add config option for node hostname

app.go

@@ -47,6 +47,9 @@ type Node struct {
 	// Ephemeral specifies whether the node should be registered as ephemeral.
 	Ephemeral bool `json:"ephemeral,omitempty" caddy:"namespace=tailscale.ephemeral"`
 
+	// Hostname is the hostname to use when registering the node.
+	Hostname string `json:"hostname,omitempty" caddy:"namespace=tailscale.hostname"`
+
 	name string
 }
 
@@ -137,6 +140,11 @@ func parseNodeConfig(d *caddyfile.Dispenser) (Node, error) {
 			node.ControlURL = segment.Val()
 		case "ephemeral":
 			node.Ephemeral = true
+		case "hostname":
+			if !segment.NextArg() {
+				return node, segment.ArgErr()
+			}
+			node.Hostname = segment.Val()
 		default:
 			return node, segment.Errf("unrecognized subdirective: %s", segment.Val())
 		}

module.go

@@ -103,7 +103,6 @@ func getNode(ctx caddy.Context, name string) (*tailscaleNode, error) {
 
 	s, _, err := nodes.LoadOrNew(name, func() (caddy.Destructor, error) {
 		s := &tsnet.Server{
-			Hostname: name,
 			Logf: func(format string, args ...any) {
 				app.logger.Sugar().Debugf(format, args...)
 			},
@@ -116,6 +115,9 @@ func getNode(ctx caddy.Context, name string) (*tailscaleNode, error) {
 		if s.ControlURL, err = getControlURL(name, app); err != nil {
 			return nil, err
 		}
+		if s.Hostname, err = getHostname(name, app); err != nil {
+			return nil, err
+		}
 
 		if name != "" {
 			// Set config directory for tsnet.  By default, tsnet will use the name of the
@@ -182,6 +184,19 @@ func getEphemeral(name string, app *App) bool {
 	return app.Ephemeral
 }
 
+func getHostname(name string, app *App) (string, error) {
+	if app == nil {
+		return name, nil
+	}
+	if node, ok := app.Nodes[name]; ok {
+		if node.Hostname != "" {
+			return repl.ReplaceOrErr(node.Hostname, true, true)
+		}
+	}
+
+	return name, nil
+}
+
 // tailscaleNode is a wrapper around a tsnet.Server that provides a fully self-contained Tailscale node.
 // This node can listen on the tailscale network interface, or be used to connect to other nodes in the tailnet.
 type tailscaleNode struct {

module_test.go

@@ -81,6 +81,99 @@ func Test_GetAuthKey(t *testing.T) {
 	}
 }
 
+func Test_GetControlURL(t *testing.T) {
+	const nodeName = "node"
+	tests := map[string]struct {
+		env        map[string]string // env vars to set
+		defaultURL string            // default control_url in caddy config
+		nodeURL    string            // node control_url in caddy config
+		want       string
+	}{
+		"default empty URL": {
+			want: "",
+		},
+		"custom URL from app config": {
+			defaultURL: "http://custom.example.com",
+			want:       "http://custom.example.com",
+		},
+		"custom URL from node config": {
+			defaultURL: "xxx",
+			nodeURL:    "http://custom.example.com",
+			want:       "http://custom.example.com",
+		},
+		"custom URL from env on app config": {
+			env:        map[string]string{"CONTROL_URL": "http://env.example.com"},
+			defaultURL: "{env.CONTROL_URL}",
+			want:       "http://env.example.com",
+		},
+		"custom URL from env on node config": {
+			env:        map[string]string{"CONTROL_URL": "http://env.example.com"},
+			defaultURL: "xxx",
+			nodeURL:    "{env.CONTROL_URL}",
+			want:       "http://env.example.com",
+		},
+	}
+	for tn, tt := range tests {
+		t.Run(tn, func(t *testing.T) {
+			app := &App{
+				ControlURL: tt.defaultURL,
+				Nodes:      make(map[string]Node),
+			}
+			if tt.nodeURL != "" {
+				app.Nodes[nodeName] = Node{
+					ControlURL: tt.nodeURL,
+				}
+			}
+			app.Provision(caddy.Context{})
+			for k, v := range tt.env {
+				t.Setenv(k, v)
+			}
+
+			got, _ := getControlURL(nodeName, app)
+			if got != tt.want {
+				t.Errorf("GetControlURL() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+func Test_GetHostname(t *testing.T) {
+	const nodeName = "node"
+	tests := map[string]struct {
+		env      map[string]string // env vars to set
+		hostname string            // hostname value in caddy config
+		want     string
+	}{
+		"default hostname from node name": {
+			want: nodeName,
+		},
+		"custom hostname from node config": {
+			hostname: "custom",
+			want:     "custom",
+		},
+		"custom hostname with env vars": {
+			env:      map[string]string{"REGION": "eu", "ENV": "prod"},
+			hostname: "custom-{env.REGION}-{env.ENV}",
+			want:     "custom-eu-prod",
+		},
+	}
+	for tn, tt := range tests {
+		t.Run(tn, func(t *testing.T) {
+			app := &App{Nodes: map[string]Node{
+				nodeName: {Hostname: tt.hostname},
+			}}
+			app.Provision(caddy.Context{})
+			for k, v := range tt.env {
+				t.Setenv(k, v)
+			}
+
+			got, _ := getHostname(nodeName, app)
+			if got != tt.want {
+				t.Errorf("GetHostname() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
 func Test_Listen(t *testing.T) {
 	must.Do(caddy.Run(new(caddy.Config)))
 	ctx := caddy.ActiveContext()