {
 	ids := make([]string, len(machines))
 	for i, machine := range machines {