Implement KEP-3836

TL;DR: we want to start failing the LB HC if a node is tainted with ToBeDeletedByClusterAutoscaler.
This field might need refinement, but currently is deemed our best way of understanding if
a node is about to get deleted. We want to do this only for eTP:Cluster services.

The goal is to connection draining terminating nodes

cmd/kube-proxy/app/server.go

@@ -27,6 +27,7 @@ import (
 	"strings"
 	"time"
 
+	"k8s.io/kubernetes/pkg/features"
 	utilnode "k8s.io/kubernetes/pkg/util/node"
 
 	"github.com/fsnotify/fsnotify"
@@ -869,6 +870,11 @@ func (s *ProxyServer) Run() error {
 	if s.Config.DetectLocalMode == kubeproxyconfig.LocalModeNodeCIDR {
 		nodeConfig.RegisterEventHandler(proxy.NewNodePodCIDRHandler(s.podCIDRs))
 	}
+	if utilfeature.DefaultFeatureGate.Enabled(features.KubeProxyDrainingTerminatingNodes) {
+		nodeConfig.RegisterEventHandler(&proxy.NodeEligibleHandler{
+			HealthServer: s.HealthzServer,
+		})
+	}
 	nodeConfig.RegisterEventHandler(s.Proxier)
 
 	go nodeConfig.Run(wait.NeverStop)

pkg/features/kube_features.go

@@ -449,6 +449,14 @@ const (
 	// Add support for distributed tracing in the kubelet
 	KubeletTracing featuregate.Feature = "KubeletTracing"
 
+	// owner: @alexanderConstantinescu
+	// kep: http://kep.k8s.io/3836
+	// alpha: v1.28
+	//
+	// Implement connection draining for terminating nodes for
+	// `externalTrafficPolicy: Cluster` services.
+	KubeProxyDrainingTerminatingNodes featuregate.Feature = "KubeProxyDrainingTerminatingNodes"
+
 	// owner: @zshihang
 	// kep: https://kep.k8s.io/2800
 	// beta: v1.24
@@ -976,6 +984,8 @@ var defaultKubernetesFeatureGates = map[featuregate.Feature]featuregate.FeatureS
 
 	KubeletTracing: {Default: true, PreRelease: featuregate.Beta},
 
+	KubeProxyDrainingTerminatingNodes: {Default: false, PreRelease: featuregate.Alpha},
+
 	LegacyServiceAccountTokenNoAutoGeneration: {Default: true, PreRelease: featuregate.GA, LockToDefault: true}, // remove in 1.29
 
 	LegacyServiceAccountTokenTracking: {Default: true, PreRelease: featuregate.GA, LockToDefault: true}, // remove in 1.30

pkg/proxy/healthcheck/healthcheck_test.go

@@ -27,6 +27,8 @@ import (
 
 	"github.com/google/go-cmp/cmp"
 	"k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+
 	"k8s.io/apimachinery/pkg/types"
 	"k8s.io/apimachinery/pkg/util/dump"
 	"k8s.io/apimachinery/pkg/util/sets"
@@ -131,6 +133,7 @@ type hcPayload struct {
 type healthzPayload struct {
 	LastUpdated string
 	CurrentTime string
+	NodeHealthy bool
 }
 
 type fakeProxierHealthChecker struct {
@@ -427,6 +430,30 @@ func tHandler(hcs *server, nsn types.NamespacedName, status int, endpoints int,
 	}
 }
 
+type nodeTweak func(n *v1.Node)
+
+func makeNode(tweaks ...nodeTweak) *v1.Node {
+	n := &v1.Node{}
+	for _, tw := range tweaks {
+		tw(n)
+	}
+	return n
+}
+
+func tweakDeleted() nodeTweak {
+	return func(n *v1.Node) {
+		n.DeletionTimestamp = &metav1.Time{
+			Time: time.Now(),
+		}
+	}
+}
+
+func tweakTainted(key string) nodeTweak {
+	return func(n *v1.Node) {
+		n.Spec.Taints = append(n.Spec.Taints, v1.Taint{Key: key})
+	}
+}
+
 func TestHealthzServer(t *testing.T) {
 	listener := newFakeListener()
 	httpFactory := newFakeHTTPServerFactory()
@@ -436,30 +463,99 @@ func TestHealthzServer(t *testing.T) {
 	server := hs.httpFactory.New(hs.addr, healthzHandler{hs: hs})
 
 	// Should return 200 "OK" by default.
-	testHealthzHandler(server, http.StatusOK, t)
+	testHTTPHandler(server, healthzURL, http.StatusOK, t)
 
 	// Should return 200 "OK" after first update
 	hs.Updated()
-	testHealthzHandler(server, http.StatusOK, t)
+	testHTTPHandler(server, healthzURL, http.StatusOK, t)
 
 	// Should continue to return 200 "OK" as long as no further updates are queued
 	fakeClock.Step(25 * time.Second)
-	testHealthzHandler(server, http.StatusOK, t)
+	testHTTPHandler(server, healthzURL, http.StatusOK, t)
 
 	// Should return 503 "ServiceUnavailable" if exceed max update-processing time
 	hs.QueuedUpdate()
 	fakeClock.Step(25 * time.Second)
-	testHealthzHandler(server, http.StatusServiceUnavailable, t)
+	testHTTPHandler(server, healthzURL, http.StatusServiceUnavailable, t)
 
 	// Should return 200 "OK" after processing update
 	hs.Updated()
 	fakeClock.Step(5 * time.Second)
-	testHealthzHandler(server, http.StatusOK, t)
+	testHTTPHandler(server, healthzURL, http.StatusOK, t)
+
+	// Should return 200 "OK" if we've synced a node, tainted in any other way
+	hs.SyncNode(makeNode(tweakTainted("other")))
+	testHTTPHandler(server, healthzURL, http.StatusOK, t)
+
+	// Should return 503 "ServiceUnavailable" if we've synced a ToBeDeletedTaint node
+	hs.SyncNode(makeNode(tweakTainted(ToBeDeletedTaint)))
+	testHTTPHandler(server, healthzURL, http.StatusServiceUnavailable, t)
+
+	// Should return 200 "OK" if we've synced a node, tainted in any other way
+	hs.SyncNode(makeNode(tweakTainted("other")))
+	testHTTPHandler(server, healthzURL, http.StatusOK, t)
+
+	// Should return 503 "ServiceUnavailable" if we've synced a deleted node
+	hs.SyncNode(makeNode(tweakDeleted()))
+	testHTTPHandler(server, healthzURL, http.StatusServiceUnavailable, t)
 }
 
-func testHealthzHandler(server httpServer, status int, t *testing.T) {
+func TestLivezServer(t *testing.T) {
+	listener := newFakeListener()
+	httpFactory := newFakeHTTPServerFactory()
+	fakeClock := testingclock.NewFakeClock(time.Now())
+
+	hs := newProxierHealthServer(listener, httpFactory, fakeClock, "127.0.0.1:10256", 10*time.Second, nil, nil)
+	server := hs.httpFactory.New(hs.addr, livezHandler{hs: hs})
+
+	// Should return 200 "OK" by default.
+	testHTTPHandler(server, livezURL, http.StatusOK, t)
+
+	// Should return 200 "OK" after first update
+	hs.Updated()
+	testHTTPHandler(server, livezURL, http.StatusOK, t)
+
+	// Should continue to return 200 "OK" as long as no further updates are queued
+	fakeClock.Step(25 * time.Second)
+	testHTTPHandler(server, livezURL, http.StatusOK, t)
+
+	// Should return 503 "ServiceUnavailable" if exceed max update-processing time
+	hs.QueuedUpdate()
+	fakeClock.Step(25 * time.Second)
+	testHTTPHandler(server, livezURL, http.StatusServiceUnavailable, t)
+
+	// Should return 200 "OK" after processing update
+	hs.Updated()
+	fakeClock.Step(5 * time.Second)
+	testHTTPHandler(server, livezURL, http.StatusOK, t)
+
+	// Should return 200 "OK" irrespective of node syncs
+	hs.SyncNode(makeNode(tweakTainted("other")))
+	testHTTPHandler(server, livezURL, http.StatusOK, t)
+
+	// Should return 200 "OK" irrespective of node syncs
+	hs.SyncNode(makeNode(tweakTainted(ToBeDeletedTaint)))
+	testHTTPHandler(server, livezURL, http.StatusOK, t)
+
+	// Should return 200 "OK" irrespective of node syncs
+	hs.SyncNode(makeNode(tweakTainted("other")))
+	testHTTPHandler(server, livezURL, http.StatusOK, t)
+
+	// Should return 200 "OK" irrespective of node syncs
+	hs.SyncNode(makeNode(tweakDeleted()))
+	testHTTPHandler(server, livezURL, http.StatusOK, t)
+}
+
+type url string
+
+var (
+	healthzURL url = "/healthz"
+	livezURL   url = "/livez"
+)
+
+func testHTTPHandler(server httpServer, u url, status int, t *testing.T) {
 	handler := server.(*fakeHTTPServer).handler
-	req, err := http.NewRequest("GET", "/healthz", nil)
+	req, err := http.NewRequest("GET", string(u), nil)
 	if err != nil {
 		t.Fatal(err)
 	}

pkg/proxy/healthcheck/proxier_health.go

@@ -29,6 +29,12 @@ import (
 	"k8s.io/utils/clock"
 )
 
+const (
+	// ToBeDeletedTaint is a taint used by the CLuster Autoscaler before marking a node for deletion. Defined in
+	// https://github.com/kubernetes/autoscaler/blob/e80ab518340f88f364fe3ef063f8303755125971/cluster-autoscaler/utils/deletetaint/delete.go#L36
+	ToBeDeletedTaint = "ToBeDeletedByClusterAutoscaler"
+)
+
 // ProxierHealthUpdater allows callers to update healthz timestamp only.
 type ProxierHealthUpdater interface {
 	// QueuedUpdate should be called when the proxier receives a Service or Endpoints
@@ -42,6 +48,10 @@ type ProxierHealthUpdater interface {
 	// Run starts the healthz HTTP server and blocks until it exits.
 	Run() error
 
+	// Sync the node and determine if its eligible or not. Eligible is
+	// defined as being: not tainted by ToBeDeletedTaint and not deleted.
+	SyncNode(node *v1.Node)
+
 	proxierHealthChecker
 }
 
@@ -62,6 +72,7 @@ type proxierHealthServer struct {
 
 	lastUpdated         atomic.Value
 	oldestPendingQueued atomic.Value
+	nodeEligible        atomic.Bool
 }
 
 // NewProxierHealthServer returns a proxier health http server.
@@ -70,7 +81,7 @@ func NewProxierHealthServer(addr string, healthTimeout time.Duration, recorder e
 }
 
 func newProxierHealthServer(listener listener, httpServerFactory httpServerFactory, c clock.Clock, addr string, healthTimeout time.Duration, recorder events.EventRecorder, nodeRef *v1.ObjectReference) *proxierHealthServer {
-	return &proxierHealthServer{
+	hs := &proxierHealthServer{
 		listener:      listener,
 		httpFactory:   httpServerFactory,
 		clock:         c,
@@ -79,6 +90,11 @@ func newProxierHealthServer(listener listener, httpServerFactory httpServerFacto
 		recorder:      recorder,
 		nodeRef:       nodeRef,
 	}
+	// The node is eligible (and thus the proxy healthy) while it's starting up
+	// and until we've processed the first node event that indicates the
+	// contrary.
+	hs.nodeEligible.Store(true)
+	return hs
 }
 
 // Updated indicates that kube-proxy has successfully updated its backend, so it should
@@ -96,8 +112,8 @@ func (hs *proxierHealthServer) QueuedUpdate() {
 	hs.oldestPendingQueued.CompareAndSwap(zeroTime, hs.clock.Now())
 }
 
-// IsHealthy returns the proxier's health state, following the same definition
-// the HTTP server defines.
+// IsHealthy returns only the proxier's health state, following the same
+// definition the HTTP server defines, but ignoring the state of the Node.
 func (hs *proxierHealthServer) IsHealthy() bool {
 	isHealthy, _, _ := hs.isHealthy()
 	return isHealthy
@@ -123,14 +139,28 @@ func (hs *proxierHealthServer) isHealthy() (bool, time.Time, time.Time) {
 		// There's an unprocessed update queued, but it's not late yet
 		healthy = true
 	}
-
 	return healthy, lastUpdated, currentTime
 }
 
+func (hs *proxierHealthServer) SyncNode(node *v1.Node) {
+	if !node.DeletionTimestamp.IsZero() {
+		hs.nodeEligible.Store(false)
+		return
+	}
+	for _, taint := range node.Spec.Taints {
+		if taint.Key == ToBeDeletedTaint {
+			hs.nodeEligible.Store(false)
+			return
+		}
+	}
+	hs.nodeEligible.Store(true)
+}
+
 // Run starts the healthz HTTP server and blocks until it exits.
 func (hs *proxierHealthServer) Run() error {
 	serveMux := http.NewServeMux()
 	serveMux.Handle("/healthz", healthzHandler{hs: hs})
+	serveMux.Handle("/livez", livezHandler{hs: hs})
 	server := hs.httpFactory.New(hs.addr, serveMux)
 
 	listener, err := hs.listener.Listen(hs.addr)
@@ -156,6 +186,30 @@ type healthzHandler struct {
 }
 
 func (h healthzHandler) ServeHTTP(resp http.ResponseWriter, req *http.Request) {
+	nodeEligible := h.hs.nodeEligible.Load()
+	healthy, lastUpdated, currentTime := h.hs.isHealthy()
+	healthy = healthy && nodeEligible
+	resp.Header().Set("Content-Type", "application/json")
+	resp.Header().Set("X-Content-Type-Options", "nosniff")
+	if !healthy {
+		resp.WriteHeader(http.StatusServiceUnavailable)
+	} else {
+		resp.WriteHeader(http.StatusOK)
+		// In older releases, the returned "lastUpdated" time indicated the last
+		// time the proxier sync loop ran, even if nothing had changed. To
+		// preserve compatibility, we use the same semantics: the returned
+		// lastUpdated value is "recent" if the server is healthy. The kube-proxy
+		// metrics provide more detailed information.
+		lastUpdated = currentTime
+	}
+	fmt.Fprintf(resp, `{"lastUpdated": %q,"currentTime": %q, "nodeEligible": %v}`, lastUpdated, currentTime, nodeEligible)
+}
+
+type livezHandler struct {
+	hs *proxierHealthServer
+}
+
+func (h livezHandler) ServeHTTP(resp http.ResponseWriter, req *http.Request) {
 	healthy, lastUpdated, currentTime := h.hs.isHealthy()
 	resp.Header().Set("Content-Type", "application/json")
 	resp.Header().Set("X-Content-Type-Options", "nosniff")

pkg/proxy/iptables/proxier.go

@@ -652,6 +652,7 @@ func (proxier *Proxier) OnNodeDelete(node *v1.Node) {
 			"eventNode", node.Name, "currentNode", proxier.hostname)
 		return
 	}
+
 	proxier.mu.Lock()
 	proxier.nodeLabels = nil
 	proxier.needFullSync = true

pkg/proxy/ipvs/proxier.go

@@ -902,6 +902,7 @@ func (proxier *Proxier) OnNodeDelete(node *v1.Node) {
 		klog.ErrorS(nil, "Received a watch event for a node that doesn't match the current node", "eventNode", node.Name, "currentNode", proxier.hostname)
 		return
 	}
+
 	proxier.mu.Lock()
 	proxier.nodeLabels = nil
 	proxier.mu.Unlock()

pkg/proxy/node.go

@@ -23,6 +23,7 @@ import (
 	v1 "k8s.io/api/core/v1"
 	"k8s.io/klog/v2"
 	"k8s.io/kubernetes/pkg/proxy/config"
+	"k8s.io/kubernetes/pkg/proxy/healthcheck"
 )
 
 // NodePodCIDRHandler handles the life cycle of kube-proxy based on the node PodCIDR assigned
@@ -85,3 +86,23 @@ func (n *NodePodCIDRHandler) OnNodeDelete(node *v1.Node) {
 
 // OnNodeSynced is a handler for Node syncs.
 func (n *NodePodCIDRHandler) OnNodeSynced() {}
+
+// NodeEligibleHandler handles the life cycle of the Node's eligibility, as
+// determined by the health server for directing load balancer traffic.
+type NodeEligibleHandler struct {
+	HealthServer healthcheck.ProxierHealthUpdater
+}
+
+var _ config.NodeHandler = &NodeEligibleHandler{}
+
+// OnNodeAdd is a handler for Node creates.
+func (n *NodeEligibleHandler) OnNodeAdd(node *v1.Node) { n.HealthServer.SyncNode(node) }
+
+// OnNodeUpdate is a handler for Node updates.
+func (n *NodeEligibleHandler) OnNodeUpdate(_, node *v1.Node) { n.HealthServer.SyncNode(node) }
+
+// OnNodeDelete is a handler for Node deletes.
+func (n *NodeEligibleHandler) OnNodeDelete(node *v1.Node) { n.HealthServer.SyncNode(node) }
+
+// OnNodeSynced is a handler for Node syncs.
+func (n *NodeEligibleHandler) OnNodeSynced() {}