kubelet: lazy enabling the ClusterTrustBundleProjection feature

Determine whether the ClusterTrustBundleProjection should be enabled
based on ClusterTrustBundle API discovery.
Some distributions may rely on a running kubelet in order to start
their kube-apiserver. Therefore we must delay the API discovery.

This patch delays it until the first time a clustertrustbundle is
requested from the InformerMaanager.

pkg/kubelet/clustertrustbundle/clustertrustbundle_manager.go

@@ -23,14 +23,18 @@ import (
 	"encoding/pem"
 	"fmt"
 	"math/rand"
+	"sync"
 	"time"
 
+	"github.com/go-logr/logr"
 	certificatesv1beta1 "k8s.io/api/certificates/v1beta1"
 	k8serrors "k8s.io/apimachinery/pkg/api/errors"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	lrucache "k8s.io/apimachinery/pkg/util/cache"
 	"k8s.io/apimachinery/pkg/util/sets"
+	"k8s.io/client-go/informers"
 	certinformersv1beta1 "k8s.io/client-go/informers/certificates/v1beta1"
+	clientset "k8s.io/client-go/kubernetes"
 	certlistersv1beta1 "k8s.io/client-go/listers/certificates/v1beta1"
 	"k8s.io/client-go/tools/cache"
 	"k8s.io/klog/v2"
@@ -261,3 +265,113 @@ func (m *NoopManager) GetTrustAnchorsByName(name string, allowMissing bool) ([]b
 func (m *NoopManager) GetTrustAnchorsBySigner(signerName string, labelSelector *metav1.LabelSelector, allowMissing bool) ([]byte, error) {
 	return nil, fmt.Errorf("ClusterTrustBundle projection is not supported in static kubelet mode")
 }
+
+// LazyInformerManager decides whether to use the noop or the actual manager on a call to
+// the manager's methods.
+// We cannot determine this upon startup because some may rely on the kubelet to be fully
+// running in order to setup their kube-apiserver.
+type LazyInformerManager struct {
+	manager           Manager
+	managerLock       sync.RWMutex
+	client            clientset.Interface
+	cacheSize         int
+	contextWithLogger context.Context
+	logger            logr.Logger
+}
+
+func NewLazyInformerManager(ctx context.Context, kubeClient clientset.Interface, cacheSize int) Manager {
+	return &LazyInformerManager{
+		client:            kubeClient,
+		cacheSize:         cacheSize,
+		contextWithLogger: ctx,
+		logger:            klog.FromContext(ctx),
+		managerLock:       sync.RWMutex{},
+	}
+}
+
+func (m *LazyInformerManager) GetTrustAnchorsByName(name string, allowMissing bool) ([]byte, error) {
+	if err := m.ensureManagerSet(); err != nil {
+		return nil, fmt.Errorf("failed to ensure informer manager for ClusterTrustBundles: %w", err)
+	}
+	return m.manager.GetTrustAnchorsByName(name, allowMissing)
+}
+
+func (m *LazyInformerManager) GetTrustAnchorsBySigner(signerName string, labelSelector *metav1.LabelSelector, allowMissing bool) ([]byte, error) {
+	if err := m.ensureManagerSet(); err != nil {
+		return nil, fmt.Errorf("failed to ensure informer manager for ClusterTrustBundles: %w", err)
+	}
+	return m.manager.GetTrustAnchorsBySigner(signerName, labelSelector, allowMissing)
+}
+
+func (m *LazyInformerManager) isManagerSet() bool {
+	m.managerLock.RLock()
+	defer m.managerLock.RUnlock()
+	return m.manager != nil
+}
+
+func (m *LazyInformerManager) ensureManagerSet() error {
+	if m.isManagerSet() {
+		return nil
+	}
+
+	m.managerLock.Lock()
+	defer m.managerLock.Unlock()
+	// we need to check again in case the manager was set between locking
+	if m.manager != nil {
+		return nil
+	}
+
+	ctbAPIAvailable, err := clusterTrustBundlesAvailable(m.client)
+	if err != nil {
+		return fmt.Errorf("failed to determine which informer manager to choose: %w", err)
+	}
+
+	if !ctbAPIAvailable {
+		m.manager = &NoopManager{}
+		return nil
+	}
+
+	kubeInformers := informers.NewSharedInformerFactoryWithOptions(m.client, 0)
+	clusterTrustBundleManager, err := NewInformerManager(m.contextWithLogger, kubeInformers.Certificates().V1beta1().ClusterTrustBundles(), m.cacheSize, 5*time.Minute)
+	if err != nil {
+		return fmt.Errorf("error starting informer-based ClusterTrustBundle manager: %w", err)
+	}
+	m.manager = clusterTrustBundleManager
+	kubeInformers.Start(m.contextWithLogger.Done())
+	m.logger.Info("Started ClusterTrustBundle informer")
+
+	// a cache fetch will likely follow right after, wait for the freshly started
+	// informers to sync
+	synced := true
+	timeoutContext, cancel := context.WithTimeout(m.contextWithLogger, 10*time.Second)
+	defer cancel()
+	m.logger.Info("Waiting for ClusterTrustBundle informer to sync")
+	for _, ok := range kubeInformers.WaitForCacheSync(timeoutContext.Done()) {
+		synced = synced && ok
+	}
+	if synced {
+		m.logger.Info("ClusterTrustBundle informer synced")
+	} else {
+		m.logger.Info("ClusterTrustBundle informer not synced, continuing to attempt in background")
+	}
+
+	return nil
+}
+
+func clusterTrustBundlesAvailable(client clientset.Interface) (bool, error) {
+	resList, err := client.Discovery().ServerResourcesForGroupVersion(certificatesv1beta1.SchemeGroupVersion.String())
+	if k8serrors.IsNotFound(err) {
+		return false, nil
+	}
+
+	if resList != nil {
+		// even in case of an error above there might be a partial list for APIs that
+		// were already successfully discovered
+		for _, r := range resList.APIResources {
+			if r.Name == "clustertrustbundles" {
+				return true, nil
+			}
+		}
+	}
+	return false, err
+}

pkg/kubelet/kubelet.go

@@ -878,19 +878,12 @@ func NewMainKubelet(kubeCfg *kubeletconfiginternal.KubeletConfiguration,
 
 	tokenManager := token.NewManager(kubeDeps.KubeClient)
 
-	var clusterTrustBundleManager clustertrustbundle.Manager
+	var clusterTrustBundleManager clustertrustbundle.Manager = &clustertrustbundle.NoopManager{}
 	if kubeDeps.KubeClient != nil && utilfeature.DefaultFeatureGate.Enabled(features.ClusterTrustBundleProjection) {
-		kubeInformers := informers.NewSharedInformerFactoryWithOptions(kubeDeps.KubeClient, 0)
-		clusterTrustBundleManager, err = clustertrustbundle.NewInformerManager(ctx, kubeInformers.Certificates().V1beta1().ClusterTrustBundles(), 2*int(kubeCfg.MaxPods), 5*time.Minute)
-		if err != nil {
-			return nil, fmt.Errorf("while starting informer-based ClusterTrustBundle manager: %w", err)
-		}
-		kubeInformers.Start(wait.NeverStop)
-		klog.InfoS("Started ClusterTrustBundle informer")
+		clusterTrustBundleManager = clustertrustbundle.NewLazyInformerManager(ctx, kubeDeps.KubeClient, 2*int(kubeCfg.MaxPods))
+		klog.InfoS("ClusterTrustBundle informer will be started eventually once a trust bundle is requested")
 	} else {
-		// In static kubelet mode, use a no-op manager.
-		clusterTrustBundleManager = &clustertrustbundle.NoopManager{}
-		klog.InfoS("Not starting ClusterTrustBundle informer because we are in static kubelet mode")
+		klog.InfoS("Not starting ClusterTrustBundle informer because we are in static kubelet mode or the ClusterTrustBundleProjection featuregate is disabled")
 	}
 
 	// NewInitializedVolumePluginMgr initializes some storageErrors on the Kubelet runtimeState (in csi_plugin.go init)