all: remove everything related to non-seamless key renewal

Seamless key renewal has been the default in all clients since 1.90.
We retained the ability to disable it from the control plane as a
precaution, but we haven't seen any issues that require us to disable it.

We're now removing all the code for non-seamless key renewal, because we
don't expect to turn it on again, and indeed it's been untested in the
field for three releases so might contain latent bugs!

Updates tailscale/corp#33042

Change-Id: I4b80bf07a3a50298d1c303743484169accc8844b
Signed-off-by: Alex Chan <alexc@tailscale.com>

control/controlknobs/controlknobs.go

@@ -62,12 +62,6 @@ type Knobs struct {
 	// netfiltering, unless overridden by the user.
 	LinuxForceNfTables atomic.Bool
 
-	// SeamlessKeyRenewal is whether to renew node keys without breaking connections.
-	// This is enabled by default in 1.90 and later, but we but we can remotely disable
-	// it from the control plane if there's a problem.
-	// http://go/seamless-key-renewal
-	SeamlessKeyRenewal atomic.Bool
-
 	// ProbeUDPLifetime is whether the node should probe UDP path lifetime on
 	// the tail end of an active direct connection in magicsock.
 	ProbeUDPLifetime atomic.Bool
@@ -142,8 +136,6 @@ func (k *Knobs) UpdateFromNodeAttributes(capMap tailcfg.NodeCapMap) {
 		silentDisco                          = has(tailcfg.NodeAttrSilentDisco)
 		forceIPTables                        = has(tailcfg.NodeAttrLinuxMustUseIPTables)
 		forceNfTables                        = has(tailcfg.NodeAttrLinuxMustUseNfTables)
-		seamlessKeyRenewal                   = has(tailcfg.NodeAttrSeamlessKeyRenewal)
-		disableSeamlessKeyRenewal            = has(tailcfg.NodeAttrDisableSeamlessKeyRenewal)
 		probeUDPLifetime                     = has(tailcfg.NodeAttrProbeUDPLifetime)
 		appCStoreRoutes                      = has(tailcfg.NodeAttrStoreAppCRoutes)
 		userDialUseRoutes                    = has(tailcfg.NodeAttrUserDialUseRoutes)
@@ -181,21 +173,6 @@ func (k *Knobs) UpdateFromNodeAttributes(capMap tailcfg.NodeCapMap) {
 	k.DisableSkipStatusQueue.Store(disableSkipStatusQueue)
 	k.DisableHostsFileUpdates.Store(disableHostsFileUpdates)
 	k.ForceRegisterMagicDNSIPv4Only.Store(forceRegisterMagicDNSIPv4Only)
-
-	// If both attributes are present, then "enable" should win.  This reflects
-	// the history of seamless key renewal.
-	//
-	// Before 1.90, seamless was a private alpha, opt-in feature.  Devices would
-	// only seamless do if customers opted in using the seamless renewal attr.
-	//
-	// In 1.90 and later, seamless is the default behaviour, and devices will use
-	// seamless unless explicitly told not to by control (e.g. if we discover
-	// a bug and want clients to use the prior behaviour).
-	//
-	// If a customer has opted in to the pre-1.90 seamless implementation, we
-	// don't want to switch it off for them -- we only want to switch it off for
-	// devices that haven't opted in.
-	k.SeamlessKeyRenewal.Store(seamlessKeyRenewal || !disableSeamlessKeyRenewal)
 }
 
 // AsDebugJSON returns k as something that can be marshalled with json.Marshal

ipn/ipnlocal/local.go

@@ -3571,12 +3571,11 @@ func (b *LocalBackend) setAuthURLLocked(url string) {
 //
 // b.mu must be held.
 func (b *LocalBackend) popBrowserAuthNowLocked(url string, keyExpired bool, recipient ipnauth.Actor) {
-	b.logf("popBrowserAuthNow(%q): url=%v, key-expired=%v, seamless-key-renewal=%v", maybeUsernameOf(recipient), url != "", keyExpired, b.seamlessRenewalEnabled())
+	b.logf("popBrowserAuthNow(%q): url=%v, key-expired=%v", maybeUsernameOf(recipient), url != "", keyExpired)
 
-	// Deconfigure the local network data plane if:
-	// - seamless key renewal is not enabled;
-	// - key is expired (in which case tailnet connectivity is down anyway).
-	if !b.seamlessRenewalEnabled() || keyExpired {
+	// Deconfigure the local network data plane if the key is expired
+	// (in which case tailnet connectivity is down anyway).
+	if keyExpired {
 		b.blockEngineUpdatesLocked(true)
 		b.stopEngineAndWaitLocked()
 
@@ -5938,9 +5937,9 @@ func (b *LocalBackend) enterStateLocked(newState ipn.State) {
 	switch newState {
 	case ipn.NeedsLogin:
 		feature.SystemdStatus("Needs login: %s", authURL)
-		// always block updates on NeedsLogin even if seamless renewal is enabled,
-		// to prevent calls to authReconfigLocked from reconfiguring the engine when our
-		// key has expired and we're waiting to authenticate to use the new key.
+		// always block updates on NeedsLogin, to prevent calls to authReconfigLocked
+		// from reconfiguring the engine when our key has expired and we're waiting
+		// to authenticate to use the new key.
 		b.blockEngineUpdatesLocked(true)
 		fallthrough
 	case ipn.Stopped, ipn.NoState:
@@ -7598,14 +7597,6 @@ func (b *LocalBackend) ReadRouteInfo() (*appctype.RouteInfo, error) {
 	return b.readRouteInfoLocked()
 }
 
-// seamlessRenewalEnabled reports whether seamless key renewals are enabled.
-//
-// As of 2025-09-11, this is the default behaviour unless nodes receive
-// [tailcfg.NodeAttrDisableSeamlessKeyRenewal] in their netmap.
-func (b *LocalBackend) seamlessRenewalEnabled() bool {
-	return b.ControlKnobs().SeamlessKeyRenewal.Load()
-}
-
 var (
 	disallowedAddrs = []netip.Addr{
 		netip.MustParseAddr("::1"),

ipn/ipnlocal/state_test.go

@@ -373,14 +373,6 @@ func (b *LocalBackend) nonInteractiveLoginForStateTest() {
 // predictable, but maybe a bit less thorough. This is more of an overall
 // state machine test than a test of the wgengine+magicsock integration.
 func TestStateMachine(t *testing.T) {
-	runTestStateMachine(t, false)
-}
-
-func TestStateMachineSeamless(t *testing.T) {
-	runTestStateMachine(t, true)
-}
-
-func runTestStateMachine(t *testing.T, seamless bool) {
 	envknob.Setenv("TAILSCALE_USE_WIP_CODE", "1")
 	defer envknob.Setenv("TAILSCALE_USE_WIP_CODE", "")
 	c := qt.New(t)
@@ -590,12 +582,6 @@ func runTestStateMachine(t *testing.T, seamless bool) {
 	cc.persist.UserProfile.LoginName = "user1"
 	cc.persist.NodeID = "node1"
 
-	// even if seamless is being enabled by default rather than by policy, this is
-	// the point where it will first get enabled.
-	if seamless {
-		sys.ControlKnobs().SeamlessKeyRenewal.Store(true)
-	}
-
 	cc.send(sendOpt{loginFinished: true, nm: &netmap.NetworkMap{}})
 	{
 		nn := notifies.drain(3)
@@ -1480,11 +1466,23 @@ func TestEngineReconfigOnStateChange(t *testing.T) {
 				lb.StartLoginInteractive(context.Background())
 				cc().sendAuthURL(node1)
 			},
-			// Without seamless renewal, even starting a reauth tears down everything:
-			wantState:     ipn.Starting,
-			wantCfg:       &wgcfg.Config{},
-			wantRouterCfg: &router.Config{},
-			wantDNSCfg:    &dns.Config{},
+			// Starting a reauth should leave everything up:
+			wantState: ipn.Starting,
+			wantCfg: &wgcfg.Config{
+				Peers:     []wgcfg.Peer{},
+				Addresses: node1.SelfNode.Addresses().AsSlice(),
+			},
+			wantRouterCfg: &router.Config{
+				SNATSubnetRoutes: true,
+				NetfilterMode:    preftype.NetfilterOn,
+				LocalAddrs:       node1.SelfNode.Addresses().AsSlice(),
+				Routes:           routesWithQuad100(),
+			},
+			wantDNSCfg: &dns.Config{
+				AcceptDNS: true,
+				Routes:    map[dnsname.FQDN][]*dnstype.Resolver{},
+				Hosts:     hostsFor(node1),
+			},
 		},
 		{
 			name: "Start/Connect/Login/InitReauth/Login",
@@ -1518,71 +1516,8 @@ func TestEngineReconfigOnStateChange(t *testing.T) {
 			},
 		},
 		{
-			name: "Seamless/Start/Connect/Login/InitReauth",
+			name: "Start/Connect/Login/Expire",
 			steps: func(t *testing.T, lb *LocalBackend, cc func() *mockControl) {
-				lb.ControlKnobs().SeamlessKeyRenewal.Store(true)
-				mustDo(t)(lb.Start(ipn.Options{}))
-				mustDo2(t)(lb.EditPrefs(connect))
-				cc().authenticated(node1)
-
-				// Start the re-auth process:
-				lb.StartLoginInteractive(context.Background())
-				cc().sendAuthURL(node1)
-			},
-			// With seamless renewal, starting a reauth should leave everything up:
-			wantState: ipn.Starting,
-			wantCfg: &wgcfg.Config{
-				Peers:     []wgcfg.Peer{},
-				Addresses: node1.SelfNode.Addresses().AsSlice(),
-			},
-			wantRouterCfg: &router.Config{
-				SNATSubnetRoutes: true,
-				NetfilterMode:    preftype.NetfilterOn,
-				LocalAddrs:       node1.SelfNode.Addresses().AsSlice(),
-				Routes:           routesWithQuad100(),
-			},
-			wantDNSCfg: &dns.Config{
-				AcceptDNS: true,
-				Routes:    map[dnsname.FQDN][]*dnstype.Resolver{},
-				Hosts:     hostsFor(node1),
-			},
-		},
-		{
-			name: "Seamless/Start/Connect/Login/InitReauth/Login",
-			steps: func(t *testing.T, lb *LocalBackend, cc func() *mockControl) {
-				lb.ControlKnobs().SeamlessKeyRenewal.Store(true)
-				mustDo(t)(lb.Start(ipn.Options{}))
-				mustDo2(t)(lb.EditPrefs(connect))
-				cc().authenticated(node1)
-
-				// Start the re-auth process:
-				lb.StartLoginInteractive(context.Background())
-				cc().sendAuthURL(node1)
-
-				// Complete the re-auth process:
-				cc().authenticated(node1)
-			},
-			wantState: ipn.Starting,
-			wantCfg: &wgcfg.Config{
-				Peers:     []wgcfg.Peer{},
-				Addresses: node1.SelfNode.Addresses().AsSlice(),
-			},
-			wantRouterCfg: &router.Config{
-				SNATSubnetRoutes: true,
-				NetfilterMode:    preftype.NetfilterOn,
-				LocalAddrs:       node1.SelfNode.Addresses().AsSlice(),
-				Routes:           routesWithQuad100(),
-			},
-			wantDNSCfg: &dns.Config{
-				AcceptDNS: true,
-				Routes:    map[dnsname.FQDN][]*dnstype.Resolver{},
-				Hosts:     hostsFor(node1),
-			},
-		},
-		{
-			name: "Seamless/Start/Connect/Login/Expire",
-			steps: func(t *testing.T, lb *LocalBackend, cc func() *mockControl) {
-				lb.ControlKnobs().SeamlessKeyRenewal.Store(true)
 				mustDo(t)(lb.Start(ipn.Options{}))
 				mustDo2(t)(lb.EditPrefs(connect))
 				cc().authenticated(node1)
@@ -1592,7 +1527,7 @@ func TestEngineReconfigOnStateChange(t *testing.T) {
 					}).View(),
 				}})
 			},
-			// Even with seamless, if the key we are using expires, we want to disconnect:
+			// If the key we are using expires, we want to disconnect:
 			wantState:     ipn.NeedsLogin,
 			wantCfg:       &wgcfg.Config{},
 			wantRouterCfg: &router.Config{},
@@ -1641,14 +1576,6 @@ func TestEngineReconfigOnStateChange(t *testing.T) {
 // TestSendPreservesAuthURL tests that wgengine updates arriving in the middle of
 // processing an auth URL doesn't result in the auth URL being cleared.
 func TestSendPreservesAuthURL(t *testing.T) {
-	runTestSendPreservesAuthURL(t, false)
-}
-
-func TestSendPreservesAuthURLSeamless(t *testing.T) {
-	runTestSendPreservesAuthURL(t, true)
-}
-
-func runTestSendPreservesAuthURL(t *testing.T, seamless bool) {
 	var cc *mockControl
 	b := newLocalBackendWithTestControl(t, true, func(tb testing.TB, opts controlclient.Options) controlclient.Client {
 		cc = newClient(t, opts)
@@ -1667,10 +1594,6 @@ func runTestSendPreservesAuthURL(t *testing.T, seamless bool) {
 	cc.persist.UserProfile.LoginName = "user1"
 	cc.persist.NodeID = "node1"
 
-	if seamless {
-		b.sys.ControlKnobs().SeamlessKeyRenewal.Store(true)
-	}
-
 	cc.send(sendOpt{loginFinished: true, nm: &netmap.NetworkMap{
 		SelfNode: (&tailcfg.Node{MachineAuthorized: true}).View(),
 	}})

tailcfg/tailcfg.go

@@ -2600,21 +2600,6 @@ const (
 	// This cannot be set simultaneously with NodeAttrLinuxMustUseIPTables.
 	NodeAttrLinuxMustUseNfTables NodeCapability = "linux-netfilter?v=nftables"
 
-	// NodeAttrDisableSeamlessKeyRenewal disables seamless key renewal, which is
-	// enabled by default in clients as of 2025-09-17 (1.90 and later).
-	//
-	// We will use this attribute to manage the rollout, and disable seamless in
-	// clients with known bugs.
-	// http://go/seamless-key-renewal
-	NodeAttrDisableSeamlessKeyRenewal NodeCapability = "disable-seamless-key-renewal"
-
-	// NodeAttrSeamlessKeyRenewal was used to opt-in to seamless key renewal
-	// during its private alpha.
-	//
-	// Deprecated: NodeAttrSeamlessKeyRenewal is deprecated as of CapabilityVersion 126,
-	// because seamless key renewal is now enabled by default.
-	NodeAttrSeamlessKeyRenewal NodeCapability = "seamless-key-renewal"
-
 	// NodeAttrProbeUDPLifetime makes the client probe UDP path lifetime at the
 	// tail end of an active direct connection in magicsock.
 	NodeAttrProbeUDPLifetime NodeCapability = "probe-udp-lifetime"

tstest/integration/integration_test.go

@@ -467,83 +467,70 @@ func TestOneNodeUpAuth(t *testing.T) {
 		},
 	} {
 		tstest.Shard(t)
+		t.Run(tt.name, func(t *testing.T) {
+			tstest.Parallel(t)
 
-		for _, useSeamlessKeyRenewal := range []bool{true, false} {
-			name := tt.name
-			if useSeamlessKeyRenewal {
-				name += "-with-seamless"
-			}
-			t.Run(name, func(t *testing.T) {
-				tstest.Parallel(t)
-
-				env := NewTestEnv(t, ConfigureControl(
-					func(control *testcontrol.Server) {
-						if tt.authKey != "" {
-							control.RequireAuthKey = tt.authKey
-						} else {
-							control.RequireAuth = true
-						}
-
-						if tt.requireDeviceApproval {
-							control.RequireMachineAuth = true
-						}
-
-						control.AllNodesSameUser = true
-
-						if useSeamlessKeyRenewal {
-							control.DefaultNodeCapabilities = &tailcfg.NodeCapMap{
-								tailcfg.NodeAttrSeamlessKeyRenewal: []tailcfg.RawMessage{},
-							}
-						}
-					},
-				))
-
-				n1 := NewTestNode(t, env)
-				d1 := n1.StartDaemon()
-				defer d1.MustCleanShutdown(t)
-
-				for i, step := range tt.steps {
-					t.Logf("Running step %d", i)
-					cmdArgs := append(step.args, "--login-server="+env.ControlURL())
-
-					t.Logf("Running command: %s", strings.Join(cmdArgs, " "))
-
-					var authURLCount atomic.Int32
-					var deviceApprovalURLCount atomic.Int32
-
-					handler := &authURLParserWriter{t: t,
-						authURLFn:           completeLogin(t, env.Control, &authURLCount),
-						deviceApprovalURLFn: completeDeviceApproval(t, n1, &deviceApprovalURLCount),
+			env := NewTestEnv(t, ConfigureControl(
+				func(control *testcontrol.Server) {
+					if tt.authKey != "" {
+						control.RequireAuthKey = tt.authKey
+					} else {
+						control.RequireAuth = true
 					}
 
-					cmd := n1.Tailscale(cmdArgs...)
-					cmd.Stdout = handler
-					cmd.Stdout = handler
-					cmd.Stderr = cmd.Stdout
-					if err := cmd.Run(); err != nil {
-						t.Fatalf("up: %v", err)
+					if tt.requireDeviceApproval {
+						control.RequireMachineAuth = true
 					}
 
-					n1.AwaitRunning()
+					control.AllNodesSameUser = true
+				},
+			))
 
-					var wantAuthURLCount int32
-					if step.wantAuthURL {
-						wantAuthURLCount = 1
-					}
-					if n := authURLCount.Load(); n != wantAuthURLCount {
-						t.Errorf("Auth URLs completed = %d; want %d", n, wantAuthURLCount)
-					}
+			n1 := NewTestNode(t, env)
+			d1 := n1.StartDaemon()
+			defer d1.MustCleanShutdown(t)
 
-					var wantDeviceApprovalURLCount int32
-					if step.wantDeviceApprovalURL {
-						wantDeviceApprovalURLCount = 1
-					}
-					if n := deviceApprovalURLCount.Load(); n != wantDeviceApprovalURLCount {
-						t.Errorf("Device approval URLs completed = %d; want %d", n, wantDeviceApprovalURLCount)
-					}
+			for i, step := range tt.steps {
+				t.Logf("Running step %d", i)
+				cmdArgs := append(step.args, "--login-server="+env.ControlURL())
+
+				t.Logf("Running command: %s", strings.Join(cmdArgs, " "))
+
+				var authURLCount atomic.Int32
+				var deviceApprovalURLCount atomic.Int32
+
+				handler := &authURLParserWriter{t: t,
+					authURLFn:           completeLogin(t, env.Control, &authURLCount),
+					deviceApprovalURLFn: completeDeviceApproval(t, n1, &deviceApprovalURLCount),
 				}
-			})
-		}
+
+				cmd := n1.Tailscale(cmdArgs...)
+				cmd.Stdout = handler
+				cmd.Stdout = handler
+				cmd.Stderr = cmd.Stdout
+				if err := cmd.Run(); err != nil {
+					t.Fatalf("up: %v", err)
+				}
+
+				n1.AwaitRunning()
+
+				var wantAuthURLCount int32
+				if step.wantAuthURL {
+					wantAuthURLCount = 1
+				}
+				if n := authURLCount.Load(); n != wantAuthURLCount {
+					t.Errorf("Auth URLs completed = %d; want %d", n, wantAuthURLCount)
+				}
+
+				var wantDeviceApprovalURLCount int32
+				if step.wantDeviceApprovalURL {
+					wantDeviceApprovalURLCount = 1
+				}
+				if n := deviceApprovalURLCount.Load(); n != wantDeviceApprovalURLCount {
+					t.Errorf("Device approval URLs completed = %d; want %d", n, wantDeviceApprovalURLCount)
+				}
+			}
+		})
 	}
 }