cmd/containerboot: manage HA Ingress TLS certs from containerboot (#15303)

cmd/containerboot: manage HA Ingress TLS certs from containerboot

When ran as HA Ingress node, containerboot now can determine
whether it should manage TLS certs for the HA Ingress replicas
and call the LocalAPI cert endpoint to ensure initial issuance
and renewal of the shared TLS certs.

Updates tailscale/corp#24795

Signed-off-by: Irbe Krumina <irbe@tailscale.com>

cmd/containerboot/certs.go

@@ -0,0 +1,147 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build linux
+
+package main
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"net"
+	"sync"
+	"time"
+
+	"tailscale.com/ipn"
+	"tailscale.com/util/goroutines"
+	"tailscale.com/util/mak"
+)
+
+// certManager is responsible for issuing certificates for known domains and for
+// maintaining a loop that re-attempts issuance daily.
+// Currently cert manager logic is only run on ingress ProxyGroup replicas that are responsible for managing certs for
+// HA Ingress HTTPS endpoints ('write' replicas).
+type certManager struct {
+	lc      localClient
+	tracker goroutines.Tracker // tracks running goroutines
+	mu      sync.Mutex         // guards the following
+	// certLoops contains a map of DNS names, for which we currently need to
+	// manage certs to cancel functions that allow stopping a goroutine when
+	// we no longer need to manage certs for the DNS name.
+	certLoops map[string]context.CancelFunc
+}
+
+// ensureCertLoops ensures that, for all currently managed Service HTTPS
+// endpoints, there is a cert loop responsible for issuing and ensuring the
+// renewal of the TLS certs.
+// ServeConfig must not be nil.
+func (cm *certManager) ensureCertLoops(ctx context.Context, sc *ipn.ServeConfig) error {
+	if sc == nil {
+		return fmt.Errorf("[unexpected] ensureCertLoops called with nil ServeConfig")
+	}
+	currentDomains := make(map[string]bool)
+	const httpsPort = "443"
+	for _, service := range sc.Services {
+		for hostPort := range service.Web {
+			domain, port, err := net.SplitHostPort(string(hostPort))
+			if err != nil {
+				return fmt.Errorf("[unexpected] unable to parse HostPort %s", hostPort)
+			}
+			if port != httpsPort { // HA Ingress' HTTP endpoint
+				continue
+			}
+			currentDomains[domain] = true
+		}
+	}
+	cm.mu.Lock()
+	defer cm.mu.Unlock()
+	for domain := range currentDomains {
+		if _, exists := cm.certLoops[domain]; !exists {
+			cancelCtx, cancel := context.WithCancel(ctx)
+			mak.Set(&cm.certLoops, domain, cancel)
+			cm.tracker.Go(func() { cm.runCertLoop(cancelCtx, domain) })
+		}
+	}
+
+	// Stop goroutines for domain names that are no longer in the config.
+	for domain, cancel := range cm.certLoops {
+		if !currentDomains[domain] {
+			cancel()
+			delete(cm.certLoops, domain)
+		}
+	}
+	return nil
+}
+
+// runCertLoop:
+// - calls localAPI certificate endpoint to ensure that certs are issued for the
+// given domain name
+// - calls localAPI certificate endpoint daily to ensure that certs are renewed
+// - if certificate issuance failed retries after an exponential backoff period
+// starting at 1 minute and capped at 24 hours. Reset the backoff once issuance succeeds.
+// Note that renewal check also happens when the node receives an HTTPS request and it is possible that certs get
+// renewed at that point. Renewal here is needed to prevent the shared certs from expiry in edge cases where the 'write'
+// replica does not get any HTTPS requests.
+// https://letsencrypt.org/docs/integration-guide/#retrying-failures
+func (cm *certManager) runCertLoop(ctx context.Context, domain string) {
+	const (
+		normalInterval   = 24 * time.Hour  // regular renewal check
+		initialRetry     = 1 * time.Minute // initial backoff after a failure
+		maxRetryInterval = 24 * time.Hour  // max backoff period
+	)
+	timer := time.NewTimer(0) // fire off timer immediately
+	defer timer.Stop()
+	retryCount := 0
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-timer.C:
+			// We call the certificate endpoint, but don't do anything
+			// with the returned certs here.
+			// The call to the certificate endpoint will ensure that
+			// certs are issued/renewed as needed and stored in the
+			// relevant state store. For example, for HA Ingress
+			// 'write' replica, the cert and key will be stored in a
+			// Kubernetes Secret named after the domain for which we
+			// are issuing.
+			// Note that renewals triggered by the call to the
+			// certificates endpoint here and by renewal check
+			// triggered during a call to node's HTTPS endpoint
+			// share the same state/renewal lock mechanism, so we
+			// should not run into redundant issuances during
+			// concurrent renewal checks.
+			// TODO(irbekrm): maybe it is worth adding a new
+			// issuance endpoint that explicitly only triggers
+			// issuance and stores certs in the relevant store, but
+			// does not return certs to the caller?
+			_, _, err := cm.lc.CertPair(ctx, domain)
+			if err != nil {
+				log.Printf("error refreshing certificate for %s: %v", domain, err)
+			}
+			var nextInterval time.Duration
+			// TODO(irbekrm): distinguish between LE rate limit
+			// errors and other error types like transient network
+			// errors.
+			if err == nil {
+				retryCount = 0
+				nextInterval = normalInterval
+			} else {
+				retryCount++
+				// Calculate backoff: initialRetry * 2^(retryCount-1)
+				// For retryCount=1: 1min * 2^0 = 1min
+				// For retryCount=2: 1min * 2^1 = 2min
+				// For retryCount=3: 1min * 2^2 = 4min
+				backoff := initialRetry * time.Duration(1<<(retryCount-1))
+				if backoff > maxRetryInterval {
+					backoff = maxRetryInterval
+				}
+				nextInterval = backoff
+				log.Printf("Error refreshing certificate for %s (retry %d): %v. Will retry in %v\n",
+					domain, retryCount, err, nextInterval)
+			}
+			timer.Reset(nextInterval)
+		}
+	}
+}

cmd/containerboot/certs_test.go

@@ -0,0 +1,229 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build linux
+
+package main
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"tailscale.com/ipn"
+	"tailscale.com/tailcfg"
+)
+
+// TestEnsureCertLoops tests that the certManager correctly starts and stops
+// update loops for certs when the serve config changes. It tracks goroutine
+// count and uses that as a validator that the expected number of cert loops are
+// running.
+func TestEnsureCertLoops(t *testing.T) {
+	tests := []struct {
+		name              string
+		initialConfig     *ipn.ServeConfig
+		updatedConfig     *ipn.ServeConfig
+		initialGoroutines int64 // after initial serve config is applied
+		updatedGoroutines int64 // after updated serve config is applied
+		wantErr           bool
+	}{
+		{
+			name:              "empty_serve_config",
+			initialConfig:     &ipn.ServeConfig{},
+			initialGoroutines: 0,
+		},
+		{
+			name:              "nil_serve_config",
+			initialConfig:     nil,
+			initialGoroutines: 0,
+			wantErr:           true,
+		},
+		{
+			name:          "empty_to_one_service",
+			initialConfig: &ipn.ServeConfig{},
+			updatedConfig: &ipn.ServeConfig{
+				Services: map[tailcfg.ServiceName]*ipn.ServiceConfig{
+					"svc:my-app": {
+						Web: map[ipn.HostPort]*ipn.WebServerConfig{
+							"my-app.tailnetxyz.ts.net:443": {},
+						},
+					},
+				},
+			},
+			initialGoroutines: 0,
+			updatedGoroutines: 1,
+		},
+		{
+			name: "single_service",
+			initialConfig: &ipn.ServeConfig{
+				Services: map[tailcfg.ServiceName]*ipn.ServiceConfig{
+					"svc:my-app": {
+						Web: map[ipn.HostPort]*ipn.WebServerConfig{
+							"my-app.tailnetxyz.ts.net:443": {},
+						},
+					},
+				},
+			},
+			initialGoroutines: 1,
+		},
+		{
+			name: "multiple_services",
+			initialConfig: &ipn.ServeConfig{
+				Services: map[tailcfg.ServiceName]*ipn.ServiceConfig{
+					"svc:my-app": {
+						Web: map[ipn.HostPort]*ipn.WebServerConfig{
+							"my-app.tailnetxyz.ts.net:443": {},
+						},
+					},
+					"svc:my-other-app": {
+						Web: map[ipn.HostPort]*ipn.WebServerConfig{
+							"my-other-app.tailnetxyz.ts.net:443": {},
+						},
+					},
+				},
+			},
+			initialGoroutines: 2, // one loop per domain across all services
+		},
+		{
+			name: "ignore_non_https_ports",
+			initialConfig: &ipn.ServeConfig{
+				Services: map[tailcfg.ServiceName]*ipn.ServiceConfig{
+					"svc:my-app": {
+						Web: map[ipn.HostPort]*ipn.WebServerConfig{
+							"my-app.tailnetxyz.ts.net:443": {},
+							"my-app.tailnetxyz.ts.net:80":  {},
+						},
+					},
+				},
+			},
+			initialGoroutines: 1, // only one loop for the 443 endpoint
+		},
+		{
+			name: "remove_domain",
+			initialConfig: &ipn.ServeConfig{
+				Services: map[tailcfg.ServiceName]*ipn.ServiceConfig{
+					"svc:my-app": {
+						Web: map[ipn.HostPort]*ipn.WebServerConfig{
+							"my-app.tailnetxyz.ts.net:443": {},
+						},
+					},
+					"svc:my-other-app": {
+						Web: map[ipn.HostPort]*ipn.WebServerConfig{
+							"my-other-app.tailnetxyz.ts.net:443": {},
+						},
+					},
+				},
+			},
+			updatedConfig: &ipn.ServeConfig{
+				Services: map[tailcfg.ServiceName]*ipn.ServiceConfig{
+					"svc:my-app": {
+						Web: map[ipn.HostPort]*ipn.WebServerConfig{
+							"my-app.tailnetxyz.ts.net:443": {},
+						},
+					},
+				},
+			},
+			initialGoroutines: 2, // initially two loops (one per service)
+			updatedGoroutines: 1, // one loop after removing service2
+		},
+		{
+			name: "add_domain",
+			initialConfig: &ipn.ServeConfig{
+				Services: map[tailcfg.ServiceName]*ipn.ServiceConfig{
+					"svc:my-app": {
+						Web: map[ipn.HostPort]*ipn.WebServerConfig{
+							"my-app.tailnetxyz.ts.net:443": {},
+						},
+					},
+				},
+			},
+			updatedConfig: &ipn.ServeConfig{
+				Services: map[tailcfg.ServiceName]*ipn.ServiceConfig{
+					"svc:my-app": {
+						Web: map[ipn.HostPort]*ipn.WebServerConfig{
+							"my-app.tailnetxyz.ts.net:443": {},
+						},
+					},
+					"svc:my-other-app": {
+						Web: map[ipn.HostPort]*ipn.WebServerConfig{
+							"my-other-app.tailnetxyz.ts.net:443": {},
+						},
+					},
+				},
+			},
+			initialGoroutines: 1,
+			updatedGoroutines: 2,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			ctx, cancel := context.WithCancel(context.Background())
+			defer cancel()
+
+			cm := &certManager{
+				lc:        &fakeLocalClient{},
+				certLoops: make(map[string]context.CancelFunc),
+			}
+
+			allDone := make(chan bool, 1)
+			defer cm.tracker.AddDoneCallback(func() {
+				cm.mu.Lock()
+				defer cm.mu.Unlock()
+				if cm.tracker.RunningGoroutines() > 0 {
+					return
+				}
+				select {
+				case allDone <- true:
+				default:
+				}
+			})()
+
+			err := cm.ensureCertLoops(ctx, tt.initialConfig)
+			if (err != nil) != tt.wantErr {
+				t.Fatalf("ensureCertLoops() error = %v", err)
+			}
+
+			if got := cm.tracker.RunningGoroutines(); got != tt.initialGoroutines {
+				t.Errorf("after initial config: got %d running goroutines, want %d", got, tt.initialGoroutines)
+			}
+
+			if tt.updatedConfig != nil {
+				if err := cm.ensureCertLoops(ctx, tt.updatedConfig); err != nil {
+					t.Fatalf("ensureCertLoops() error on update = %v", err)
+				}
+
+				// Although starting goroutines and cancelling
+				// the context happens in the main goroutine, it
+				// the actual goroutine exit when a context is
+				// cancelled does not- so wait for a bit for the
+				// running goroutine count to reach the expected
+				// number.
+				deadline := time.After(5 * time.Second)
+				for {
+					if got := cm.tracker.RunningGoroutines(); got == tt.updatedGoroutines {
+						break
+					}
+					select {
+					case <-deadline:
+						t.Fatalf("timed out waiting for goroutine count to reach %d, currently at %d",
+							tt.updatedGoroutines, cm.tracker.RunningGoroutines())
+					case <-time.After(10 * time.Millisecond):
+						continue
+					}
+				}
+			}
+
+			if tt.updatedGoroutines == 0 {
+				return // no goroutines to wait for
+			}
+			// cancel context to make goroutines exit
+			cancel()
+			select {
+			case <-time.After(5 * time.Second):
+				t.Fatal("timed out waiting for goroutine to finish")
+			case <-allDone:
+			}
+		})
+	}
+}

cmd/containerboot/main.go

@@ -646,7 +646,7 @@ runLoop:
 
 				if cfg.ServeConfigPath != "" {
 					triggerWatchServeConfigChanges.Do(func() {
-						go watchServeConfigChanges(ctx, cfg.ServeConfigPath, certDomainChanged, certDomain, client, kc)
+						go watchServeConfigChanges(ctx, certDomainChanged, certDomain, client, kc, cfg)
 					})
 				}
 

cmd/containerboot/serve.go

@@ -28,10 +28,11 @@ import (
 // applies it to lc. It exits when ctx is canceled. cdChanged is a channel that
 // is written to when the certDomain changes, causing the serve config to be
 // re-read and applied.
-func watchServeConfigChanges(ctx context.Context, path string, cdChanged <-chan bool, certDomainAtomic *atomic.Pointer[string], lc *local.Client, kc *kubeClient) {
+func watchServeConfigChanges(ctx context.Context, cdChanged <-chan bool, certDomainAtomic *atomic.Pointer[string], lc *local.Client, kc *kubeClient, cfg *settings) {
 	if certDomainAtomic == nil {
 		panic("certDomainAtomic must not be nil")
 	}
+
 	var tickChan <-chan time.Time
 	var eventChan <-chan fsnotify.Event
 	if w, err := fsnotify.NewWatcher(); err != nil {
@@ -43,7 +44,7 @@ func watchServeConfigChanges(ctx context.Context, path string, cdChanged <-chan
 		tickChan = ticker.C
 	} else {
 		defer w.Close()
-		if err := w.Add(filepath.Dir(path)); err != nil {
+		if err := w.Add(filepath.Dir(cfg.ServeConfigPath)); err != nil {
 			log.Fatalf("serve proxy: failed to add fsnotify watch: %v", err)
 		}
 		eventChan = w.Events
@@ -51,6 +52,12 @@ func watchServeConfigChanges(ctx context.Context, path string, cdChanged <-chan
 
 	var certDomain string
 	var prevServeConfig *ipn.ServeConfig
+	var cm certManager
+	if cfg.CertShareMode == "rw" {
+		cm = certManager{
+			lc: lc,
+		}
+	}
 	for {
 		select {
 		case <-ctx.Done():
@@ -63,12 +70,12 @@ func watchServeConfigChanges(ctx context.Context, path string, cdChanged <-chan
 			// k8s handles these mounts. So just re-read the file and apply it
 			// if it's changed.
 		}
-		sc, err := readServeConfig(path, certDomain)
+		sc, err := readServeConfig(cfg.ServeConfigPath, certDomain)
 		if err != nil {
 			log.Fatalf("serve proxy: failed to read serve config: %v", err)
 		}
 		if sc == nil {
-			log.Printf("serve proxy: no serve config at %q, skipping", path)
+			log.Printf("serve proxy: no serve config at %q, skipping", cfg.ServeConfigPath)
 			continue
 		}
 		if prevServeConfig != nil && reflect.DeepEqual(sc, prevServeConfig) {
@@ -83,6 +90,12 @@ func watchServeConfigChanges(ctx context.Context, path string, cdChanged <-chan
 			}
 		}
 		prevServeConfig = sc
+		if cfg.CertShareMode != "rw" {
+			continue
+		}
+		if err := cm.ensureCertLoops(ctx, sc); err != nil {
+			log.Fatalf("serve proxy: error ensuring cert loops: %v", err)
+		}
 	}
 }
 
@@ -96,6 +109,7 @@ func certDomainFromNetmap(nm *netmap.NetworkMap) string {
 // localClient is a subset of [local.Client] that can be mocked for testing.
 type localClient interface {
 	SetServeConfig(context.Context, *ipn.ServeConfig) error
+	CertPair(context.Context, string) ([]byte, []byte, error)
 }
 
 func updateServeConfig(ctx context.Context, sc *ipn.ServeConfig, certDomain string, lc localClient) error {

cmd/containerboot/serve_test.go

@@ -206,6 +206,10 @@ func (m *fakeLocalClient) SetServeConfig(ctx context.Context, cfg *ipn.ServeConf
 	return nil
 }
 
+func (m *fakeLocalClient) CertPair(ctx context.Context, domain string) (certPEM, keyPEM []byte, err error) {
+	return nil, nil, nil
+}
+
 func TestHasHTTPSEndpoint(t *testing.T) {
 	tests := []struct {
 		name string

cmd/containerboot/settings.go

@@ -74,6 +74,12 @@ type settings struct {
 	HealthCheckEnabled   bool
 	DebugAddrPort        string
 	EgressProxiesCfgPath string
+	// CertShareMode is set for Kubernetes Pods running cert share mode.
+	// Possible values are empty (containerboot doesn't run any certs
+	// logic),  'ro' (for Pods that shold never attempt to issue/renew
+	// certs) and 'rw' for Pods that should manage the TLS certs shared
+	// amongst the replicas.
+	CertShareMode string
 }
 
 func configFromEnv() (*settings, error) {
@@ -128,6 +134,17 @@ func configFromEnv() (*settings, error) {
 			cfg.PodIPv6 = parsed.String()
 		}
 	}
+	// If cert share is enabled, set the replica as read or write. Only 0th
+	// replica should be able to write.
+	isInCertShareMode := defaultBool("TS_EXPERIMENTAL_CERT_SHARE", false)
+	if isInCertShareMode {
+		cfg.CertShareMode = "ro"
+		podName := os.Getenv("POD_NAME")
+		if strings.HasSuffix(podName, "-0") {
+			cfg.CertShareMode = "rw"
+		}
+	}
+
 	if err := cfg.validate(); err != nil {
 		return nil, fmt.Errorf("invalid configuration: %v", err)
 	}

cmd/containerboot/tailscaled.go

@@ -33,6 +33,9 @@ func startTailscaled(ctx context.Context, cfg *settings) (*local.Client, *os.Pro
 	cmd.SysProcAttr = &syscall.SysProcAttr{
 		Setpgid: true,
 	}
+	if cfg.CertShareMode != "" {
+		cmd.Env = append(os.Environ(), "TS_CERT_SHARE_MODE="+cfg.CertShareMode)
+	}
 	log.Printf("Starting tailscaled")
 	if err := cmd.Start(); err != nil {
 		return nil, nil, fmt.Errorf("starting tailscaled failed: %v", err)