Reinitialize ARP/NDP responders when the transport interface changes

cmd/antrea-agent/agent.go

@@ -52,6 +52,7 @@ import (
 	"antrea.io/antrea/pkg/agent/flowexporter"
 	"antrea.io/antrea/pkg/agent/flowexporter/exporter"
 	"antrea.io/antrea/pkg/agent/interfacestore"
+	"antrea.io/antrea/pkg/agent/ipassigner/linkmonitor"
 	"antrea.io/antrea/pkg/agent/memberlist"
 	"antrea.io/antrea/pkg/agent/metrics"
 	"antrea.io/antrea/pkg/agent/monitortool"
@@ -546,6 +547,7 @@ func run(o *Options) error {
 	var externalIPPoolController *externalippool.ExternalIPPoolController
 	var externalIPController *serviceexternalip.ServiceExternalIPController
 	var memberlistCluster *memberlist.Cluster
+	var linkMonitor linkmonitor.Interface
 
 	if o.enableEgress || features.DefaultFeatureGate.Enabled(features.ServiceExternalIP) {
 		externalIPPoolController = externalippool.NewExternalIPPoolController(
@@ -565,13 +567,15 @@ func run(o *Options) error {
 		if err != nil {
 			return fmt.Errorf("error creating new memberlist cluster: %v", err)
 		}
+		linkMonitor = linkmonitor.NewLinkMonitor()
 	}
 	if o.enableEgress {
 		egressController, err = egress.NewEgressController(
 			ofClient, k8sClient, antreaClientProvider, crdClient, ifaceStore, routeClient, nodeConfig.Name, nodeConfig.NodeTransportInterfaceName,
 			memberlistCluster, egressInformer, externalIPPoolInformer, nodeInformer, podUpdateChannel, serviceCIDRProvider, o.config.Egress.MaxEgressIPsPerNode,
 			features.DefaultFeatureGate.Enabled(features.EgressTrafficShaping),
 			features.DefaultFeatureGate.Enabled(features.EgressSeparateSubnet),
+			linkMonitor,
 		)
 		if err != nil {
 			return fmt.Errorf("error creating new Egress controller: %v", err)
@@ -584,12 +588,17 @@ func run(o *Options) error {
 			memberlistCluster,
 			serviceInformer,
 			endpointsInformer,
+			linkMonitor,
 		)
 		if err != nil {
 			return fmt.Errorf("error creating new ServiceExternalIP controller: %v", err)
 		}
 	}
 
+	if linkMonitor != nil {
+		go linkMonitor.Run(stopCh)
+	}
+
 	var cniServer *cniserver.CNIServer
 	var externalNodeController *externalnode.ExternalNodeController
 	var localExternalNodeInformer cache.SharedIndexInformer

go.mod

@@ -35,7 +35,7 @@ require (
 	github.com/lithammer/dedent v1.1.0
 	github.com/mdlayher/arp v0.0.0-20220221190821-c37aaafac7f9
 	github.com/mdlayher/ethernet v0.0.0-20220221185849-529eae5b6118
-	github.com/mdlayher/ndp v0.8.0
+	github.com/mdlayher/ndp v1.1.0
 	github.com/mdlayher/packet v1.1.2
 	github.com/miekg/dns v1.1.62
 	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822
@@ -214,7 +214,6 @@ require (
 	github.com/vishvananda/netns v0.0.4 // indirect
 	github.com/x448/float16 v0.8.4 // indirect
 	github.com/xlab/treeprint v1.2.0 // indirect
-	gitlab.com/golang-commonmark/puny v0.0.0-20191124015043-9f83538fa04f // indirect
 	go.etcd.io/etcd/api/v3 v3.5.14 // indirect
 	go.etcd.io/etcd/client/pkg/v3 v3.5.14 // indirect
 	go.etcd.io/etcd/client/v3 v3.5.14 // indirect
@@ -251,3 +250,6 @@ require (
 	sigs.k8s.io/kustomize/kyaml v0.17.1 // indirect
 	sigs.k8s.io/structured-merge-diff/v4 v4.4.1 // indirect
 )
+
+// remove this when https://github.com/mdlayher/ndp/pull/32 gets merged
+replace github.com/mdlayher/ndp => github.com/antrea-io/ndp v0.0.0-20241107040829-6f35f2e50f4c

go.sum

@@ -59,6 +59,8 @@ github.com/andybalholm/brotli v1.0.4 h1:V7DdXeJtZscaqfNuAdSRuRFzuiKlHSC/Zh3zl9qY
 github.com/andybalholm/brotli v1.0.4/go.mod h1:fO7iG3H7G2nSZ7m0zPUDn85XEX2GTukHGRSepvi9Eig=
 github.com/antlr4-go/antlr/v4 v4.13.0 h1:lxCg3LAv+EUK6t1i0y1V6/SLeUi0eKEKdhQAlS8TVTI=
 github.com/antlr4-go/antlr/v4 v4.13.0/go.mod h1:pfChB/xh/Unjila75QW7+VU4TSnWnnk9UTnmpPaOR2g=
+github.com/antrea-io/ndp v0.0.0-20241107040829-6f35f2e50f4c h1:9BpiAOFYkjvKFzSCoQHRcOFmXBHpgq74wpSu0CkM6F8=
+github.com/antrea-io/ndp v0.0.0-20241107040829-6f35f2e50f4c/go.mod h1:FmgESgemgjl38vuOIyAHWUUL6vQKA/pQNkvXdWsdQFM=
 github.com/armon/consul-api v0.0.0-20180202201655-eb2c6b5be1b6/go.mod h1:grANhF5doyWs3UAsr3K4I6qtAmlQcZDesFNEHPZAzj8=
 github.com/armon/go-metrics v0.4.0 h1:yCQqn7dwca4ITXb+CbubHmedzaQYHhNhrEXLYUeEe8Q=
 github.com/armon/go-metrics v0.4.0/go.mod h1:E6amYzXo6aW1tqzoZGT755KkbgrJsSdpwZ+3JqfkOG4=
@@ -349,7 +351,6 @@ github.com/google/go-cmp v0.2.0/go.mod h1:oXzfMopK8JAjlY9xF4vHSVASa0yLyX7SntLO5a
 github.com/google/go-cmp v0.3.0/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=
 github.com/google/go-cmp v0.3.1/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=
 github.com/google/go-cmp v0.4.0/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
-github.com/google/go-cmp v0.4.1/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
 github.com/google/go-cmp v0.5.0/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
 github.com/google/go-cmp v0.5.1/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
 github.com/google/go-cmp v0.5.2/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
@@ -529,8 +530,6 @@ github.com/mdlayher/ethernet v0.0.0-20220221185849-529eae5b6118/go.mod h1:ZFUnHI
 github.com/mdlayher/ethtool v0.0.0-20210210192532-2b88debcdd43/go.mod h1:+t7E0lkKfbBsebllff1xdTmyJt8lH37niI6kwFk9OTo=
 github.com/mdlayher/genetlink v1.0.0 h1:OoHN1OdyEIkScEmRgxLEe2M9U8ClMytqA5niynLtfj0=
 github.com/mdlayher/genetlink v1.0.0/go.mod h1:0rJ0h4itni50A86M2kHcgS85ttZazNt7a8H2a2cw0Gc=
-github.com/mdlayher/ndp v0.8.0 h1:oVCl5JZSzT/YJE6cJd7EnNDWmX1fl4hJV0S/UCBNoHE=
-github.com/mdlayher/ndp v0.8.0/go.mod h1:32w/5dDZWVSEOxyniAgKK4d7dHTuO6TCxWmUznQe3f8=
 github.com/mdlayher/netlink v0.0.0-20190409211403-11939a169225/go.mod h1:eQB3mZE4aiYnlUsyGGCOpPETfdQq4Jhsgf1fk3cwQaA=
 github.com/mdlayher/netlink v1.0.0/go.mod h1:KxeJAFOFLG6AjpyDkQ/iIhxygIUKD+vcwqcnu43w/+M=
 github.com/mdlayher/netlink v1.1.0/go.mod h1:H4WCitaheIsdF9yOYu8CFmCgQthAPIWZmcKp9uZHgmY=
@@ -772,8 +771,6 @@ github.com/xordataexchange/crypt v0.0.3-0.20170626215501-b2862e3d0a77/go.mod h1:
 github.com/yuin/goldmark v1.1.27/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
 github.com/yuin/goldmark v1.2.1/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
 github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
-gitlab.com/golang-commonmark/puny v0.0.0-20191124015043-9f83538fa04f h1:Wku8eEdeJqIOFHtrfkYUByc4bCaTeA6fL0UJgfEiFMI=
-gitlab.com/golang-commonmark/puny v0.0.0-20191124015043-9f83538fa04f/go.mod h1:Tiuhl+njh/JIg0uS/sOJVYi0x2HEa5rc1OAaVsb5tAs=
 go.etcd.io/bbolt v1.3.2/go.mod h1:IbVyRI1SCnLcuJnV2u8VeU0CEYM7e686BmAb1XKL+uU=
 go.etcd.io/bbolt v1.3.3/go.mod h1:IbVyRI1SCnLcuJnV2u8VeU0CEYM7e686BmAb1XKL+uU=
 go.etcd.io/bbolt v1.3.9 h1:8x7aARPEXiXbHmtUwAIv7eV2fQFHrLLavdiJ3uzJXoI=
@@ -888,7 +885,6 @@ golang.org/x/net v0.0.0-20191007182048-72f939374954/go.mod h1:z5CRVTTTmAJ677TzLL
 golang.org/x/net v0.0.0-20200202094626-16171245cfb2/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
 golang.org/x/net v0.0.0-20200226121028-0de0cce0169b/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
 golang.org/x/net v0.0.0-20200520004742-59133d7f0dd7/go.mod h1:qpuaurCH72eLCgpAm/N6yyVIVM9cpaDIP3A8BGJEC5A=
-golang.org/x/net v0.0.0-20200602114024-627f9648deb9/go.mod h1:qpuaurCH72eLCgpAm/N6yyVIVM9cpaDIP3A8BGJEC5A=
 golang.org/x/net v0.0.0-20201010224723-4f7140c49acb/go.mod h1:sp8m0HH+o8qH0wwXwYZr8TS3Oi6o0r6Gce1SSxlDquU=
 golang.org/x/net v0.0.0-20201021035429-f5854403a974/go.mod h1:sp8m0HH+o8qH0wwXwYZr8TS3Oi6o0r6Gce1SSxlDquU=
 golang.org/x/net v0.0.0-20201110031124-69a78807bb2b/go.mod h1:sp8m0HH+o8qH0wwXwYZr8TS3Oi6o0r6Gce1SSxlDquU=
@@ -916,7 +912,6 @@ golang.org/x/sync v0.0.0-20181221193216-37e7f081c4d4/go.mod h1:RxMgew5VJxzue5/jJ
 golang.org/x/sync v0.0.0-20190227155943-e225da77a7e6/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
-golang.org/x/sync v0.0.0-20200317015054-43a5402ce75a/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20201020160332-67f06af15bc9/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20210220032951-036812b2e83c/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20220722155255-886fb9371eb4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
@@ -953,7 +948,6 @@ golang.org/x/sys v0.0.0-20200202164722-d101bd2416d5/go.mod h1:h1NjWce9XRLGQEsW7w
 golang.org/x/sys v0.0.0-20200217220822-9197077df867/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20200323222414-85ca7c5b95cd/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20200519105757-fe76b779f299/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.0.0-20200602100848-8d3cce7afc34/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20200728102440-3e129f6d46b1/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20200930185726-fdedc70b468f/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20201009025420-dfb3f7c4e634/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=

pkg/agent/controller/egress/egress_controller.go

@@ -44,6 +44,7 @@ import (
 	"antrea.io/antrea/pkg/agent/client"
 	"antrea.io/antrea/pkg/agent/interfacestore"
 	"antrea.io/antrea/pkg/agent/ipassigner"
+	"antrea.io/antrea/pkg/agent/ipassigner/linkmonitor"
 	"antrea.io/antrea/pkg/agent/memberlist"
 	"antrea.io/antrea/pkg/agent/openflow"
 	"antrea.io/antrea/pkg/agent/route"
@@ -205,6 +206,8 @@ type EgressController struct {
 	tableAllocator *idAllocator
 	// Each subnet has its own route table.
 	egressRouteTables map[crdv1b1.SubnetInfo]*egressRouteTable
+
+	linkMonitor linkmonitor.Interface
 }
 
 func NewEgressController(
@@ -225,6 +228,7 @@ func NewEgressController(
 	maxEgressIPsPerNode int,
 	trafficShapingEnabled bool,
 	supportSeparateSubnet bool,
+	linkMonitor linkmonitor.Interface,
 ) (*EgressController, error) {
 	if trafficShapingEnabled && !openflow.OVSMetersAreSupported() {
 		klog.Info("EgressTrafficShaping feature gate is enabled, but it is ignored because OVS meters are not supported.")
@@ -273,6 +277,7 @@ func NewEgressController(
 		externalIPPoolLister:       externalIPPoolInformer.Lister(),
 		externalIPPoolListerSynced: externalIPPoolInformer.Informer().HasSynced,
 		supportSeparateSubnet:      supportSeparateSubnet,
+		linkMonitor:                linkMonitor,
 	}
 	if supportSeparateSubnet {
 		c.egressRouteTables = map[crdv1b1.SubnetInfo]*egressRouteTable{}
@@ -285,7 +290,7 @@ func NewEgressController(
 			resyncPeriod,
 		)
 	}
-	ipAssigner, err := newIPAssigner(nodeTransportInterface, egressDummyDevice)
+	ipAssigner, err := newIPAssigner(nodeTransportInterface, egressDummyDevice, linkMonitor)
 	if err != nil {
 		return nil, fmt.Errorf("initializing egressIP assigner failed: %v", err)
 	}
@@ -505,7 +510,7 @@ func (c *EgressController) Run(stopCh <-chan struct{}) {
 	go c.localIPDetector.Run(stopCh)
 	go c.egressIPScheduler.Run(stopCh)
 	go c.ipAssigner.Run(stopCh)
-	if !cache.WaitForNamedCacheSync(controllerName, stopCh, c.egressListerSynced, c.externalIPPoolListerSynced, c.localIPDetector.HasSynced, c.egressIPScheduler.HasScheduled) {
+	if !cache.WaitForNamedCacheSync(controllerName, stopCh, c.egressListerSynced, c.externalIPPoolListerSynced, c.localIPDetector.HasSynced, c.egressIPScheduler.HasScheduled, c.linkMonitor.HasSynced) {
 		return
 	}
 

pkg/agent/controller/egress/egress_controller_test.go

@@ -38,6 +38,7 @@ import (
 
 	"antrea.io/antrea/pkg/agent/interfacestore"
 	"antrea.io/antrea/pkg/agent/ipassigner"
+	"antrea.io/antrea/pkg/agent/ipassigner/linkmonitor"
 	ipassignertest "antrea.io/antrea/pkg/agent/ipassigner/testing"
 	"antrea.io/antrea/pkg/agent/memberlist"
 	openflowtest "antrea.io/antrea/pkg/agent/openflow/testing"
@@ -137,7 +138,7 @@ func (c *fakeSingleNodeCluster) AddClusterEventHandler(handler memberlist.Cluste
 
 func mockNewIPAssigner(ipAssigner ipassigner.IPAssigner) func() {
 	originalNewIPAssigner := newIPAssigner
-	newIPAssigner = func(_, _ string) (ipassigner.IPAssigner, error) {
+	newIPAssigner = func(_, _ string, _ linkmonitor.Interface) (ipassigner.IPAssigner, error) {
 		return ipAssigner, nil
 	}
 	return func() {
@@ -203,6 +204,7 @@ func newFakeController(t *testing.T, initObjects []runtime.Object) *fakeControll
 		255,
 		true,
 		true,
+		nil,
 	)
 	egressController.localIPDetector = localIPDetector
 	return &fakeController{

pkg/agent/controller/serviceexternalip/controller.go

@@ -32,6 +32,7 @@ import (
 
 	"antrea.io/antrea/pkg/agent/apis"
 	"antrea.io/antrea/pkg/agent/ipassigner"
+	"antrea.io/antrea/pkg/agent/ipassigner/linkmonitor"
 	"antrea.io/antrea/pkg/agent/memberlist"
 	"antrea.io/antrea/pkg/agent/types"
 	"antrea.io/antrea/pkg/querier"
@@ -77,6 +78,8 @@ type ServiceExternalIPController struct {
 
 	assignedIPs      map[string]sets.Set[string]
 	assignedIPsMutex sync.Mutex
+
+	linkMonitor linkmonitor.Interface
 }
 
 var _ querier.ServiceExternalIPStatusQuerier = (*ServiceExternalIPController)(nil)
@@ -87,6 +90,7 @@ func NewServiceExternalIPController(
 	cluster memberlist.Interface,
 	serviceInformer coreinformers.ServiceInformer,
 	endpointsInformer coreinformers.EndpointsInformer,
+	linkMonitor linkmonitor.Interface,
 ) (*ServiceExternalIPController, error) {
 	c := &ServiceExternalIPController{
 		nodeName: nodeName,
@@ -105,8 +109,9 @@ func NewServiceExternalIPController(
 		endpointsListerSynced: endpointsInformer.Informer().HasSynced,
 		externalIPStates:      make(map[apimachinerytypes.NamespacedName]externalIPState),
 		assignedIPs:           make(map[string]sets.Set[string]),
+		linkMonitor:           linkMonitor,
 	}
-	ipAssigner, err := ipassigner.NewIPAssigner(nodeTransportInterface, "")
+	ipAssigner, err := ipassigner.NewIPAssigner(nodeTransportInterface, "", linkMonitor)
 	if err != nil {
 		return nil, fmt.Errorf("initializing service external IP assigner failed: %v", err)
 	}
@@ -240,7 +245,7 @@ func (c *ServiceExternalIPController) Run(stopCh <-chan struct{}) {
 	klog.Infof("Starting %s", controllerName)
 	defer klog.Infof("Shutting down %s", controllerName)
 
-	if !cache.WaitForNamedCacheSync(controllerName, stopCh, c.serviceListerSynced, c.endpointsListerSynced) {
+	if !cache.WaitForNamedCacheSync(controllerName, stopCh, c.serviceListerSynced, c.endpointsListerSynced, c.linkMonitor.HasSynced) {
 		return
 	}
 

pkg/agent/ipassigner/ip_assigner_linux.go

@@ -27,6 +27,7 @@ import (
 	"k8s.io/klog/v2"
 	utilnet "k8s.io/utils/net"
 
+	"antrea.io/antrea/pkg/agent/ipassigner/linkmonitor"
 	"antrea.io/antrea/pkg/agent/ipassigner/responder"
 	"antrea.io/antrea/pkg/agent/util"
 	"antrea.io/antrea/pkg/agent/util/arping"
@@ -217,7 +218,7 @@ type ipAssigner struct {
 }
 
 // NewIPAssigner returns an *ipAssigner.
-func NewIPAssigner(nodeTransportInterface string, dummyDeviceName string) (IPAssigner, error) {
+func NewIPAssigner(nodeTransportInterface string, dummyDeviceName string, linkMonitor linkmonitor.Interface) (IPAssigner, error) {
 	ipv4, ipv6, externalInterface, err := util.GetIPNetDeviceByName(nodeTransportInterface)
 	if err != nil {
 		return nil, fmt.Errorf("get IPNetDevice from name %s error: %+v", nodeTransportInterface, err)
@@ -242,17 +243,11 @@ func NewIPAssigner(nodeTransportInterface string, dummyDeviceName string) (IPAss
 			return nil, err
 		}
 		if dummyDeviceName == "" || arpIgnore > 0 {
-			a.defaultAssignee.arpResponder, err = responder.NewARPResponder(externalInterface)
-			if err != nil {
-				return nil, fmt.Errorf("failed to create ARP responder for link %s: %v", externalInterface.Name, err)
-			}
+			a.defaultAssignee.arpResponder = responder.NewARPResponder(externalInterface.Name, linkMonitor)
 		}
 	}
 	if ipv6 != nil {
-		a.defaultAssignee.ndpResponder, err = responder.NewNDPResponder(externalInterface)
-		if err != nil {
-			return nil, fmt.Errorf("failed to create NDP responder for link %s: %v", externalInterface.Name, err)
-		}
+		a.defaultAssignee.ndpResponder = responder.NewNDPResponder(externalInterface.Name, linkMonitor)
 	}
 	if dummyDeviceName != "" {
 		a.defaultAssignee.link, err = ensureDummyDevice(dummyDeviceName)

pkg/agent/ipassigner/ip_assigner_windows.go

@@ -14,8 +14,12 @@
 
 package ipassigner
 
-import "errors"
+import (
+	"errors"
 
-func NewIPAssigner(nodeTransportInterface string, dummyDeviceName string) (IPAssigner, error) {
+	"antrea.io/antrea/pkg/agent/ipassigner/linkmonitor"
+)
+
+func NewIPAssigner(nodeTransportInterface string, dummyDeviceName string, linkMonitor linkmonitor.Interface) (IPAssigner, error) {
 	return nil, errors.New("IPAssigner is not implemented on Windows")
 }

pkg/agent/ipassigner/linkmonitor/link_monitor.go

@@ -0,0 +1,31 @@
+// Copyright 2024 Antrea Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package linkmonitor
+
+type LinkEventHandler func(linkName string)
+
+type Interface interface {
+	LinkExists(linkName string) bool
+
+	// Run starts the detector.
+	Run(stopCh <-chan struct{})
+
+	// AddEventHandler registers an eventHandler of link updates. It's not thread-safe and should be called before
+	// starting the detector. If no link name is provided, the handler will be called for all link updates.
+	AddEventHandler(handler LinkEventHandler, linkNames ...string)
+
+	// HasSynced returns true if the cache has been initialized with the existing links.
+	HasSynced() bool
+}