cmd/tailscale/cli: make configure kubeconfig accept Tailscale Services (#16601)

The Kubernetes API server proxy is getting the ability to serve on a
Tailscale Service instead of individual node names. Update the configure
kubeconfig sub-command to accept arguments that look like a Tailscale
Service. Note, we can't know for sure whether a peer is advertising a
Tailscale Service, we can only guess based on the ExtraRecords in the
netmap and that IP showing up in a peer's AllowedIPs.

Also adds an --http flag to allow targeting individual proxies that can
be adverting on http for their node name, and makes the command a bit
more forgiving on the range of inputs it accepts and how eager it is to
print the help text when the input is obviously wrong.

Updates #13358

Change-Id: Ica0509c6b2c707252a43d7c18b530ec1acf7508f

Signed-off-by: Tom Proctor <tomhjp@users.noreply.github.com>

cmd/tailscale/cli/configure-kube.go

@@ -9,17 +9,29 @@ import (
 	"errors"
 	"flag"
 	"fmt"
+	"net/netip"
+	"net/url"
 	"os"
 	"path/filepath"
 	"slices"
 	"strings"
+	"time"
 
 	"github.com/peterbourgon/ff/v3/ffcli"
 	"k8s.io/client-go/util/homedir"
 	"sigs.k8s.io/yaml"
+	"tailscale.com/ipn"
+	"tailscale.com/ipn/ipnstate"
+	"tailscale.com/tailcfg"
+	"tailscale.com/types/netmap"
+	"tailscale.com/util/dnsname"
 	"tailscale.com/version"
 )
 
+var configureKubeconfigArgs struct {
+	http bool // Use HTTP instead of HTTPS (default) for the auth proxy.
+}
+
 func configureKubeconfigCmd() *ffcli.Command {
 	return &ffcli.Command{
 		Name:       "kubeconfig",
@@ -34,6 +46,7 @@ See: https://tailscale.com/s/k8s-auth-proxy
 `),
 		FlagSet: (func() *flag.FlagSet {
 			fs := newFlagSet("kubeconfig")
+			fs.BoolVar(&configureKubeconfigArgs.http, "http", false, "Use HTTP instead of HTTPS to connect to the auth proxy. Ignored if you include a scheme in the hostname argument.")
 			return fs
 		})(),
 		Exec: runConfigureKubeconfig,
@@ -70,10 +83,13 @@ func kubeconfigPath() (string, error) {
 }
 
 func runConfigureKubeconfig(ctx context.Context, args []string) error {
-	if len(args) != 1 {
-		return errors.New("unknown arguments")
+	if len(args) != 1 || args[0] == "" {
+		return flag.ErrHelp
+	}
+	hostOrFQDNOrIP, http, err := getInputs(args[0], configureKubeconfigArgs.http)
+	if err != nil {
+		return fmt.Errorf("error parsing inputs: %w", err)
 	}
-	hostOrFQDN := args[0]
 
 	st, err := localClient.Status(ctx)
 	if err != nil {
@@ -82,22 +98,45 @@ func runConfigureKubeconfig(ctx context.Context, args []string) error {
 	if st.BackendState != "Running" {
 		return errors.New("Tailscale is not running")
 	}
-	targetFQDN, ok := nodeDNSNameFromArg(st, hostOrFQDN)
-	if !ok {
-		return fmt.Errorf("no peer found with hostname %q", hostOrFQDN)
+	nm, err := getNetMap(ctx)
+	if err != nil {
+		return err
+	}
+
+	targetFQDN, err := nodeOrServiceDNSNameFromArg(st, nm, hostOrFQDNOrIP)
+	if err != nil {
+		return err
 	}
 	targetFQDN = strings.TrimSuffix(targetFQDN, ".")
 	var kubeconfig string
 	if kubeconfig, err = kubeconfigPath(); err != nil {
 		return err
 	}
-	if err = setKubeconfigForPeer(targetFQDN, kubeconfig); err != nil {
+	scheme := "https://"
+	if http {
+		scheme = "http://"
+	}
+	if err = setKubeconfigForPeer(scheme, targetFQDN, kubeconfig); err != nil {
 		return err
 	}
-	printf("kubeconfig configured for %q\n", hostOrFQDN)
+	printf("kubeconfig configured for %q at URL %q\n", targetFQDN, scheme+targetFQDN)
 	return nil
 }
 
+func getInputs(arg string, httpArg bool) (string, bool, error) {
+	u, err := url.Parse(arg)
+	if err != nil {
+		return "", false, err
+	}
+
+	switch u.Scheme {
+	case "http", "https":
+		return u.Host, u.Scheme == "http", nil
+	default:
+		return arg, httpArg, nil
+	}
+}
+
 // appendOrSetNamed finds a map with a "name" key matching name in dst, and
 // replaces it with val. If no such map is found, val is appended to dst.
 func appendOrSetNamed(dst []any, name string, val map[string]any) []any {
@@ -116,7 +155,7 @@ func appendOrSetNamed(dst []any, name string, val map[string]any) []any {
 
 var errInvalidKubeconfig = errors.New("invalid kubeconfig")
 
-func updateKubeconfig(cfgYaml []byte, fqdn string) ([]byte, error) {
+func updateKubeconfig(cfgYaml []byte, scheme, fqdn string) ([]byte, error) {
 	var cfg map[string]any
 	if len(cfgYaml) > 0 {
 		if err := yaml.Unmarshal(cfgYaml, &cfg); err != nil {
@@ -139,7 +178,7 @@ func updateKubeconfig(cfgYaml []byte, fqdn string) ([]byte, error) {
 	cfg["clusters"] = appendOrSetNamed(clusters, fqdn, map[string]any{
 		"name": fqdn,
 		"cluster": map[string]string{
-			"server": "https://" + fqdn,
+			"server": scheme + fqdn,
 		},
 	})
 
@@ -172,7 +211,7 @@ func updateKubeconfig(cfgYaml []byte, fqdn string) ([]byte, error) {
 	return yaml.Marshal(cfg)
 }
 
-func setKubeconfigForPeer(fqdn, filePath string) error {
+func setKubeconfigForPeer(scheme, fqdn, filePath string) error {
 	dir := filepath.Dir(filePath)
 	if _, err := os.Stat(dir); err != nil {
 		if !os.IsNotExist(err) {
@@ -191,9 +230,97 @@ func setKubeconfigForPeer(fqdn, filePath string) error {
 	if err != nil && !os.IsNotExist(err) {
 		return fmt.Errorf("reading kubeconfig: %w", err)
 	}
-	b, err = updateKubeconfig(b, fqdn)
+	b, err = updateKubeconfig(b, scheme, fqdn)
 	if err != nil {
 		return err
 	}
 	return os.WriteFile(filePath, b, 0600)
 }
+
+// nodeOrServiceDNSNameFromArg returns the PeerStatus.DNSName value from a peer
+// in st that matches the input arg which can be a base name, full DNS name, or
+// an IP. If none is found, it looks for a Tailscale Service
+func nodeOrServiceDNSNameFromArg(st *ipnstate.Status, nm *netmap.NetworkMap, arg string) (string, error) {
+	// First check for a node DNS name.
+	if dnsName, ok := nodeDNSNameFromArg(st, arg); ok {
+		return dnsName, nil
+	}
+
+	// If not found, check for a Tailscale Service DNS name.
+	rec, ok := serviceDNSRecordFromNetMap(nm, st.CurrentTailnet.MagicDNSSuffix, arg)
+	if !ok {
+		return "", fmt.Errorf("no peer found for %q", arg)
+	}
+
+	// Validate we can see a peer advertising the Tailscale Service.
+	ip, err := netip.ParseAddr(rec.Value)
+	if err != nil {
+		return "", fmt.Errorf("error parsing ExtraRecord IP address %q: %w", rec.Value, err)
+	}
+	ipPrefix := netip.PrefixFrom(ip, ip.BitLen())
+	for _, ps := range st.Peer {
+		for _, allowedIP := range ps.AllowedIPs.All() {
+			if allowedIP == ipPrefix {
+				return rec.Name, nil
+			}
+		}
+	}
+
+	return "", fmt.Errorf("%q is in MagicDNS, but is not currently reachable on any known peer", arg)
+}
+
+func getNetMap(ctx context.Context) (*netmap.NetworkMap, error) {
+	ctx, cancel := context.WithTimeout(ctx, 5*time.Second)
+	defer cancel()
+
+	watcher, err := localClient.WatchIPNBus(ctx, ipn.NotifyInitialNetMap)
+	if err != nil {
+		return nil, err
+	}
+	defer watcher.Close()
+
+	n, err := watcher.Next()
+	if err != nil {
+		return nil, err
+	}
+
+	return n.NetMap, nil
+}
+
+func serviceDNSRecordFromNetMap(nm *netmap.NetworkMap, tcd, arg string) (rec tailcfg.DNSRecord, ok bool) {
+	argIP, _ := netip.ParseAddr(arg)
+	argFQDN, err := dnsname.ToFQDN(arg)
+	argFQDNValid := err == nil
+	if !argIP.IsValid() && !argFQDNValid {
+		return rec, false
+	}
+
+	for _, rec := range nm.DNS.ExtraRecords {
+		if argIP.IsValid() {
+			recIP, _ := netip.ParseAddr(rec.Value)
+			if recIP == argIP {
+				return rec, true
+			}
+			continue
+		}
+
+		if !argFQDNValid {
+			continue
+		}
+
+		recFirstLabel := dnsname.FirstLabel(rec.Name)
+		if strings.EqualFold(arg, recFirstLabel) {
+			return rec, true
+		}
+
+		recFQDN, err := dnsname.ToFQDN(rec.Name)
+		if err != nil {
+			continue
+		}
+		if strings.EqualFold(argFQDN.WithTrailingDot(), recFQDN.WithTrailingDot()) {
+			return rec, true
+		}
+	}
+
+	return tailcfg.DNSRecord{}, false
+}

cmd/tailscale/cli/configure-kube_test.go

@@ -6,6 +6,7 @@ package cli
 
 import (
 	"bytes"
+	"fmt"
 	"strings"
 	"testing"
 
@@ -16,6 +17,7 @@ func TestKubeconfig(t *testing.T) {
 	const fqdn = "foo.tail-scale.ts.net"
 	tests := []struct {
 		name    string
+		http    bool
 		in      string
 		want    string
 		wantErr error
@@ -48,6 +50,27 @@ contexts:
 current-context: foo.tail-scale.ts.net
 kind: Config
 users:
+- name: tailscale-auth
+  user:
+    token: unused`,
+		},
+		{
+			name: "empty_http",
+			http: true,
+			in:   "",
+			want: `apiVersion: v1
+clusters:
+- cluster:
+    server: http://foo.tail-scale.ts.net
+  name: foo.tail-scale.ts.net
+contexts:
+- context:
+    cluster: foo.tail-scale.ts.net
+    user: tailscale-auth
+  name: foo.tail-scale.ts.net
+current-context: foo.tail-scale.ts.net
+kind: Config
+users:
 - name: tailscale-auth
   user:
     token: unused`,
@@ -202,7 +225,11 @@ users:
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			got, err := updateKubeconfig([]byte(tt.in), fqdn)
+			scheme := "https://"
+			if tt.http {
+				scheme = "http://"
+			}
+			got, err := updateKubeconfig([]byte(tt.in), scheme, fqdn)
 			if err != nil {
 				if err != tt.wantErr {
 					t.Fatalf("updateKubeconfig() error = %v, wantErr %v", err, tt.wantErr)
@@ -219,3 +246,30 @@ users:
 		})
 	}
 }
+
+func TestGetInputs(t *testing.T) {
+	for _, arg := range []string{
+		"foo.tail-scale.ts.net",
+		"foo",
+		"127.0.0.1",
+	} {
+		for _, prefix := range []string{"", "https://", "http://"} {
+			for _, httpFlag := range []bool{false, true} {
+				expectedHost := arg
+				expectedHTTP := (httpFlag && !strings.HasPrefix(prefix, "https://")) || strings.HasPrefix(prefix, "http://")
+				t.Run(fmt.Sprintf("%s%s_http=%v", prefix, arg, httpFlag), func(t *testing.T) {
+					host, http, err := getInputs(prefix+arg, httpFlag)
+					if err != nil {
+						t.Fatal(err)
+					}
+					if host != expectedHost {
+						t.Errorf("host = %v, want %v", host, expectedHost)
+					}
+					if http != expectedHTTP {
+						t.Errorf("http = %v, want %v", http, expectedHTTP)
+					}
+				})
+			}
+		}
+	}
+}