Tighten validation on the qosClass field of pod status

Author: carlory

pkg/apis/core/validation/validation.go

@@ -5373,6 +5373,9 @@ func ValidatePodStatusUpdate(newPod, oldPod *core.Pod, opts PodValidationOptions
 		}
 	}
 
+	// Pod QoS is immutable
+	allErrs = append(allErrs, ValidateImmutableField(newPod.Status.QOSClass, oldPod.Status.QOSClass, fldPath.Child("qosClass"))...)
+
 	// If pod should not restart, make sure the status update does not transition
 	// any terminated containers to a non-terminated state.
 	allErrs = append(allErrs, ValidateContainerStateTransition(newPod.Status.ContainerStatuses, oldPod.Status.ContainerStatuses, fldPath.Child("containerStatuses"), oldPod.Spec.RestartPolicy)...)

pkg/apis/core/validation/validation_test.go

@@ -14454,6 +14454,32 @@ func TestValidatePodStatusUpdate(t *testing.T) {
 		),
 		"",
 		"restartable init container can restart if RestartPolicyAlways",
+	}, {
+		*podtest.MakePod("foo",
+			podtest.SetStatus(core.PodStatus{
+				QOSClass: core.PodQOSBurstable,
+			}),
+		),
+		*podtest.MakePod("foo",
+			podtest.SetStatus(core.PodStatus{
+				QOSClass: core.PodQOSGuaranteed,
+			}),
+		),
+		"tatus.qosClass: Invalid value: \"Burstable\": field is immutable",
+		"qosClass can not be changed",
+	}, {
+		*podtest.MakePod("foo",
+			podtest.SetStatus(core.PodStatus{
+				QOSClass: core.PodQOSBurstable,
+			}),
+		),
+		*podtest.MakePod("foo",
+			podtest.SetStatus(core.PodStatus{
+				QOSClass: core.PodQOSBurstable,
+			}),
+		),
+		"",
+		"qosClass no change",
 	},
 	}
 

pkg/registry/core/pod/strategy.go

@@ -226,6 +226,11 @@ func (podStatusStrategy) PrepareForUpdate(ctx context.Context, obj, old runtime.
 	// don't allow the pods/status endpoint to touch owner references since old kubelets corrupt them in a way
 	// that breaks garbage collection
 	newPod.OwnerReferences = oldPod.OwnerReferences
+	// the Pod QoS is immutable and populated at creation time by the kube-apiserver.
+	// we need to backfill it for backward compatibility because the old kubelet dropped this field when the pod was rejected.
+	if newPod.Status.QOSClass == "" {
+		newPod.Status.QOSClass = oldPod.Status.QOSClass
+	}
 }
 
 func (podStatusStrategy) ValidateUpdate(ctx context.Context, obj, old runtime.Object) field.ErrorList {