feat/fix: enhance cert-manager integration for metrics endpoints (follow-up to PR kubernetes-sigs#4243)

feat/fix: enhance cert-manager integration for metrics endpoints

This commit is a follow-up to PR kubernetes-sigs#4243, which introduced support for using cert-manager certificates for securing the metrics endpoint and ServiceMonitor. Related to kubernetes-sigs#3871 and kubernetes-sigs#4003

Key enhancements:
- Added support for configuring certificate integration via a Kustomize patch.
- Introduced configurable flags for greater flexibility in customization.
- Use Certwatcher to allow certificate rotation

This configuration provides an option for users to be production-ready.

These improvements enhance usability and adaptability while maintaining compatibility with the initial implementation. As the feature has not yet been released, this update ensures a polished and user-friendly integration for upcoming releases.

Author: camilamacedo86

.github/workflows/test-e2e-samples.yml

@@ -41,9 +41,10 @@ jobs:
         run: |
           KUSTOMIZATION_FILE_PATH="testdata/project-v4/config/default/kustomization.yaml"
           sed -i '25s/^#//' $KUSTOMIZATION_FILE_PATH
+          sed -i '47,49s/^#//' $KUSTOMIZATION_FILE_PATH
           # Uncomment all cert-manager injections
-          sed -i '57,170s/^#//' $KUSTOMIZATION_FILE_PATH
-          sed -i '172,187s/^#//' $KUSTOMIZATION_FILE_PATH
+          sed -i '59,212s/^#//' $KUSTOMIZATION_FILE_PATH
+          sed -i '214,229s/^#//' $KUSTOMIZATION_FILE_PATH
           cd testdata/project-v4/
           go mod tidy
 
@@ -85,10 +86,10 @@ jobs:
           # Uncomment only ValidatingWebhookConfiguration
           # from cert-manager replaces; we are leaving defaulting uncommented
           # since this sample has no defaulting webhooks
-          sed -i '57,123s/^#//' $KUSTOMIZATION_FILE_PATH
+          sed -i '59,164s/^#//' $KUSTOMIZATION_FILE_PATH
           # Uncomment only --conversion webhooks CA injection
-          sed -i '155,170s/^#//' $KUSTOMIZATION_FILE_PATH
-          sed -i '172,187s/^#//' $KUSTOMIZATION_FILE_PATH
+          sed -i '197,212s/^#//' $KUSTOMIZATION_FILE_PATH
+          sed -i '214,229s/^#//' $KUSTOMIZATION_FILE_PATH
           cd testdata/project-v4-with-plugins/
           go mod tidy
 
@@ -127,9 +128,10 @@ jobs:
         run: |
           KUSTOMIZATION_FILE_PATH="testdata/project-v4-multigroup/config/default/kustomization.yaml"
           sed -i '25s/^#//' $KUSTOMIZATION_FILE_PATH
-          # Uncomment all cert-manager injections
-          sed -i '57,170s/^#//' $KUSTOMIZATION_FILE_PATH
-          sed -i '172,187s/^#//' $KUSTOMIZATION_FILE_PATH
+          # Uncomment all cert-manager injections for webhooks only
+          sed -i '59,59s/^#//' $KUSTOMIZATION_FILE_PATH
+          sed -i '98,212s/^#//' $KUSTOMIZATION_FILE_PATH
+          sed -i '214,229s/^#//' $KUSTOMIZATION_FILE_PATH
           cd testdata/project-v4-multigroup
           go mod tidy
 

docs/book/src/cronjob-tutorial/testdata/project/cmd/main.go

@@ -76,6 +76,7 @@ func main() {
 	/*
 	 */
 	var metricsAddr string
+	var metricsCertPath, metricsCertName, metricsCertKey string
 	var webhookCertPath, webhookCertName, webhookCertKey string
 	var enableLeaderElection bool
 	var probeAddr string
@@ -93,6 +94,9 @@ func main() {
 	flag.StringVar(&webhookCertPath, "webhook-cert-path", "", "The directory that contains the webhook certificate.")
 	flag.StringVar(&webhookCertName, "webhook-cert-name", "tls.crt", "The name of the webhook certificate file.")
 	flag.StringVar(&webhookCertKey, "webhook-cert-key", "tls.key", "The name of the webhook key file.")
+	flag.StringVar(&metricsCertPath, "metrics-cert-path", "", "The directory that contains the metrics server certificate.")
+	flag.StringVar(&metricsCertName, "metrics-cert-name", "tls.crt", "The name of the metrics server certificate file.")
+	flag.StringVar(&metricsCertKey, "metrics-cert-key", "tls.key", "The name of the metrics server key file.")
 	flag.BoolVar(&enableHTTP2, "enable-http2", false,
 		"If set, HTTP/2 will be enabled for the metrics and webhook servers")
 	opts := zap.Options{
@@ -118,8 +122,8 @@ func main() {
 		tlsOpts = append(tlsOpts, disableHTTP2)
 	}
 
-	// Create watchers for metrics certificates
-	var webhookCertWatcher *certwatcher.CertWatcher
+	// Create watchers for metrics and webhooks certificates
+	var metricsCertWatcher, webhookCertWatcher *certwatcher.CertWatcher
 
 	// Initial webhook TLS options
 	webhookTLSOpts := append([]func(*tls.Config){}, tlsOpts...)
@@ -163,17 +167,33 @@ func main() {
 		// can access the metrics endpoint. The RBAC are configured in 'config/rbac/kustomization.yaml'. More info:
 		// https://pkg.go.dev/sigs.k8s.io/[email protected]/pkg/metrics/filters#WithAuthenticationAndAuthorization
 		metricsServerOptions.FilterProvider = filters.WithAuthenticationAndAuthorization
+	}
 
-		// TODO(user): If CertDir, CertName, and KeyName are not specified, controller-runtime will automatically
-		// generate self-signed certificates for the metrics server. While convenient for development and testing,
-		// this setup is not recommended for production.
+	// If the certificate is not specified, controller-runtime will automatically
+	// generate self-signed certificates for the metrics server. While convenient for development and testing,
+	// this setup is not recommended for production.
+	//
+	// TODO(user): If you enable certManager, uncomment the following lines:
+	// - [METRICS-WITH-CERTS] at config/default/kustomization.yaml to generate and use certificates
+	// managed by cert-manager for the metrics server.
+	// - [PROMETHEUS-WITH-CERTS] at config/prometheus/kustomization.yaml for TLS certification.
+	if len(metricsCertPath) > 0 {
+		setupLog.Info("Initializing metrics certificate watcher using provided certificates",
+			"metrics-cert-path", metricsCertPath, "metrics-cert-name", metricsCertName, "metrics-cert-key", metricsCertKey)
 
-		// TODO(user): If cert-manager is enabled in config/default/kustomization.yaml,
-		// you can uncomment the following lines to use the certificate managed by cert-manager.
-		// metricsServerOptions.CertDir = "/tmp/k8s-metrics-server/metrics-certs"
-		// metricsServerOptions.CertName = "tls.crt"
-		// metricsServerOptions.KeyName = "tls.key"
+		var err error
+		metricsCertWatcher, err = certwatcher.New(
+			filepath.Join(metricsCertPath, metricsCertName),
+			filepath.Join(metricsCertPath, metricsCertKey),
+		)
+		if err != nil {
+			setupLog.Error(err, "to initialize metrics certificate watcher", "error", err)
+			os.Exit(1)
+		}
 
+		metricsServerOptions.TLSOpts = append(metricsServerOptions.TLSOpts, func(config *tls.Config) {
+			config.GetCertificate = metricsCertWatcher.GetCertificate
+		})
 	}
 
 	mgr, err := ctrl.NewManager(ctrl.GetConfigOrDie(), ctrl.Options{
@@ -227,6 +247,14 @@ func main() {
 	}
 	// +kubebuilder:scaffold:builder
 
+	if metricsCertWatcher != nil {
+		setupLog.Info("Adding metrics certificate watcher to manager")
+		if err := mgr.Add(metricsCertWatcher); err != nil {
+			setupLog.Error(err, "unable to add metrics certificate watcher to manager")
+			os.Exit(1)
+		}
+	}
+
 	if webhookCertWatcher != nil {
 		setupLog.Info("Adding webhook certificate watcher to manager")
 		if err := mgr.Add(webhookCertWatcher); err != nil {

docs/book/src/cronjob-tutorial/testdata/project/config/certmanager/certificate-metrics.yaml

@@ -0,0 +1,20 @@
+# The following manifests contain a self-signed issuer CR and a metrics certificate CR.
+# More document can be found at https://docs.cert-manager.io
+apiVersion: cert-manager.io/v1
+kind: Certificate
+metadata:
+  labels:
+    app.kubernetes.io/name: project
+    app.kubernetes.io/managed-by: kustomize
+  name: metrics-certs  # this name should match the one appeared in kustomizeconfig.yaml
+  namespace: system
+spec:
+  dnsNames:
+  # SERVICE_NAME and SERVICE_NAMESPACE will be substituted by kustomize
+  # replacements in the config/default/kustomization.yaml file.
+  - SERVICE_NAME.SERVICE_NAMESPACE.svc
+  - SERVICE_NAME.SERVICE_NAMESPACE.svc.cluster.local
+  issuerRef:
+    kind: Issuer
+    name: selfsigned-issuer
+  secretName: metrics-server-cert 

docs/book/src/cronjob-tutorial/testdata/project/config/certmanager/certificate-webhook.yaml

@@ -0,0 +1,20 @@
+# The following manifests contain a self-signed issuer CR and a certificate CR.
+# More document can be found at https://docs.cert-manager.io
+apiVersion: cert-manager.io/v1
+kind: Certificate
+metadata:
+  labels:
+    app.kubernetes.io/name: project
+    app.kubernetes.io/managed-by: kustomize
+  name: serving-cert  # this name should match the one appeared in kustomizeconfig.yaml
+  namespace: system
+spec:
+  # SERVICE_NAME and SERVICE_NAMESPACE will be substituted by kustomize
+  # replacements in the config/default/kustomization.yaml file.
+  dnsNames:
+  - SERVICE_NAME.SERVICE_NAMESPACE.svc
+  - SERVICE_NAME.SERVICE_NAMESPACE.svc.cluster.local
+  issuerRef:
+    kind: Issuer
+    name: selfsigned-issuer
+  secretName: webhook-server-cert 

docs/book/src/cronjob-tutorial/testdata/project/config/certmanager/certificate.yaml

@@ -0,0 +1,13 @@
+# The following manifest contains a self-signed issuer CR.
+# More information can be found at https://docs.cert-manager.io
+# WARNING: Targets CertManager v1.0. Check https://cert-manager.io/docs/installation/upgrading/ for breaking changes.
+apiVersion: cert-manager.io/v1
+kind: Issuer
+metadata:
+  labels:
+    app.kubernetes.io/name: project
+    app.kubernetes.io/managed-by: kustomize
+  name: selfsigned-issuer
+  namespace: system
+spec:
+  selfSigned: {}

docs/book/src/cronjob-tutorial/testdata/project/config/certmanager/issuer.yaml

@@ -1,5 +1,7 @@
 resources:
-- certificate.yaml
+- issuer.yaml
+- certificate-webhook.yaml
+- certificate-metrics.yaml
 
 configurations:
 - kustomizeconfig.yaml

docs/book/src/cronjob-tutorial/testdata/project/config/certmanager/kustomization.yaml

@@ -0,0 +1,31 @@
+# This patch adds the args and volumes to allow the manager to use the metrics-server certs
+# Ensure the volumeMounts field exists by creating it if missing
+- op: add
+  path: /spec/template/spec/containers/0/volumeMounts
+  value: []
+- op: add
+  path: /spec/template/spec/containers/0/volumeMounts/-
+  value:
+    mountPath: /tmp/k8s-metrics-server/metrics-certs
+    name: metrics-certs
+    readOnly: true
+- op: add
+  path: /spec/template/spec/containers/0/args/-
+  value: --metrics-cert-path=/tmp/k8s-metrics-server/metrics-certs
+- op: add
+  path: /spec/template/spec/volumes
+  value: []
+- op: add
+  path: /spec/template/spec/volumes/-
+  value:
+    name: metrics-certs
+    secret:
+      secretName: metrics-server-cert
+      optional: false
+      items:
+        - key: ca.crt
+          path: ca.crt
+        - key: tls.crt
+          path: tls.crt
+        - key: tls.key
+          path: tls.key