Make MachineDeployment.Spec.Strategy a pointer

This is required in order to allow defaulting it via a MutatingWebhook.

When it is a literal and the user creates a MachineDeployment where that
property does not exist, the creation of a jsonpatch will happen based
on a representation where that field exists, since literals always gets
marshaled. This means a generated jsonpatch will get refused by the
APIServer which doesn't know anything about that field with an error
like this: `doc is missing path: "/spec/strategy/type"`

pkg/apis/cluster/v1alpha1/machinedeployment_types.go

@@ -40,7 +40,7 @@ type MachineDeploymentSpec struct {
 	// The deployment strategy to use to replace existing machines with
 	// new ones.
 	// +optional
-	Strategy MachineDeploymentStrategy `json:"strategy,omitempty"`
+	Strategy *MachineDeploymentStrategy `json:"strategy,omitempty"`
 
 	// Minimum number of seconds for which a newly created machine should
 	// be ready.

pkg/controller/machinedeployment/machinedeployment_controller_test.go

@@ -48,7 +48,7 @@ func TestReconcile(t *testing.T) {
 			Replicas:             int32Ptr(2),
 			RevisionHistoryLimit: int32Ptr(0),
 			Selector:             metav1.LabelSelector{MatchLabels: labels},
-			Strategy: clusterv1alpha1.MachineDeploymentStrategy{
+			Strategy: &clusterv1alpha1.MachineDeploymentStrategy{
 				Type: common.RollingUpdateMachineDeploymentStrategyType,
 				RollingUpdate: &clusterv1alpha1.MachineRollingUpdateDeployment{
 					MaxUnavailable: intstrPtr(0),