Validate machineset before reconciling

Even thought the MachineSet type implements Validate() function,
it's not called by default. The validation function is responsible
for making sure every machine set matchLabels selector is matched with
machine template labels. Given the validation is not performed by default,
it is possible to create an invalid machineset that causes the machineset
controller to start creating machine object one by one without any upper
bound. Causing the machine controller to launch as many instances as
there is machine objects.

pkg/controller/machinedeployment/machinedeployment_controller_test.go

@@ -17,6 +17,7 @@ limitations under the License.
 package machinedeployment
 
 import (
+	"fmt"
 	"testing"
 	"time"
 
@@ -174,6 +175,7 @@ func TestReconcile(t *testing.T) {
 		expectInt(t, i, func(ctx context.Context) int {
 			if err = c.Get(ctx, types.NamespacedName{
 				Namespace: newMachineSet.Namespace, Name: newMachineSet.Name}, newMachineSet); err != nil {
+				fmt.Printf("err: %v\n", err)
 				return -1
 			}
 			return int(*newMachineSet.Spec.Replicas)

pkg/controller/machineset/controller.go

@@ -150,6 +150,13 @@ func (r *ReconcileMachineSet) Reconcile(request reconcile.Request) (reconcile.Re
 	}
 
 	klog.V(4).Infof("Reconcile machineset %v", machineSet.Name)
+
+	if errList := machineSet.Validate(); len(errList) > 0 {
+		err := fmt.Errorf("%q machineset validation failed: %v", machineSet.Name, errList.ToAggregate().Error())
+		klog.Error(err)
+		return reconcile.Result{}, err
+	}
+
 	allMachines := &clusterv1alpha1.MachineList{}
 
 	err = r.Client.List(context.Background(), client.InNamespace(machineSet.Namespace), allMachines)

pkg/controller/machineset/machineset_controller_test.go

@@ -37,11 +37,18 @@ const timeout = time.Second * 5
 
 func TestReconcile(t *testing.T) {
 	replicas := int32(2)
+	labels := map[string]string{"foo": "bar"}
 	instance := &clusterv1alpha1.MachineSet{
 		ObjectMeta: metav1.ObjectMeta{Name: "foo", Namespace: "default"},
 		Spec: clusterv1alpha1.MachineSetSpec{
 			Replicas: &replicas,
+			Selector: metav1.LabelSelector{
+				MatchLabels: labels,
+			},
 			Template: clusterv1alpha1.MachineTemplateSpec{
+				ObjectMeta: metav1.ObjectMeta{
+					Labels: labels,
+				},
 				Spec: clusterv1alpha1.MachineSpec{
 					Versions: clusterv1alpha1.MachineVersionInfo{Kubelet: "1.10.3"},
 				},