Node lifecycle controller should use a label for excluding nodes

The current mechanism for excluding "master" nodes based on node names
is fragile and should be fixed by using a label exclusion similar to
service load balancers. The legacy code path is preserved behind a
defaulted-on gate and will be removed in the future.

pkg/controller/nodelifecycle/BUILD

@@ -17,7 +17,6 @@ go_library(
         "//pkg/scheduler/api:go_default_library",
         "//pkg/util/metrics:go_default_library",
         "//pkg/util/node:go_default_library",
-        "//pkg/util/system:go_default_library",
         "//pkg/util/taints:go_default_library",
         "//staging/src/k8s.io/api/coordination/v1beta1:go_default_library",
         "//staging/src/k8s.io/api/core/v1:go_default_library",

pkg/controller/nodelifecycle/node_lifecycle_controller.go

@@ -23,13 +23,14 @@ package nodelifecycle
 
 import (
 	"fmt"
+	"strings"
 	"sync"
 	"time"
 
 	"k8s.io/klog"
 
 	coordv1beta1 "k8s.io/api/coordination/v1beta1"
-	"k8s.io/api/core/v1"
+	v1 "k8s.io/api/core/v1"
 	apiequality "k8s.io/apimachinery/pkg/api/equality"
 	apierrors "k8s.io/apimachinery/pkg/api/errors"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
@@ -54,11 +55,11 @@ import (
 	"k8s.io/kubernetes/pkg/controller/nodelifecycle/scheduler"
 	nodeutil "k8s.io/kubernetes/pkg/controller/util/node"
 	"k8s.io/kubernetes/pkg/features"
+	kubefeatures "k8s.io/kubernetes/pkg/features"
 	kubeletapis "k8s.io/kubernetes/pkg/kubelet/apis"
 	schedulerapi "k8s.io/kubernetes/pkg/scheduler/api"
 	"k8s.io/kubernetes/pkg/util/metrics"
 	utilnode "k8s.io/kubernetes/pkg/util/node"
-	"k8s.io/kubernetes/pkg/util/system"
 	taintutils "k8s.io/kubernetes/pkg/util/taints"
 )
 
@@ -715,8 +716,8 @@ func (nc *Controller) monitorNodeHealth() error {
 			continue
 		}
 
-		// We do not treat a master node as a part of the cluster for network disruption checking.
+		// Some nodes may be excluded from disruption checking
-		if !system.IsMasterNode(node.Name) {
+		if !isNodeExcludedFromDisruptionChecks(node) {
 			zoneToNodeConditions[utilnode.GetZoneKey(node)] = append(zoneToNodeConditions[utilnode.GetZoneKey(node)], currentReadyCondition)
 		}
 
@@ -806,6 +807,45 @@ func (nc *Controller) monitorNodeHealth() error {
 	return nil
 }
 
+// labelNodeDisruptionExclusion is a label on nodes that controls whether they are
+// excluded from being considered for disruption checks by the node controller.
+const labelNodeDisruptionExclusion = "node.kubernetes.io/exclude-disruption"
+
+func isNodeExcludedFromDisruptionChecks(node *v1.Node) bool {
+	// DEPRECATED: will be removed in 1.19
+	if utilfeature.DefaultFeatureGate.Enabled(kubefeatures.LegacyNodeRoleBehavior) {
+		if legacyIsMasterNode(node.Name) {
+			return true
+		}
+	}
+	if utilfeature.DefaultFeatureGate.Enabled(kubefeatures.NodeDisruptionExclusion) {
+		if _, ok := node.Labels[labelNodeDisruptionExclusion]; ok {
+			return true
+		}
+	}
+	return false
+}
+
+// legacyIsMasterNode returns true if given node is a registered master according
+// to the logic historically used for this function. This code path is deprecated
+// and the node disruption exclusion label should be used in the future.
+// This code will not be allowed to update to use the node-role label, since
+// node-roles may not be used for feature enablement.
+// DEPRECATED: Will be removed in 1.19
+func legacyIsMasterNode(nodeName string) bool {
+	// We are trying to capture "master(-...)?$" regexp.
+	// However, using regexp.MatchString() results even in more than 35%
+	// of all space allocations in ControllerManager spent in this function.
+	// That's why we are trying to be a bit smarter.
+	if strings.HasSuffix(nodeName, "master") {
+		return true
+	}
+	if len(nodeName) >= 10 {
+		return strings.HasSuffix(nodeName[:len(nodeName)-3], "master-")
+	}
+	return false
+}
+
 // tryUpdateNodeHealth checks a given node's conditions and tries to update it. Returns grace period to
 // which given node is entitled, state of current and last observed Ready Condition, and an error if it occurred.
 func (nc *Controller) tryUpdateNodeHealth(node *v1.Node) (time.Duration, v1.NodeCondition, *v1.NodeCondition, error) {

pkg/controller/nodelifecycle/node_lifecycle_controller_test.go

@@ -23,7 +23,7 @@ import (
 
 	apps "k8s.io/api/apps/v1"
 	coordv1beta1 "k8s.io/api/coordination/v1beta1"
-	"k8s.io/api/core/v1"
+	v1 "k8s.io/api/core/v1"
 	apiequality "k8s.io/apimachinery/pkg/api/equality"
 	"k8s.io/apimachinery/pkg/api/resource"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
@@ -3270,3 +3270,35 @@ func TestTryUpdateNodeHealth(t *testing.T) {
 		})
 	}
 }
+
+func Test_isNodeExcludedFromDisruptionChecks(t *testing.T) {
+	validNodeStatus := v1.NodeStatus{Conditions: []v1.NodeCondition{{Type: "Test"}}}
+	tests := []struct {
+		name string
+
+		enableExclusion bool
+		enableLegacy    bool
+		input           *v1.Node
+		want            bool
+	}{
+		{want: false, input: &v1.Node{Status: validNodeStatus, ObjectMeta: metav1.ObjectMeta{Labels: map[string]string{}}}},
+		{want: false, input: &v1.Node{Status: validNodeStatus, ObjectMeta: metav1.ObjectMeta{Name: "master-abc"}}},
+		{want: false, input: &v1.Node{Status: validNodeStatus, ObjectMeta: metav1.ObjectMeta{Labels: map[string]string{labelNodeDisruptionExclusion: ""}}}},
+
+		{want: false, enableExclusion: true, input: &v1.Node{Status: validNodeStatus, ObjectMeta: metav1.ObjectMeta{Name: "master-abc"}}},
+		{want: false, enableLegacy: true, input: &v1.Node{Status: validNodeStatus, ObjectMeta: metav1.ObjectMeta{Labels: map[string]string{labelNodeDisruptionExclusion: ""}}}},
+
+		{want: true, enableLegacy: true, input: &v1.Node{Status: validNodeStatus, ObjectMeta: metav1.ObjectMeta{Name: "master-abc"}}},
+		{want: true, enableExclusion: true, input: &v1.Node{Status: validNodeStatus, ObjectMeta: metav1.ObjectMeta{Labels: map[string]string{labelNodeDisruptionExclusion: ""}}}},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			defer featuregatetesting.SetFeatureGateDuringTest(t, utilfeature.DefaultFeatureGate, features.NodeDisruptionExclusion, tt.enableExclusion)()
+			defer featuregatetesting.SetFeatureGateDuringTest(t, utilfeature.DefaultFeatureGate, features.LegacyNodeRoleBehavior, tt.enableLegacy)()
+
+			if result := isNodeExcludedFromDisruptionChecks(tt.input); result != tt.want {
+				t.Errorf("isNodeExcludedFromDisruptionChecks() = %v, want %v", result, tt.want)
+			}
+		})
+	}
+}

pkg/features/kube_features.go

@@ -184,6 +184,12 @@ const (
 	// Enable nodes to exclude themselves from service load balancers
 	ServiceNodeExclusion featuregate.Feature = "ServiceNodeExclusion"
 
+	// owner @smarterclayton
+	// alpha: v1.16
+	//
+	// Enable nodes to exclude themselves from network disruption checks
+	NodeDisruptionExclusion featuregate.Feature = "NodeDisruptionExclusion"
+
 	// owner: @jsafrane
 	// alpha: v1.9
 	//
@@ -508,6 +514,7 @@ var defaultKubernetesFeatureGates = map[featuregate.Feature]featuregate.FeatureS
 	CPUCFSQuotaPeriod:                   {Default: false, PreRelease: featuregate.Alpha},
 	TopologyManager:                     {Default: false, PreRelease: featuregate.Alpha},
 	ServiceNodeExclusion:                {Default: false, PreRelease: featuregate.Alpha},
+	NodeDisruptionExclusion:             {Default: false, PreRelease: featuregate.Alpha},
 	MountContainers:                     {Default: false, PreRelease: featuregate.Alpha},
 	CSIDriverRegistry:                   {Default: true, PreRelease: featuregate.Beta},
 	CSINodeInfo:                         {Default: true, PreRelease: featuregate.Beta},