cmd/tailscale/cli/cli_test.go

@@ -30,6 +30,7 @@ import (
 	"tailscale.com/tka"
 	"tailscale.com/tstest"
 	"tailscale.com/tstest/deptest"
+	"tailscale.com/types/key"
 	"tailscale.com/types/logger"
 	"tailscale.com/types/opt"
 	"tailscale.com/types/persist"
@@ -769,7 +770,22 @@ func TestPrefsFromUpArgs(t *testing.T) {
 			args: upArgsT{
 				exitNodeIP: "foo",
 			},
-			wantErr: `invalid value "foo" for --exit-node; must be IP or hostname`,
+			st: &ipnstate.Status{
+				Peer: map[key.NodePublic]*ipnstate.PeerStatus{
+					key.NewNode().Public(): {
+						DNSName:      "example.com.",
+						TailscaleIPs: []netip.Addr{netip.MustParseAddr("1.0.0.2")},
+					},
+				},
+			},
+			wantErr: `invalid value "foo" for --exit-node; must be IP or peer hostname`,
+		},
+		{
+			name: "error_exit_node_not_started",
+			args: upArgsT{
+				exitNodeIP: "foo",
+			},
+			wantErr: `cannot resolve exit node by hostname while Tailscale is starting up; please use its Tailscale IP address instead`,
 		},
 		{
 			name: "error_exit_node_allow_lan_without_exit_node",

ipn/prefs.go

@@ -872,10 +872,14 @@ func (e ExitNodeLocalIPError) Error() string {
 	return fmt.Sprintf("cannot use %s as an exit node as it is a local IP address to this machine", e.hostOrIP)
 }
 
+// exitNodeIPOfArg returns the IP address of the exit node based on the
+// user-provided string.
 func exitNodeIPOfArg(s string, st *ipnstate.Status) (ip netip.Addr, err error) {
 	if s == "" {
 		return ip, os.ErrInvalid
 	}
+
+	// If the string is a valid IP address, that's the exit node.
 	ip, err = netip.ParseAddr(s)
 	if err == nil {
 		if !isRemoteIP(st, ip) {
@@ -894,6 +898,13 @@ func exitNodeIPOfArg(s string, st *ipnstate.Status) (ip netip.Addr, err error) {
 		}
 		return ip, nil
 	}
+
+	// If the string is not a valid IP address, assume it's a hostname.
+	// Search the list of peers for a matching hostname.
+	if len(st.Peer) == 0 {
+		return ip, errors.New("cannot resolve exit node by hostname while Tailscale is starting up; " +
+			"please use its Tailscale IP address instead")
+	}
 	match := 0
 	for _, ps := range st.Peer {
 		// Compare to the peer name in three forms:
@@ -920,7 +931,7 @@ func exitNodeIPOfArg(s string, st *ipnstate.Status) (ip netip.Addr, err error) {
 	}
 	switch match {
 	case 0:
-		return ip, fmt.Errorf("invalid value %q for --exit-node; must be IP or hostname", s)
+		return ip, fmt.Errorf("invalid value %q for --exit-node; must be IP or peer hostname", s)
 	case 1:
 		if !isRemoteIP(st, ip) {
 			return ip, ExitNodeLocalIPError{s}

ipn/prefs_test.go

@@ -1006,10 +1006,19 @@ func TestExitNodeIPOfArg(t *testing.T) {
 			want: mustIP("1.2.3.4"),
 		},
 		{
-			name:    "no_match",
-			arg:     "unknown",
-			st:      &ipnstate.Status{MagicDNSSuffix: ".foo"},
-			wantErr: `invalid value "unknown" for --exit-node; must be IP or hostname`,
+			name: "no_match",
+			arg:  "unknown",
+			st: &ipnstate.Status{
+				MagicDNSSuffix: ".foo",
+				Peer: map[key.NodePublic]*ipnstate.PeerStatus{
+					key.NewNode().Public(): {
+						DNSName:        "skippy.foo.",
+						TailscaleIPs:   []netip.Addr{mustIP("1.0.0.2")},
+						ExitNodeOption: true,
+					},
+				},
+			},
+			wantErr: `invalid value "unknown" for --exit-node; must be IP or peer hostname`,
 		},
 		{
 			name: "name",
@@ -1056,6 +1065,12 @@ func TestExitNodeIPOfArg(t *testing.T) {
 			},
 			want: mustIP("1.0.0.2"),
 		},
+		{
+			name:    "hostname_no_peer",
+			arg:     "skippy.foo",
+			st:      &ipnstate.Status{},
+			wantErr: `cannot resolve exit node by hostname while Tailscale is starting up; please use its Tailscale IP address instead`,
+		},
 		{
 			name: "name_not_exit",
 			arg:  "skippy",
@@ -1082,7 +1097,7 @@ func TestExitNodeIPOfArg(t *testing.T) {
 					},
 				},
 			},
-			wantErr: `invalid value "skippy.bar." for --exit-node; must be IP or hostname`,
+			wantErr: `invalid value "skippy.bar." for --exit-node; must be IP or peer hostname`,
 		},
 		{
 			name: "ambiguous",