Allow karpenter to set arbitrary k8s labels on NodeClaim/Nodes

nodeClaim Labels are the source for core karpenter to sync Node Labels in a centralized fashion.
Some bootstrap userdata provider implementations also consume this labels and pass them through kubelet self setting.
That results in a coupling between a centralized and a kubelet self setting approach.
This coupling results in conflicting criteria for validations and degraded UX.
This PR removes the coupling.
As a consequence, Node Labels are not unncessarily restricted for the centralized sync anymore.
This better empowers administrators reducing the reliance on self setting kubelet and minimizing the risk of a Node steering privileged workloads to itself.

A subset of labels, excluding those disallowed by the node restriction admission, is now stored in json within the "karpenter.sh/kubelet-labels" NodeClaim annotation.
This enables bootstrap userdata providers to continue utilizing the labels if needed.

Author: enxebre

pkg/apis/v1/labels.go

@@ -58,22 +58,17 @@ const (
 )
 
 var (
-	// RestrictedLabelDomains are either prohibited by the kubelet or reserved by karpenter
+	// RestrictedLabelDomains are reserved by karpenter
 	RestrictedLabelDomains = sets.New(
-		"kubernetes.io",
-		"k8s.io",
 		apis.Group,
 	)
 
-	// LabelDomainExceptions are sub-domains of the RestrictedLabelDomains but allowed because
-	// they are not used in a context where they may be passed as argument to kubelet.
-	LabelDomainExceptions = sets.New(
-		"kops.k8s.io",
-		v1.LabelNamespaceSuffixNode,
-		v1.LabelNamespaceNodeRestriction,
+	K8sLabelDomains = sets.New(
+		"kubernetes.io",
+		"k8s.io",
 	)
 
-	// WellKnownLabels are labels that belong to the RestrictedLabelDomains but allowed.
+	// WellKnownLabels are labels that belong to the RestrictedLabelDomains or K8sLabelDomains but allowed.
 	// Karpenter is aware of these labels, and they can be used to further narrow down
 	// the range of the corresponding values by either nodepool or pods.
 	WellKnownLabels = sets.New(
@@ -104,38 +99,90 @@ var (
 	}
 )
 
-// IsRestrictedLabel returns an error if the label is restricted.
+// IsRestrictedLabel is used for runtime validation of requirements.
+// Returns an error if the label is restricted. E.g. using .karpenter.sh suffix.
 func IsRestrictedLabel(key string) error {
 	if WellKnownLabels.Has(key) {
 		return nil
 	}
-	if IsRestrictedNodeLabel(key) {
+
+	labelDomain := GetLabelDomain(key)
+	for restrictedLabelDomain := range RestrictedLabelDomains {
+		if labelDomain == restrictedLabelDomain || strings.HasSuffix(labelDomain, "."+restrictedLabelDomain) {
+			return fmt.Errorf("label %s is restricted; specify a well known label: %v, or a custom label that does not use a restricted domain: %v", key, sets.List(WellKnownLabels), sets.List(RestrictedLabelDomains))
+		}
+	}
+
+	if RestrictedLabels.Has(key) {
 		return fmt.Errorf("label %s is restricted; specify a well known label: %v, or a custom label that does not use a restricted domain: %v", key, sets.List(WellKnownLabels), sets.List(RestrictedLabelDomains))
 	}
+
 	return nil
 }
 
-// IsRestrictedNodeLabel returns true if a node label should not be injected by Karpenter.
-// They are either known labels that will be injected by cloud providers,
-// or label domain managed by other software (e.g., kops.k8s.io managed by kOps).
-func IsRestrictedNodeLabel(key string) bool {
+// IsValidLabelToSync returns true if the label key is allowed to be synced to the Node object centrally by Karpenter.
+func IsValidToSyncCentrallyLabel(key string) bool {
+	// TODO(enxebre): consider this to be configurable with runtime flag.
+	notValidToSyncLabel := sets.New(
+		v1.LabelHostname,
+		v1.LabelArchStable,
+		v1.LabelOSStable,
+		v1.LabelInstanceTypeStable,
+		v1.LabelWindowsBuild,
+	)
+
+	if notValidToSyncLabel.Has(key) {
+		return false
+	}
+
+	return true
+}
+
+// IsKubeletLabel returns true if the label key is one that kubelets are allowed to set on their own Node object.
+// This function is similar the one used by the node restriction admission https://github.com/kubernetes/kubernetes/blob/e319c541f144e9bee6160f1dd8671638a9029f4c/staging/src/k8s.io/kubelet/pkg/apis/well_known_labels.go#L67
+// but karpenter also restricts the known labels to be passed to kubelet. Only the kubeletLabelNamespaces are allowed.
+func IsKubeletLabel(key string) bool {
 	if WellKnownLabels.Has(key) {
-		return true
+		return false
 	}
-	labelDomain := GetLabelDomain(key)
-	for exceptionLabelDomain := range LabelDomainExceptions {
-		if strings.HasSuffix(labelDomain, exceptionLabelDomain) {
-			return false
-		}
+
+	if !isKubernetesLabel(key) {
+		return true
 	}
-	for restrictedLabelDomain := range RestrictedLabelDomains {
-		if strings.HasSuffix(labelDomain, restrictedLabelDomain) {
+
+	namespace := getLabelNamespace(key)
+	for allowedNamespace := range kubeletLabelNamespaces {
+		if namespace == allowedNamespace || strings.HasSuffix(namespace, "."+allowedNamespace) {
 			return true
 		}
 	}
-	return RestrictedLabels.Has(key)
+
+	return false
+}
+
+func isKubernetesLabel(key string) bool {
+	namespace := getLabelNamespace(key)
+	if namespace == "kubernetes.io" || strings.HasSuffix(namespace, ".kubernetes.io") {
+		return true
+	}
+	if namespace == "k8s.io" || strings.HasSuffix(namespace, ".k8s.io") {
+		return true
+	}
+	return false
 }
 
+func getLabelNamespace(key string) string {
+	if parts := strings.SplitN(key, "/", 2); len(parts) == 2 {
+		return parts[0]
+	}
+	return ""
+}
+
+var kubeletLabelNamespaces = sets.NewString(
+	v1.LabelNamespaceSuffixKubelet,
+	v1.LabelNamespaceSuffixNode,
+)
+
 func GetLabelDomain(key string) string {
 	if parts := strings.SplitN(key, "/", 2); len(parts) == 2 {
 		return parts[0]

pkg/controllers/nodeclaim/lifecycle/launch.go

@@ -18,6 +18,7 @@ package lifecycle
 
 import (
 	"context"
+	"encoding/json"
 	"errors"
 	"fmt"
 
@@ -28,6 +29,7 @@ import (
 	"sigs.k8s.io/controller-runtime/pkg/log"
 	"sigs.k8s.io/controller-runtime/pkg/reconcile"
 
+	"sigs.k8s.io/karpenter/pkg/apis"
 	v1 "sigs.k8s.io/karpenter/pkg/apis/v1"
 	"sigs.k8s.io/karpenter/pkg/cloudprovider"
 	"sigs.k8s.io/karpenter/pkg/events"
@@ -127,7 +129,14 @@ func PopulateNodeClaimDetails(nodeClaim, retrieved *v1.NodeClaim) *v1.NodeClaim
 		scheduling.NewNodeSelectorRequirementsWithMinValues(nodeClaim.Spec.Requirements...).Labels(), // Single-value requirement resolved labels
 		nodeClaim.Labels, // User-defined labels
 	)
-	nodeClaim.Annotations = lo.Assign(nodeClaim.Annotations, retrieved.Annotations)
+
+	kubeletLabels := scheduling.NewNodeSelectorRequirementsWithMinValues(nodeClaim.Spec.Requirements...).KubeletLabels()
+	json, err := json.Marshal(kubeletLabels)
+	if err != nil {
+		panic(err)
+	}
+	kubeletLabelsAnnotation := map[string]string{apis.Group + "/node-restricted-labels": string(json)}
+	nodeClaim.Annotations = lo.Assign(nodeClaim.Annotations, retrieved.Annotations, kubeletLabelsAnnotation)
 	nodeClaim.Status.ProviderID = retrieved.Status.ProviderID
 	nodeClaim.Status.ImageID = retrieved.Status.ImageID
 	nodeClaim.Status.Allocatable = retrieved.Status.Allocatable

pkg/scheduling/requirements.go

@@ -303,13 +303,29 @@ func (r Requirements) Intersects(requirements Requirements) (errs error) {
 	return errs
 }
 
+// Labels filters out labels from the requirements that are not allowed to be synced centrally by Karpenter to the Node.
 func (r Requirements) Labels() map[string]string {
 	labels := map[string]string{}
 	for key, requirement := range r {
-		if !v1.IsRestrictedNodeLabel(key) {
-			if value := requirement.Any(); value != "" {
-				labels[key] = value
-			}
+		if !v1.IsValidToSyncCentrallyLabel(key) {
+			continue
+		}
+		if value := requirement.Any(); value != "" {
+			labels[key] = value
+		}
+	}
+	return labels
+}
+
+// KubeletLabels filters out labels from the requirements that will be rejected by the node restriction admission.
+func (r Requirements) KubeletLabels() map[string]string {
+	labels := map[string]string{}
+	for key, requirement := range r {
+		if !v1.IsKubeletLabel(key) {
+			continue
+		}
+		if value := requirement.Any(); value != "" {
+			labels[key] = value
 		}
 	}
 	return labels