🐛 Refactor certificate watcher to use polling, instead of fsnotify

examples/scratch-env/go.mod

@@ -14,7 +14,6 @@ require (
 	github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc // indirect
 	github.com/emicklei/go-restful/v3 v3.11.0 // indirect
 	github.com/evanphx/json-patch/v5 v5.9.0 // indirect
-	github.com/fsnotify/fsnotify v1.7.0 // indirect
 	github.com/fxamacker/cbor/v2 v2.7.0 // indirect
 	github.com/go-logr/logr v1.4.2 // indirect
 	github.com/go-logr/zapr v1.3.0 // indirect

examples/scratch-env/go.sum

@@ -13,8 +13,6 @@ github.com/evanphx/json-patch v0.5.2 h1:xVCHIVMUu1wtM/VkR9jVZ45N3FhZfYMMYGorLCR8
 github.com/evanphx/json-patch v0.5.2/go.mod h1:ZWS5hhDbVDyob71nXKNL0+PWn6ToqBHMikGIFbs31qQ=
 github.com/evanphx/json-patch/v5 v5.9.0 h1:kcBlZQbplgElYIlo/n1hJbls2z/1awpXxpRi0/FOJfg=
 github.com/evanphx/json-patch/v5 v5.9.0/go.mod h1:VNkHZ/282BpEyt/tObQO8s5CMPmYYq14uClGH4abBuQ=
-github.com/fsnotify/fsnotify v1.7.0 h1:8JEhPFa5W2WU7YfeZzPNqzMP6Lwt7L2715Ggo0nosvA=
-github.com/fsnotify/fsnotify v1.7.0/go.mod h1:40Bi/Hjc2AVfZrqy+aj+yEI+/bRxZnMJyTJwOpGvigM=
 github.com/fxamacker/cbor/v2 v2.7.0 h1:iM5WgngdRBanHcxugY4JySA0nk1wZorNOpTgCMedv5E=
 github.com/fxamacker/cbor/v2 v2.7.0/go.mod h1:pxXPTn3joSm21Gbwsv0w9OSA2y1HFR9qXEeXQVeNoDQ=
 github.com/go-logr/logr v1.4.2 h1:6pFjapn8bFcIbiKo3XT4j/BhANplGihG6tvd+8rYgrY=

go.mod

@@ -4,7 +4,6 @@ go 1.23.0
 
 require (
 	github.com/evanphx/json-patch/v5 v5.9.0
-	github.com/fsnotify/fsnotify v1.7.0
 	github.com/go-logr/logr v1.4.2
 	github.com/go-logr/zapr v1.3.0
 	github.com/google/go-cmp v0.6.0
@@ -41,6 +40,7 @@ require (
 	github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc // indirect
 	github.com/emicklei/go-restful/v3 v3.11.0 // indirect
 	github.com/felixge/httpsnoop v1.0.4 // indirect
+	github.com/fsnotify/fsnotify v1.7.0 // indirect
 	github.com/fxamacker/cbor/v2 v2.7.0 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
 	github.com/go-openapi/jsonpointer v0.21.0 // indirect

pkg/certwatcher/certwatcher.go

@@ -17,58 +17,55 @@ limitations under the License.
 package certwatcher
 
 import (
+	"bytes"
 	"context"
 	"crypto/tls"
-	"fmt"
+	"os"
 	"sync"
 	"time"
 
-	"github.com/fsnotify/fsnotify"
-	kerrors "k8s.io/apimachinery/pkg/util/errors"
-	"k8s.io/apimachinery/pkg/util/sets"
-	"k8s.io/apimachinery/pkg/util/wait"
 	"sigs.k8s.io/controller-runtime/pkg/certwatcher/metrics"
 	logf "sigs.k8s.io/controller-runtime/pkg/internal/log"
 )
 
 var log = logf.RuntimeLog.WithName("certwatcher")
 
-// CertWatcher watches certificate and key files for changes.  When either file
-// changes, it reads and parses both and calls an optional callback with the new
-// certificate.
+const defaultWatchInterval = 10 * time.Second
+
+// CertWatcher watches certificate and key files for changes.
+// It always returns the cached version,
+// but periodically reads and parses certificate and key for changes
+// and calls an optional callback with the new certificate.
 type CertWatcher struct {
 	sync.RWMutex
 
 	currentCert *tls.Certificate
-	watcher     *fsnotify.Watcher
+	interval    time.Duration
 
 	certPath string
 	keyPath  string
 
+	cachedKeyPEMBlock []byte
+
 	// callback is a function to be invoked when the certificate changes.
 	callback func(tls.Certificate)
 }
 
 // New returns a new CertWatcher watching the given certificate and key.
 func New(certPath, keyPath string) (*CertWatcher, error) {
-	var err error
-
 	cw := &CertWatcher{
 		certPath: certPath,
 		keyPath:  keyPath,
+		interval: defaultWatchInterval,
 	}
 
-	// Initial read of certificate and key.
-	if err := cw.ReadCertificate(); err != nil {
-		return nil, err
-	}
-
-	cw.watcher, err = fsnotify.NewWatcher()
-	if err != nil {
-		return nil, err
-	}
+	return cw, cw.ReadCertificate()
+}
 
-	return cw, nil
+// WithWatchInterval sets the watch interval and returns the CertWatcher pointer
+func (cw *CertWatcher) WithWatchInterval(interval time.Duration) *CertWatcher {
+	cw.interval = interval
+	return cw
 }
 
 // RegisterCallback registers a callback to be invoked when the certificate changes.
@@ -91,72 +88,64 @@ func (cw *CertWatcher) GetCertificate(_ *tls.ClientHelloInfo) (*tls.Certificate,
 
 // Start starts the watch on the certificate and key files.
 func (cw *CertWatcher) Start(ctx context.Context) error {
-	files := sets.New(cw.certPath, cw.keyPath)
-
-	{
-		var watchErr error
-		if err := wait.PollUntilContextTimeout(ctx, 1*time.Second, 10*time.Second, true, func(ctx context.Context) (done bool, err error) {
-			for _, f := range files.UnsortedList() {
-				if err := cw.watcher.Add(f); err != nil {
-					watchErr = err
-					return false, nil //nolint:nilerr // We want to keep trying.
-				}
-				// We've added the watch, remove it from the set.
-				files.Delete(f)
-			}
-			return true, nil
-		}); err != nil {
-			return fmt.Errorf("failed to add watches: %w", kerrors.NewAggregate([]error{err, watchErr}))
-		}
-	}
-
-	go cw.Watch()
+	ticker := time.NewTicker(cw.interval)
+	defer ticker.Stop()
 
 	log.Info("Starting certificate watcher")
-
-	// Block until the context is done.
-	<-ctx.Done()
-
-	return cw.watcher.Close()
-}
-
-// Watch reads events from the watcher's channel and reacts to changes.
-func (cw *CertWatcher) Watch() {
 	for {
 		select {
-		case event, ok := <-cw.watcher.Events:
-			// Channel is closed.
-			if !ok {
-				return
+		case <-ctx.Done():
+			return nil
+		case <-ticker.C:
+			if err := cw.ReadCertificate(); err != nil {
+				log.Error(err, "failed read certificate")
 			}
+		}
+	}
+}
 
-			cw.handleEvent(event)
-
-		case err, ok := <-cw.watcher.Errors:
-			// Channel is closed.
-			if !ok {
-				return
-			}
+// updateCachedCertificate checks if the new certificate differs from the cache,
+// updates it and returns the result if it was updated or not
+func (cw *CertWatcher) updateCachedCertificate(cert *tls.Certificate, keyPEMBlock []byte) bool {
+	cw.Lock()
+	defer cw.Unlock()
 
-			log.Error(err, "certificate watch error")
-		}
+	if cw.currentCert != nil &&
+		bytes.Equal(cw.currentCert.Certificate[0], cert.Certificate[0]) &&
+		bytes.Equal(cw.cachedKeyPEMBlock, keyPEMBlock) {
+		log.V(7).Info("certificate already cached")
+		return false
 	}
+	cw.currentCert = cert
+	cw.cachedKeyPEMBlock = keyPEMBlock
+	return true
 }
 
 // ReadCertificate reads the certificate and key files from disk, parses them,
-// and updates the current certificate on the watcher.  If a callback is set, it
+// and updates the current certificate on the watcher if updated. If a callback is set, it
 // is invoked with the new certificate.
 func (cw *CertWatcher) ReadCertificate() error {
 	metrics.ReadCertificateTotal.Inc()
-	cert, err := tls.LoadX509KeyPair(cw.certPath, cw.keyPath)
+	certPEMBlock, err := os.ReadFile(cw.certPath)
+	if err != nil {
+		metrics.ReadCertificateErrors.Inc()
+		return err
+	}
+	keyPEMBlock, err := os.ReadFile(cw.keyPath)
 	if err != nil {
 		metrics.ReadCertificateErrors.Inc()
 		return err
 	}
 
-	cw.Lock()
-	cw.currentCert = &cert
-	cw.Unlock()
+	cert, err := tls.X509KeyPair(certPEMBlock, keyPEMBlock)
+	if err != nil {
+		metrics.ReadCertificateErrors.Inc()
+		return err
+	}
+
+	if !cw.updateCachedCertificate(&cert, keyPEMBlock) {
+		return nil
+	}
 
 	log.Info("Updated current TLS certificate")
 
@@ -170,39 +159,3 @@ func (cw *CertWatcher) ReadCertificate() error {
 	}
 	return nil
 }
-
-func (cw *CertWatcher) handleEvent(event fsnotify.Event) {
-	// Only care about events which may modify the contents of the file.
-	if !(isWrite(event) || isRemove(event) || isCreate(event) || isChmod(event)) {
-		return
-	}
-
-	log.V(1).Info("certificate event", "event", event)
-
-	// If the file was removed or renamed, re-add the watch to the previous name
-	if isRemove(event) || isChmod(event) {
-		if err := cw.watcher.Add(event.Name); err != nil {
-			log.Error(err, "error re-watching file")
-		}
-	}
-
-	if err := cw.ReadCertificate(); err != nil {
-		log.Error(err, "error re-reading certificate")
-	}
-}
-
-func isWrite(event fsnotify.Event) bool {
-	return event.Op.Has(fsnotify.Write)
-}
-
-func isCreate(event fsnotify.Event) bool {
-	return event.Op.Has(fsnotify.Create)
-}
-
-func isRemove(event fsnotify.Event) bool {
-	return event.Op.Has(fsnotify.Remove)
-}
-
-func isChmod(event fsnotify.Event) bool {
-	return event.Op.Has(fsnotify.Chmod)
-}

pkg/certwatcher/certwatcher_suite_test.go

@@ -22,6 +22,7 @@ import (
 
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
+
 	logf "sigs.k8s.io/controller-runtime/pkg/log"
 	"sigs.k8s.io/controller-runtime/pkg/log/zap"
 )

pkg/certwatcher/certwatcher_test.go

@@ -34,6 +34,7 @@ import (
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
 	"github.com/prometheus/client_golang/prometheus/testutil"
+
 	"sigs.k8s.io/controller-runtime/pkg/certwatcher"
 	"sigs.k8s.io/controller-runtime/pkg/certwatcher/metrics"
 )
@@ -80,7 +81,7 @@ var _ = Describe("CertWatcher", func() {
 			go func() {
 				defer GinkgoRecover()
 				defer close(doneCh)
-				Expect(watcher.Start(ctx)).To(Succeed())
+				Expect(watcher.WithWatchInterval(time.Second).Start(ctx)).To(Succeed())
 			}()
 			// wait till we read first cert
 			Eventually(func() error {
@@ -113,7 +114,7 @@ var _ = Describe("CertWatcher", func() {
 			Eventually(func() bool {
 				secondcert, _ := watcher.GetCertificate(nil)
 				first := firstcert.PrivateKey.(*rsa.PrivateKey)
-				return first.Equal(secondcert.PrivateKey)
+				return first.Equal(secondcert.PrivateKey) || firstcert.Leaf.SerialNumber == secondcert.Leaf.SerialNumber
 			}).ShouldNot(BeTrue())
 
 			ctxCancel()
@@ -143,14 +144,41 @@ var _ = Describe("CertWatcher", func() {
 			Eventually(func() bool {
 				secondcert, _ := watcher.GetCertificate(nil)
 				first := firstcert.PrivateKey.(*rsa.PrivateKey)
-				return first.Equal(secondcert.PrivateKey)
+				return first.Equal(secondcert.PrivateKey) || firstcert.Leaf.SerialNumber == secondcert.Leaf.SerialNumber
 			}).ShouldNot(BeTrue())
 
 			ctxCancel()
 			Eventually(doneCh, "4s").Should(BeClosed())
 			Expect(called.Load()).To(BeNumerically(">=", 1))
 		})
 
+		It("should reload currentCert after move out", func() {
+			doneCh := startWatcher()
+			called := atomic.Int64{}
+			watcher.RegisterCallback(func(crt tls.Certificate) {
+				called.Add(1)
+				Expect(crt.Certificate).ToNot(BeEmpty())
+			})
+
+			firstcert, _ := watcher.GetCertificate(nil)
+
+			Expect(os.Rename(certPath, certPath+".old")).To(Succeed())
+			Expect(os.Rename(keyPath, keyPath+".old")).To(Succeed())
+
+			err := writeCerts(certPath, keyPath, "192.168.0.3")
+			Expect(err).ToNot(HaveOccurred())
+
+			Eventually(func() bool {
+				secondcert, _ := watcher.GetCertificate(nil)
+				first := firstcert.PrivateKey.(*rsa.PrivateKey)
+				return first.Equal(secondcert.PrivateKey) || firstcert.Leaf.SerialNumber == secondcert.Leaf.SerialNumber
+			}, "10s", "1s").ShouldNot(BeTrue())
+
+			ctxCancel()
+			Eventually(doneCh, "4s").Should(BeClosed())
+			Expect(called.Load()).To(BeNumerically(">=", 1))
+		})
+
 		Context("prometheus metric read_certificate_total", func() {
 			var readCertificateTotalBefore float64
 			var readCertificateErrorsBefore float64
@@ -165,8 +193,8 @@ var _ = Describe("CertWatcher", func() {
 
 				Eventually(func() error {
 					readCertificateTotalAfter := testutil.ToFloat64(metrics.ReadCertificateTotal)
-					if readCertificateTotalAfter != readCertificateTotalBefore+1.0 {
-						return fmt.Errorf("metric read certificate total expected: %v and got: %v", readCertificateTotalBefore+1.0, readCertificateTotalAfter)
+					if readCertificateTotalAfter < readCertificateTotalBefore+1.0 {
+						return fmt.Errorf("metric read certificate total expected at least: %v and got: %v", readCertificateTotalBefore+1.0, readCertificateTotalAfter)
 					}
 					return nil
 				}, "4s").Should(Succeed())
@@ -180,8 +208,8 @@ var _ = Describe("CertWatcher", func() {
 
 				Eventually(func() error {
 					readCertificateTotalAfter := testutil.ToFloat64(metrics.ReadCertificateTotal)
-					if readCertificateTotalAfter != readCertificateTotalBefore+1.0 {
-						return fmt.Errorf("metric read certificate total expected: %v and got: %v", readCertificateTotalBefore+1.0, readCertificateTotalAfter)
+					if readCertificateTotalAfter < readCertificateTotalBefore+1.0 {
+						return fmt.Errorf("metric read certificate total expected at least: %v and got: %v", readCertificateTotalBefore+1.0, readCertificateTotalAfter)
 					}
 					readCertificateTotalBefore = readCertificateTotalAfter
 					return nil
@@ -192,15 +220,15 @@ var _ = Describe("CertWatcher", func() {
 				// Note, we are checking two errors here, because os.Remove generates two fsnotify events: Chmod + Remove
 				Eventually(func() error {
 					readCertificateTotalAfter := testutil.ToFloat64(metrics.ReadCertificateTotal)
-					if readCertificateTotalAfter != readCertificateTotalBefore+2.0 {
-						return fmt.Errorf("metric read certificate total expected: %v and got: %v", readCertificateTotalBefore+2.0, readCertificateTotalAfter)
+					if readCertificateTotalAfter < readCertificateTotalBefore+2.0 {
+						return fmt.Errorf("metric read certificate total expected at least: %v and got: %v", readCertificateTotalBefore+2.0, readCertificateTotalAfter)
 					}
 					return nil
 				}, "4s").Should(Succeed())
 				Eventually(func() error {
 					readCertificateErrorsAfter := testutil.ToFloat64(metrics.ReadCertificateErrors)
-					if readCertificateErrorsAfter != readCertificateErrorsBefore+2.0 {
-						return fmt.Errorf("metric read certificate errors expected: %v and got: %v", readCertificateErrorsBefore+2.0, readCertificateErrorsAfter)
+					if readCertificateErrorsAfter < readCertificateErrorsBefore+2.0 {
+						return fmt.Errorf("metric read certificate errors expected at least: %v and got: %v", readCertificateErrorsBefore+2.0, readCertificateErrorsAfter)
 					}
 					return nil
 				}, "4s").Should(Succeed())

pkg/certwatcher/example_test.go

@@ -39,7 +39,7 @@ func Example() {
 		panic(err)
 	}
 
-	// Start goroutine with certwatcher running fsnotify against supplied certdir
+	// Start goroutine with certwatcher running against supplied cert
 	go func() {
 		if err := watcher.Start(ctx); err != nil {
 			panic(err)

pkg/certwatcher/metrics/metrics.go

@@ -18,6 +18,7 @@ package metrics
 
 import (
 	"github.com/prometheus/client_golang/prometheus"
+
 	"sigs.k8s.io/controller-runtime/pkg/metrics"
 )