cmd/k8s-operator,cmd/containerboot: add kube egress proxy (#9031)

First part of work for the functionality that allows users to create an egress
proxy to access Tailnet services from within Kubernetes cluster workloads.
This PR allows creating an egress proxy that can access Tailscale services over HTTP only.

Updates tailscale/tailscale#8184

Signed-off-by: irbekrm <irbekrm@gmail.com>
Co-authored-by: Maisem Ali <maisem@tailscale.com>
Co-authored-by: Rhea Ghosh <rhea@tailscale.com>

cmd/containerboot/main.go

@@ -16,6 +16,8 @@
 //   - TS_ROUTES: subnet routes to advertise.
 //   - TS_DEST_IP: proxy all incoming Tailscale traffic to the given
 //     destination.
+//   - TS_TAILNET_TARGET_IP: proxy all incoming non-Tailscale traffic to the given
+//     destination.
 //   - TS_TAILSCALED_EXTRA_ARGS: extra arguments to 'tailscaled'.
 //   - TS_EXTRA_ARGS: extra arguments to 'tailscale login', these are not
 //     reset on restart.
@@ -88,8 +90,9 @@ func main() {
 		AuthKey:         defaultEnvs([]string{"TS_AUTHKEY", "TS_AUTH_KEY"}, ""),
 		Hostname:        defaultEnv("TS_HOSTNAME", ""),
 		Routes:          defaultEnv("TS_ROUTES", ""),
-		ProxyTo:         defaultEnv("TS_DEST_IP", ""),
 		ServeConfigPath: defaultEnv("TS_SERVE_CONFIG", ""),
+		ProxyTo:         defaultEnv("TS_DEST_IP", ""),
+		TailnetTargetIP: defaultEnv("TS_TAILNET_TARGET_IP", ""),
 		DaemonExtraArgs: defaultEnv("TS_TAILSCALED_EXTRA_ARGS", ""),
 		ExtraArgs:       defaultEnv("TS_EXTRA_ARGS", ""),
 		InKubernetes:    os.Getenv("KUBERNETES_SERVICE_HOST") != "",
@@ -107,16 +110,17 @@ func main() {
 	if cfg.ProxyTo != "" && cfg.UserspaceMode {
 		log.Fatal("TS_DEST_IP is not supported with TS_USERSPACE")
 	}
-	if cfg.ProxyTo != "" && cfg.ServeConfigPath != "" {
+
-		log.Fatal("TS_DEST_IP is not supported with TS_SERVE_CONFIG")
+	if cfg.TailnetTargetIP != "" && cfg.UserspaceMode {
+		log.Fatal("TS_TAILNET_TARGET_IP is not supported with TS_USERSPACE")
 	}
 
 	if !cfg.UserspaceMode {
 		if err := ensureTunFile(cfg.Root); err != nil {
 			log.Fatalf("Unable to create tuntap device file: %v", err)
 		}
-		if cfg.ProxyTo != "" || cfg.Routes != "" {
+		if cfg.ProxyTo != "" || cfg.Routes != "" || cfg.TailnetTargetIP != "" {
-			if err := ensureIPForwarding(cfg.Root, cfg.ProxyTo, cfg.Routes); err != nil {
+			if err := ensureIPForwarding(cfg.Root, cfg.ProxyTo, cfg.TailnetTargetIP, cfg.Routes); err != nil {
 				log.Printf("Failed to enable IP forwarding: %v", err)
 				log.Printf("To run tailscale as a proxy or router container, IP forwarding must be enabled.")
 				if cfg.InKubernetes {
@@ -270,7 +274,7 @@ authLoop:
 	}
 
 	var (
-		wantProxy         = cfg.ProxyTo != ""
+		wantProxy         = cfg.ProxyTo != "" || cfg.TailnetTargetIP != ""
 		wantDeviceInfo    = cfg.InKubernetes && cfg.KubeSecret != "" && cfg.KubernetesCanPatch
 		startupTasksDone  = false
 		currentIPs        deephash.Sum // tailscale IPs assigned to device
@@ -298,10 +302,12 @@ authLoop:
 		}
 		if n.NetMap != nil {
 			addrs := n.NetMap.SelfNode.Addresses().AsSlice()
-			if cfg.ProxyTo != "" && len(addrs) > 0 && deephash.Update(&currentIPs, &addrs) {
+			newCurrentIPs := deephash.Hash(&addrs)
+			ipsHaveChanged := newCurrentIPs != currentIPs
+			if cfg.ProxyTo != "" && len(addrs) > 0 && ipsHaveChanged {
 				log.Printf("Installing proxy rules")
-				if err := installIPTablesRule(ctx, cfg.ProxyTo, addrs); err != nil {
+				if err := installIngressForwardingRule(ctx, cfg.ProxyTo, addrs); err != nil {
-					log.Fatalf("installing proxy rules: %v", err)
+					log.Fatalf("installing ingress proxy rules: %v", err)
 				}
 			}
 			if cfg.ServeConfigPath != "" && len(n.NetMap.DNS.CertDomains) > 0 {
@@ -314,6 +320,13 @@ authLoop:
 					}
 				}
 			}
+			if cfg.TailnetTargetIP != "" && ipsHaveChanged && len(addrs) > 0 {
+				if err := installEgressForwardingRule(ctx, cfg.TailnetTargetIP, addrs); err != nil {
+					log.Fatalf("installing egress proxy rules: %v", err)
+				}
+			}
+			currentIPs = newCurrentIPs
+
 			deviceInfo := []any{n.NetMap.SelfNode.StableID(), n.NetMap.SelfNode.Name()}
 			if cfg.InKubernetes && cfg.KubernetesCanPatch && cfg.KubeSecret != "" && deephash.Update(&currentDeviceInfo, &deviceInfo) {
 				if err := storeDeviceInfo(ctx, cfg.KubeSecret, n.NetMap.SelfNode.StableID(), n.NetMap.SelfNode.Name(), n.NetMap.SelfNode.Addresses().AsSlice()); err != nil {
@@ -572,14 +585,25 @@ func ensureTunFile(root string) error {
 }
 
 // ensureIPForwarding enables IPv4/IPv6 forwarding for the container.
-func ensureIPForwarding(root, proxyTo, routes string) error {
+func ensureIPForwarding(root, clusterProxyTarget, tailnetTargetiP, routes string) error {
 	var (
 		v4Forwarding, v6Forwarding bool
 	)
-	if proxyTo != "" {
+	if clusterProxyTarget != "" {
-		proxyIP, err := netip.ParseAddr(proxyTo)
+		proxyIP, err := netip.ParseAddr(clusterProxyTarget)
 		if err != nil {
-			return fmt.Errorf("invalid proxy destination IP: %v", err)
+			return fmt.Errorf("invalid cluster destination IP: %v", err)
+		}
+		if proxyIP.Is4() {
+			v4Forwarding = true
+		} else {
+			v6Forwarding = true
+		}
+	}
+	if tailnetTargetiP != "" {
+		proxyIP, err := netip.ParseAddr(tailnetTargetiP)
+		if err != nil {
+			return fmt.Errorf("invalid tailnet destination IP: %v", err)
 		}
 		if proxyIP.Is4() {
 			v4Forwarding = true
@@ -629,7 +653,53 @@ func ensureIPForwarding(root, proxyTo, routes string) error {
 	return nil
 }
 
-func installIPTablesRule(ctx context.Context, dstStr string, tsIPs []netip.Prefix) error {
+func installEgressForwardingRule(ctx context.Context, dstStr string, tsIPs []netip.Prefix) error {
+	dst, err := netip.ParseAddr(dstStr)
+	if err != nil {
+		return err
+	}
+	argv0 := "iptables"
+	if dst.Is6() {
+		argv0 = "ip6tables"
+	}
+	var local string
+	for _, pfx := range tsIPs {
+		if !pfx.IsSingleIP() {
+			continue
+		}
+		if pfx.Addr().Is4() != dst.Is4() {
+			continue
+		}
+		local = pfx.Addr().String()
+		break
+	}
+	if local == "" {
+		return fmt.Errorf("no tailscale IP matching family of %s found in %v", dstStr, tsIPs)
+	}
+	// Technically, if the control server ever changes the IPs assigned to this
+	// node, we'll slowly accumulate iptables rules. This shouldn't happen, so
+	// for now we'll live with it.
+	// Set up a rule that ensures that all packets
+	// except for those received on tailscale0 interface is forwarded to
+	// destination address
+	cmdDNAT := exec.CommandContext(ctx, argv0, "-t", "nat", "-I", "PREROUTING", "1", "!", "-i", "tailscale0", "-j", "DNAT", "--to-destination", dstStr)
+	cmdDNAT.Stdout = os.Stdout
+	cmdDNAT.Stderr = os.Stderr
+	if err := cmdDNAT.Run(); err != nil {
+		return fmt.Errorf("executing iptables failed: %w", err)
+	}
+	// Set up a rule that ensures that all packets sent to the destination
+	// address will have the proxy's IP set as source IP
+	cmdSNAT := exec.CommandContext(ctx, argv0, "-t", "nat", "-I", "POSTROUTING", "1", "--destination", dstStr, "-j", "SNAT", "--to-source", local)
+	cmdSNAT.Stdout = os.Stdout
+	cmdSNAT.Stderr = os.Stderr
+	if err := cmdSNAT.Run(); err != nil {
+		return fmt.Errorf("setting up SNAT via iptables failed: %w", err)
+	}
+	return nil
+}
+
+func installIngressForwardingRule(ctx context.Context, dstStr string, tsIPs []netip.Prefix) error {
 	dst, err := netip.ParseAddr(dstStr)
 	if err != nil {
 		return err
@@ -669,7 +739,14 @@ type settings struct {
 	AuthKey  string
 	Hostname string
 	Routes   string
+	// ProxyTo is the destination IP to which all incoming
+	// Tailscale traffic should be proxied. If empty, no proxying
+	// is done. This is typically a locally reachable IP.
 	ProxyTo string
+	// TailnetTargetIP is the destination IP to which all incoming
+	// non-Tailscale traffic should be proxied. If empty, no
+	// proxying is done. This is typically a Tailscale IP.
+	TailnetTargetIP    string
 	ServeConfigPath    string
 	DaemonExtraArgs    string
 	ExtraArgs          string

cmd/k8s-operator/ingress.go

@@ -190,7 +190,7 @@ func (a *IngressReconciler) maybeProvision(ctx context.Context, logger *zap.Suga
 		ChildResourceLabels: crl,
 	}
 
-	if err := a.ssr.Provision(ctx, logger, sts); err != nil {
+	if _, err := a.ssr.Provision(ctx, logger, sts); err != nil {
 		return fmt.Errorf("failed to provision: %w", err)
 	}
 

cmd/k8s-operator/operator_test.go

@@ -7,6 +7,7 @@ package main
 
 import (
 	"context"
+	"fmt"
 	"strings"
 	"sync"
 	"testing"
@@ -153,6 +154,111 @@ func TestLoadBalancerClass(t *testing.T) {
 	}
 	expectEqual(t, fc, want)
 }
+func TestTailnetTargetIPAnnotation(t *testing.T) {
+	fc := fake.NewFakeClient()
+	ft := &fakeTSClient{}
+	zl, err := zap.NewDevelopment()
+	if err != nil {
+		t.Fatal(err)
+	}
+	tailnetTargetIP := "100.66.66.66"
+	sr := &ServiceReconciler{
+		Client: fc,
+		ssr: &tailscaleSTSReconciler{
+			Client:            fc,
+			tsClient:          ft,
+			defaultTags:       []string{"tag:k8s"},
+			operatorNamespace: "operator-ns",
+			proxyImage:        "tailscale/tailscale",
+		},
+		logger: zl.Sugar(),
+	}
+
+	// Create a service that we should manage, and check that the initial round
+	// of objects looks right.
+	mustCreate(t, fc, &corev1.Service{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:      "test",
+			Namespace: "default",
+			// The apiserver is supposed to set the UID, but the fake client
+			// doesn't. So, set it explicitly because other code later depends
+			// on it being set.
+			UID: types.UID("1234-UID"),
+			Annotations: map[string]string{
+				AnnotationTailnetTargetIP: tailnetTargetIP,
+			},
+		},
+		Spec: corev1.ServiceSpec{
+			Type: corev1.ServiceTypeClusterIP,
+			Selector: map[string]string{
+				"foo": "bar",
+			},
+		},
+	})
+
+	expectReconciled(t, sr, "default", "test")
+
+	fullName, shortName := findGenName(t, fc, "default", "test")
+
+	expectEqual(t, fc, expectedSecret(fullName))
+	expectEqual(t, fc, expectedHeadlessService(shortName))
+	expectEqual(t, fc, expectedEgressSTS(shortName, fullName, tailnetTargetIP, "default-test", ""))
+	want := &corev1.Service{
+		TypeMeta: metav1.TypeMeta{
+			Kind:       "Service",
+			APIVersion: "v1",
+		},
+		ObjectMeta: metav1.ObjectMeta{
+			Name:       "test",
+			Namespace:  "default",
+			Finalizers: []string{"tailscale.com/finalizer"},
+			UID:        types.UID("1234-UID"),
+			Annotations: map[string]string{
+				AnnotationTailnetTargetIP: tailnetTargetIP,
+			},
+		},
+		Spec: corev1.ServiceSpec{
+			ExternalName: fmt.Sprintf("%s.operator-ns.svc", shortName),
+			Type:         corev1.ServiceTypeExternalName,
+			Selector:     nil,
+		},
+	}
+	expectEqual(t, fc, want)
+	expectEqual(t, fc, expectedSecret(fullName))
+	expectEqual(t, fc, expectedHeadlessService(shortName))
+	expectEqual(t, fc, expectedEgressSTS(shortName, fullName, tailnetTargetIP, "default-test", ""))
+
+	// Change the tailscale-target-ip annotation which should update the
+	// StatefulSet
+	tailnetTargetIP = "100.77.77.77"
+	mustUpdate(t, fc, "default", "test", func(s *corev1.Service) {
+		s.ObjectMeta.Annotations = map[string]string{
+			AnnotationTailnetTargetIP: tailnetTargetIP,
+		}
+	})
+
+	// Remove the tailscale-target-ip annotation which should make the
+	// operator clean up
+	mustUpdate(t, fc, "default", "test", func(s *corev1.Service) {
+		s.ObjectMeta.Annotations = map[string]string{}
+	})
+	expectReconciled(t, sr, "default", "test")
+
+	// // synchronous StatefulSet deletion triggers a requeue. But, the StatefulSet
+	// // didn't create any child resources since this is all faked, so the
+	// // deletion goes through immediately.
+	expectReconciled(t, sr, "default", "test")
+	expectMissing[appsv1.StatefulSet](t, fc, "operator-ns", shortName)
+	// // The deletion triggers another reconcile, to finish the cleanup.
+	expectReconciled(t, sr, "default", "test")
+	expectMissing[appsv1.StatefulSet](t, fc, "operator-ns", shortName)
+	expectMissing[corev1.Service](t, fc, "operator-ns", shortName)
+	expectMissing[corev1.Secret](t, fc, "operator-ns", fullName)
+
+	// At the moment we don't revert changes to the user created Service -
+	// we don't have a reliable way how to tell what it was before and also
+	// we don't really expect it to be re-used
+}
 
 func TestAnnotations(t *testing.T) {
 	fc := fake.NewFakeClient()
@@ -782,7 +888,7 @@ func expectedSTS(stsName, secretName, hostname, priorityClassName string) *appsv
 				ObjectMeta: metav1.ObjectMeta{
 					Annotations: map[string]string{
 						"tailscale.com/operator-last-set-hostname":   hostname,
-						"tailscale.com/operator-last-set-ip":       "10.20.30.40",
+						"tailscale.com/operator-last-set-cluster-ip": "10.20.30.40",
 					},
 					DeletionGracePeriodSeconds: ptr.To[int64](10),
 					Labels:                     map[string]string{"app": "1234-UID"},
@@ -825,6 +931,75 @@ func expectedSTS(stsName, secretName, hostname, priorityClassName string) *appsv
 		},
 	}
 }
+func expectedEgressSTS(stsName, secretName, tailnetTargetIP, hostname, priorityClassName string) *appsv1.StatefulSet {
+	return &appsv1.StatefulSet{
+		TypeMeta: metav1.TypeMeta{
+			Kind:       "StatefulSet",
+			APIVersion: "apps/v1",
+		},
+		ObjectMeta: metav1.ObjectMeta{
+			Name:      stsName,
+			Namespace: "operator-ns",
+			Labels: map[string]string{
+				"tailscale.com/managed":              "true",
+				"tailscale.com/parent-resource":      "test",
+				"tailscale.com/parent-resource-ns":   "default",
+				"tailscale.com/parent-resource-type": "svc",
+			},
+		},
+		Spec: appsv1.StatefulSetSpec{
+			Replicas: ptr.To[int32](1),
+			Selector: &metav1.LabelSelector{
+				MatchLabels: map[string]string{"app": "1234-UID"},
+			},
+			ServiceName: stsName,
+			Template: corev1.PodTemplateSpec{
+				ObjectMeta: metav1.ObjectMeta{
+					Annotations: map[string]string{
+						"tailscale.com/operator-last-set-hostname":             hostname,
+						"tailscale.com/operator-last-set-ts-tailnet-target-ip": tailnetTargetIP,
+					},
+					DeletionGracePeriodSeconds: ptr.To[int64](10),
+					Labels:                     map[string]string{"app": "1234-UID"},
+				},
+				Spec: corev1.PodSpec{
+					ServiceAccountName: "proxies",
+					PriorityClassName:  priorityClassName,
+					InitContainers: []corev1.Container{
+						{
+							Name:    "sysctler",
+							Image:   "busybox",
+							Command: []string{"/bin/sh"},
+							Args:    []string{"-c", "sysctl -w net.ipv4.ip_forward=1 net.ipv6.conf.all.forwarding=1"},
+							SecurityContext: &corev1.SecurityContext{
+								Privileged: ptr.To(true),
+							},
+						},
+					},
+					Containers: []corev1.Container{
+						{
+							Name:  "tailscale",
+							Image: "tailscale/tailscale",
+							Env: []corev1.EnvVar{
+								{Name: "TS_USERSPACE", Value: "false"},
+								{Name: "TS_AUTH_ONCE", Value: "true"},
+								{Name: "TS_KUBE_SECRET", Value: secretName},
+								{Name: "TS_HOSTNAME", Value: hostname},
+								{Name: "TS_TAILNET_TARGET_IP", Value: tailnetTargetIP},
+							},
+							SecurityContext: &corev1.SecurityContext{
+								Capabilities: &corev1.Capabilities{
+									Add: []corev1.Capability{"NET_ADMIN"},
+								},
+							},
+							ImagePullPolicy: "Always",
+						},
+					},
+				},
+			},
+		},
+	}
+}
 
 func findGenName(t *testing.T, client client.Client, ns, name string) (full, noSuffix string) {
 	t.Helper()

cmd/k8s-operator/sts.go

@@ -41,14 +41,16 @@ const (
 	AnnotationExpose          = "tailscale.com/expose"
 	AnnotationTags            = "tailscale.com/tags"
 	AnnotationHostname        = "tailscale.com/hostname"
+	AnnotationTailnetTargetIP = "tailscale.com/ts-tailnet-target-ip"
 
 	// Annotations settable by users on ingresses.
 	AnnotationFunnel = "tailscale.com/funnel"
 
 	// Annotations set by the operator on pods to trigger restarts when the
 	// hostname or IP changes.
-	podAnnotationLastSetIP       = "tailscale.com/operator-last-set-ip"
+	podAnnotationLastSetClusterIP       = "tailscale.com/operator-last-set-cluster-ip"
 	podAnnotationLastSetHostname        = "tailscale.com/operator-last-set-hostname"
+	podAnnotationLastSetTailnetTargetIP = "tailscale.com/operator-last-set-ts-tailnet-target-ip"
 )
 
 type tailscaleSTSConfig struct {
@@ -57,7 +59,11 @@ type tailscaleSTSConfig struct {
 	ChildResourceLabels map[string]string
 
 	ServeConfig *ipn.ServeConfig
-	TargetIP    string
+	// Tailscale target in cluster we are setting up ingress for
+	ClusterTargetIP string
+
+	// Tailscale IP of a Tailscale service we are setting up egress for
+	TailnetTargetIP string
 
 	Hostname string
 	Tags     []string // if empty, use defaultTags
@@ -74,23 +80,23 @@ type tailscaleSTSReconciler struct {
 
 // Provision ensures that the StatefulSet for the given service is running and
 // up to date.
-func (a *tailscaleSTSReconciler) Provision(ctx context.Context, logger *zap.SugaredLogger, sts *tailscaleSTSConfig) error {
+func (a *tailscaleSTSReconciler) Provision(ctx context.Context, logger *zap.SugaredLogger, sts *tailscaleSTSConfig) (*corev1.Service, error) {
 	// Do full reconcile.
 	hsvc, err := a.reconcileHeadlessService(ctx, logger, sts)
 	if err != nil {
-		return fmt.Errorf("failed to reconcile headless service: %w", err)
+		return nil, fmt.Errorf("failed to reconcile headless service: %w", err)
 	}
 
 	secretName, err := a.createOrGetSecret(ctx, logger, sts, hsvc)
 	if err != nil {
-		return fmt.Errorf("failed to create or get API key secret: %w", err)
+		return nil, fmt.Errorf("failed to create or get API key secret: %w", err)
 	}
 	_, err = a.reconcileSTS(ctx, logger, sts, hsvc, secretName)
 	if err != nil {
-		return fmt.Errorf("failed to reconcile statefulset: %w", err)
+		return nil, fmt.Errorf("failed to reconcile statefulset: %w", err)
 	}
 
-	return nil
+	return hsvc, nil
 }
 
 // Cleanup removes all resources associated that were created by Provision with
@@ -305,11 +311,17 @@ func (a *tailscaleSTSReconciler) reconcileSTS(ctx context.Context, logger *zap.S
 			Name:  "TS_HOSTNAME",
 			Value: sts.Hostname,
 		})
-	if sts.TargetIP != "" {
+	if sts.ClusterTargetIP != "" {
 		container.Env = append(container.Env, corev1.EnvVar{
 			Name:  "TS_DEST_IP",
-			Value: sts.TargetIP,
+			Value: sts.ClusterTargetIP,
+		})
+	} else if sts.TailnetTargetIP != "" {
+		container.Env = append(container.Env, corev1.EnvVar{
+			Name:  "TS_TAILNET_TARGET_IP",
+			Value: sts.TailnetTargetIP,
 		})
+
 	} else if sts.ServeConfig != nil {
 		container.Env = append(container.Env, corev1.EnvVar{
 			Name:  "TS_SERVE_CONFIG",
@@ -350,10 +362,13 @@ func (a *tailscaleSTSReconciler) reconcileSTS(ctx context.Context, logger *zap.S
 	// container when the value changes. We do this by adding an annotation to
 	// the pod template that contains the last value we set.
 	ss.Spec.Template.Annotations = map[string]string{
-		"tailscale.com/operator-last-set-hostname": sts.Hostname,
+		podAnnotationLastSetHostname: sts.Hostname,
+	}
+	if sts.ClusterTargetIP != "" {
+		ss.Spec.Template.Annotations[podAnnotationLastSetClusterIP] = sts.ClusterTargetIP
 	}
-	if sts.TargetIP != "" {
+	if sts.TailnetTargetIP != "" {
-		ss.Spec.Template.Annotations["tailscale.com/operator-last-set-ip"] = sts.TargetIP
+		ss.Spec.Template.Annotations[podAnnotationLastSetTailnetTargetIP] = sts.TailnetTargetIP
 	}
 	ss.Spec.Template.Labels = map[string]string{
 		"app": sts.ParentResourceUID,

cmd/k8s-operator/svc.go

@@ -55,8 +55,8 @@ func (a *ServiceReconciler) Reconcile(ctx context.Context, req reconcile.Request
 	} else if err != nil {
 		return reconcile.Result{}, fmt.Errorf("failed to get svc: %w", err)
 	}
-	if !svc.DeletionTimestamp.IsZero() || !a.shouldExpose(svc) {
+	if !svc.DeletionTimestamp.IsZero() || !a.shouldExpose(svc) && !a.hasTailnetTargetAnnotation(svc) {
-		logger.Debugf("service is being deleted or should not be exposed, cleaning up")
+		logger.Debugf("service is being deleted or is (no longer) referring to Tailscale ingress/egress, ensuring any created resources are cleaned up")
 		return reconcile.Result{}, a.maybeCleanup(ctx, logger, svc)
 	}
 
@@ -122,24 +122,34 @@ func (a *ServiceReconciler) maybeProvision(ctx context.Context, logger *zap.Suga
 		tags = strings.Split(tstr, ",")
 	}
 
-	clusterIPAddr, err := netip.ParseAddr(svc.Spec.ClusterIP)
-	if err != nil {
-		return fmt.Errorf("failed to parse cluster IP: %w", err)
-	}
-
 	sts := &tailscaleSTSConfig{
 		ParentResourceName:  svc.Name,
 		ParentResourceUID:   string(svc.UID),
-		TargetIP:            svc.Spec.ClusterIP,
+		ClusterTargetIP:     svc.Spec.ClusterIP,
 		Hostname:            hostname,
 		Tags:                tags,
 		ChildResourceLabels: crl,
+		TailnetTargetIP:     svc.Annotations[AnnotationTailnetTargetIP],
 	}
 
-	if err := a.ssr.Provision(ctx, logger, sts); err != nil {
+	var hsvc *corev1.Service
+	if hsvc, err = a.ssr.Provision(ctx, logger, sts); err != nil {
 		return fmt.Errorf("failed to provision: %w", err)
 	}
 
+	if a.hasTailnetTargetAnnotation(svc) {
+		headlessSvcName := hsvc.Name + "." + hsvc.Namespace + ".svc"
+		if svc.Spec.ExternalName != headlessSvcName || svc.Spec.Type != corev1.ServiceTypeExternalName {
+			svc.Spec.ExternalName = headlessSvcName
+			svc.Spec.Selector = nil
+			svc.Spec.Type = corev1.ServiceTypeExternalName
+			if err := a.Update(ctx, svc); err != nil {
+				return fmt.Errorf("failed to update service: %w", err)
+			}
+		}
+		return nil
+	}
+
 	if !a.hasLoadBalancerClass(svc) {
 		logger.Debugf("service is not a LoadBalancer, so not updating ingress")
 		return nil
@@ -163,6 +173,10 @@ func (a *ServiceReconciler) maybeProvision(ctx context.Context, logger *zap.Suga
 	ingress := []corev1.LoadBalancerIngress{
 		{Hostname: tsHost},
 	}
+	clusterIPAddr, err := netip.ParseAddr(svc.Spec.ClusterIP)
+	if err != nil {
+		return fmt.Errorf("failed to parse cluster IP: %w", err)
+	}
 	for _, ip := range tsIPs {
 		addr, err := netip.ParseAddr(ip)
 		if err != nil {
@@ -186,7 +200,7 @@ func (a *ServiceReconciler) shouldExpose(svc *corev1.Service) bool {
 		return false
 	}
 
-	return a.hasLoadBalancerClass(svc) || a.hasAnnotation(svc)
+	return a.hasLoadBalancerClass(svc) || a.hasExposeAnnotation(svc)
 }
 
 func (a *ServiceReconciler) hasLoadBalancerClass(svc *corev1.Service) bool {
@@ -196,7 +210,14 @@ func (a *ServiceReconciler) hasLoadBalancerClass(svc *corev1.Service) bool {
 			svc.Spec.LoadBalancerClass == nil && a.isDefaultLoadBalancer)
 }
 
-func (a *ServiceReconciler) hasAnnotation(svc *corev1.Service) bool {
+// hasExposeAnnotation reports whether Service has the tailscale.com/expose
-	return svc != nil &&
+// annotation set
-		svc.Annotations[AnnotationExpose] == "true"
+func (a *ServiceReconciler) hasExposeAnnotation(svc *corev1.Service) bool {
+	return svc != nil && svc.Annotations[AnnotationExpose] == "true"
+}
+
+// hasTailnetTargetAnnotation reports whether Service has a
+// tailscale.com/ts-tailnet-target-ip annotation set
+func (a *ServiceReconciler) hasTailnetTargetAnnotation(svc *corev1.Service) bool {
+	return svc != nil && svc.Annotations[AnnotationTailnetTargetIP] != ""
 }