cmd/tailscale/cli: add advertise command to advertise a node as service proxy to tailnet (#16620)

This commit adds a advertise subcommand for tailscale serve, that would declare the node
as a service proxy for a service. This command only adds the service to node's list of
advertised service, but doesn't modify the list of services currently advertised.

Fixes tailscale/corp#28016

Signed-off-by: KevinLiang10 <37811973+KevinLiang10@users.noreply.github.com>

cmd/tailscale/cli/serve_v2.go

@@ -220,6 +220,16 @@ func newServeV2Command(e *serveEnv, subcmd serveMode) *ffcli.Command {
 				LongHelp:   "Remove all handlers configured for the specified service.",
 				Exec:       e.runServeClear,
 			},
+			{
+				Name:       "advertise",
+				ShortUsage: fmt.Sprintf("tailscale %s advertise <service>", info.Name),
+				ShortHelp:  "Advertise this node as a service proxy to the tailnet",
+				LongHelp: "Advertise this node as a service proxy to the tailnet. This command is used\n" +
+					"to make the current node be considered as a service host for a service. This is\n" +
+					"useful to bring a service back after it has been drained. (i.e. after running \n" +
+					"`tailscale serve drain <service>`). This is not needed if you are using `tailscale serve` to initialize a service.",
+				Exec: e.runServeAdvertise,
+			},
 		},
 	}
 }
@@ -401,7 +411,7 @@ func (e *serveEnv) runServeCombined(subcmd serveMode) execFunc {
 				return err
 			}
 			if forService {
-				e.addServiceToPrefs(ctx, svcName.String())
+				e.addServiceToPrefs(ctx, svcName)
 			}
 			target := ""
 			if len(args) > 0 {
@@ -442,16 +452,16 @@ func (e *serveEnv) runServeCombined(subcmd serveMode) execFunc {
 	}
 }
 
-func (e *serveEnv) addServiceToPrefs(ctx context.Context, serviceName string) error {
+func (e *serveEnv) addServiceToPrefs(ctx context.Context, serviceName tailcfg.ServiceName) error {
 	prefs, err := e.lc.GetPrefs(ctx)
 	if err != nil {
 		return fmt.Errorf("error getting prefs: %w", err)
 	}
 	advertisedServices := prefs.AdvertiseServices
-	if slices.Contains(advertisedServices, serviceName) {
+	if slices.Contains(advertisedServices, serviceName.String()) {
 		return nil // already advertised
 	}
-	advertisedServices = append(advertisedServices, serviceName)
+	advertisedServices = append(advertisedServices, serviceName.String())
 	_, err = e.lc.EditPrefs(ctx, &ipn.MaskedPrefs{
 		AdvertiseServicesSet: true,
 		Prefs: ipn.Prefs{
@@ -526,6 +536,21 @@ func (e *serveEnv) runServeClear(ctx context.Context, args []string) error {
 	return e.lc.SetServeConfig(ctx, sc)
 }
 
+func (e *serveEnv) runServeAdvertise(ctx context.Context, args []string) error {
+	if len(args) == 0 {
+		return fmt.Errorf("error: missing service name argument")
+	}
+	if len(args) != 1 {
+		fmt.Fprintf(Stderr, "error: invalid number of arguments\n\n")
+		return errHelp
+	}
+	svc := tailcfg.ServiceName(args[0])
+	if err := svc.Validate(); err != nil {
+		return fmt.Errorf("invalid service name: %w", err)
+	}
+	return e.addServiceToPrefs(ctx, svc)
+}
+
 const backgroundExistsMsg = "background configuration already exists, use `tailscale %s --%s=%d off` to remove the existing configuration"
 
 // validateConfig checks if the serve config is valid to serve the type wanted on the port.

cmd/tailscale/cli/serve_v2_test.go

@@ -1167,24 +1167,24 @@ func TestCleanURLPath(t *testing.T) {
 func TestAddServiceToPrefs(t *testing.T) {
 	tests := []struct {
 		name          string
-		dnsName       string
+		svcName       tailcfg.ServiceName
 		startServices []string
 		expected      []string
 	}{
 		{
 			name:     "add service to empty prefs",
-			dnsName:  "svc:foo",
+			svcName:  "svc:foo",
 			expected: []string{"svc:foo"},
 		},
 		{
 			name:          "add service to existing prefs",
-			dnsName:       "svc:bar",
+			svcName:       "svc:bar",
 			startServices: []string{"svc:foo"},
 			expected:      []string{"svc:foo", "svc:bar"},
 		},
 		{
 			name:          "add existing service to prefs",
-			dnsName:       "svc:foo",
+			svcName:       "svc:foo",
 			startServices: []string{"svc:foo"},
 			expected:      []string{"svc:foo"},
 		},
@@ -1200,12 +1200,12 @@ func TestAddServiceToPrefs(t *testing.T) {
 				},
 			})
 			e := &serveEnv{lc: lc, bg: bgBoolFlag{true, false}}
-			err := e.addServiceToPrefs(ctx, tt.dnsName)
+			err := e.addServiceToPrefs(ctx, tt.svcName)
 			if err != nil {
-				t.Fatalf("addServiceToPrefs(%q) returned unexpected error: %v", tt.dnsName, err)
+				t.Fatalf("addServiceToPrefs(%q) returned unexpected error: %v", tt.svcName, err)
 			}
 			if !slices.Equal(lc.prefs.AdvertiseServices, tt.expected) {
-				t.Errorf("addServiceToPrefs(%q) = %v, want %v", tt.dnsName, lc.prefs.AdvertiseServices, tt.expected)
+				t.Errorf("addServiceToPrefs(%q) = %v, want %v", tt.svcName, lc.prefs.AdvertiseServices, tt.expected)
 			}
 		})
 	}