In-place Pod Vertical Scaling - API changes

1. Define ContainerResizePolicy and add it to Container struct.
 2. Add ResourcesAllocated and Resources fields to ContainerStatus struct.
 3. Define ResourcesResizeStatus and add it to PodStatus struct.
 4. Add InPlacePodVerticalScaling feature gate and drop disabled fields.
 5. ResizePolicy validation & defaulting and Resources mutability for CPU/Memory.
 6. Various fixes from code review feedback (originally committed on Apr 12, 2022)
KEP: /enhancements/keps/sig-node/1287-in-place-update-pod-resources

Kubernetes-commit: 76962b0fa7862727e93ef591f4b0822c8d80534b

pkg/admission/plugin/resourcequota/controller.go

@@ -35,8 +35,10 @@ import (
 	"k8s.io/apimachinery/pkg/util/wait"
 	"k8s.io/apiserver/pkg/admission"
 	resourcequotaapi "k8s.io/apiserver/pkg/admission/plugin/resourcequota/apis/resourcequota"
+	"k8s.io/apiserver/pkg/features"
 	quota "k8s.io/apiserver/pkg/quota/v1"
 	"k8s.io/apiserver/pkg/quota/v1/generic"
+	"k8s.io/apiserver/pkg/util/feature"
 	"k8s.io/client-go/util/workqueue"
 )
 
@@ -516,7 +518,14 @@ func CheckRequest(quotas []corev1.ResourceQuota, a admission.Attributes, evaluat
 			if innerErr != nil {
 				return quotas, innerErr
 			}
-			deltaUsage = quota.SubtractWithNonNegativeResult(deltaUsage, prevUsage)
+			if feature.DefaultFeatureGate.Enabled(features.InPlacePodVerticalScaling) {
+				// allow negative usage for pods as pod resources can increase or decrease
+				if a.GetResource().GroupResource() == corev1.Resource("pods") {
+					deltaUsage = quota.Subtract(deltaUsage, prevUsage)
+				}
+			} else {
+				deltaUsage = quota.SubtractWithNonNegativeResult(deltaUsage, prevUsage)
+			}
 		}
 	}
 

pkg/features/kube_features.go

@@ -198,6 +198,13 @@ const (
 	//
 	// Enables support for watch bookmark events.
 	WatchBookmark featuregate.Feature = "WatchBookmark"
+
+	// owner: @vinaykul
+	// kep: http://kep.k8s.io/1287
+	// alpha: v1.27
+	//
+	// Enables In-Place Pod Vertical Scaling
+	InPlacePodVerticalScaling featuregate.Feature = "InPlacePodVerticalScaling"
 )
 
 func init() {
@@ -249,4 +256,6 @@ var defaultKubernetesFeatureGates = map[featuregate.Feature]featuregate.FeatureS
 	StorageVersionHash: {Default: true, PreRelease: featuregate.Beta},
 
 	WatchBookmark: {Default: true, PreRelease: featuregate.GA, LockToDefault: true},
+
+	InPlacePodVerticalScaling: {Default: false, PreRelease: featuregate.Alpha},
 }