kubelet.go

/*
Copyright 2015 The Kubernetes Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package kubelet

import (
	"context"
	"crypto/tls"
	"fmt"
	"math"
	"net"
	"net/http"
	"os"
	"path"
	"path/filepath"
	sysruntime "runtime"
	"sort"
	"sync"
	"sync/atomic"
	"time"

	"github.com/opencontainers/selinux/go-selinux"
	"k8s.io/client-go/informers"

	cadvisorapi "github.com/google/cadvisor/info/v1"
	libcontaineruserns "github.com/opencontainers/runc/libcontainer/userns"
	"go.opentelemetry.io/otel/trace"
	"k8s.io/mount-utils"
	"k8s.io/utils/integer"
	netutils "k8s.io/utils/net"

	v1 "k8s.io/api/core/v1"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/fields"
	"k8s.io/apimachinery/pkg/labels"
	"k8s.io/apimachinery/pkg/types"
	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
	"k8s.io/apimachinery/pkg/util/sets"
	"k8s.io/apimachinery/pkg/util/wait"
	utilfeature "k8s.io/apiserver/pkg/util/feature"
	clientset "k8s.io/client-go/kubernetes"
	v1core "k8s.io/client-go/kubernetes/typed/core/v1"
	corelisters "k8s.io/client-go/listers/core/v1"
	"k8s.io/client-go/tools/cache"
	"k8s.io/client-go/tools/record"
	"k8s.io/client-go/util/certificate"
	"k8s.io/client-go/util/flowcontrol"
	cloudprovider "k8s.io/cloud-provider"
	"k8s.io/component-helpers/apimachinery/lease"
	internalapi "k8s.io/cri-api/pkg/apis"
	runtimeapi "k8s.io/cri-api/pkg/apis/runtime/v1"
	"k8s.io/klog/v2"
	pluginwatcherapi "k8s.io/kubelet/pkg/apis/pluginregistration/v1"
	statsapi "k8s.io/kubelet/pkg/apis/stats/v1alpha1"
	"k8s.io/kubernetes/pkg/features"
	kubeletconfiginternal "k8s.io/kubernetes/pkg/kubelet/apis/config"
	"k8s.io/kubernetes/pkg/kubelet/apis/podresources"
	"k8s.io/kubernetes/pkg/kubelet/cadvisor"
	kubeletcertificate "k8s.io/kubernetes/pkg/kubelet/certificate"
	"k8s.io/kubernetes/pkg/kubelet/cloudresource"
	"k8s.io/kubernetes/pkg/kubelet/cm"
	draplugin "k8s.io/kubernetes/pkg/kubelet/cm/dra/plugin"
	"k8s.io/kubernetes/pkg/kubelet/config"
	"k8s.io/kubernetes/pkg/kubelet/configmap"
	kubecontainer "k8s.io/kubernetes/pkg/kubelet/container"
	"k8s.io/kubernetes/pkg/kubelet/cri/remote"
	"k8s.io/kubernetes/pkg/kubelet/events"
	"k8s.io/kubernetes/pkg/kubelet/eviction"
	"k8s.io/kubernetes/pkg/kubelet/images"
	"k8s.io/kubernetes/pkg/kubelet/kuberuntime"
	"k8s.io/kubernetes/pkg/kubelet/lifecycle"
	"k8s.io/kubernetes/pkg/kubelet/logs"
	"k8s.io/kubernetes/pkg/kubelet/metrics"
	"k8s.io/kubernetes/pkg/kubelet/metrics/collectors"
	"k8s.io/kubernetes/pkg/kubelet/network/dns"
	"k8s.io/kubernetes/pkg/kubelet/nodeshutdown"
	oomwatcher "k8s.io/kubernetes/pkg/kubelet/oom"
	"k8s.io/kubernetes/pkg/kubelet/pleg"
	"k8s.io/kubernetes/pkg/kubelet/pluginmanager"
	plugincache "k8s.io/kubernetes/pkg/kubelet/pluginmanager/cache"
	kubepod "k8s.io/kubernetes/pkg/kubelet/pod"
	"k8s.io/kubernetes/pkg/kubelet/preemption"
	"k8s.io/kubernetes/pkg/kubelet/prober"
	proberesults "k8s.io/kubernetes/pkg/kubelet/prober/results"
	"k8s.io/kubernetes/pkg/kubelet/runtimeclass"
	"k8s.io/kubernetes/pkg/kubelet/secret"
	"k8s.io/kubernetes/pkg/kubelet/server"
	servermetrics "k8s.io/kubernetes/pkg/kubelet/server/metrics"
	serverstats "k8s.io/kubernetes/pkg/kubelet/server/stats"
	"k8s.io/kubernetes/pkg/kubelet/stats"
	"k8s.io/kubernetes/pkg/kubelet/status"
	"k8s.io/kubernetes/pkg/kubelet/sysctl"
	"k8s.io/kubernetes/pkg/kubelet/token"
	kubetypes "k8s.io/kubernetes/pkg/kubelet/types"
	"k8s.io/kubernetes/pkg/kubelet/util"
	"k8s.io/kubernetes/pkg/kubelet/util/manager"
	"k8s.io/kubernetes/pkg/kubelet/util/queue"
	"k8s.io/kubernetes/pkg/kubelet/util/sliceutils"
	"k8s.io/kubernetes/pkg/kubelet/volumemanager"
	httpprobe "k8s.io/kubernetes/pkg/probe/http"
	"k8s.io/kubernetes/pkg/security/apparmor"
	"k8s.io/kubernetes/pkg/util/oom"
	"k8s.io/kubernetes/pkg/volume"
	"k8s.io/kubernetes/pkg/volume/csi"
	"k8s.io/kubernetes/pkg/volume/util/hostutil"
	"k8s.io/kubernetes/pkg/volume/util/subpath"
	"k8s.io/kubernetes/pkg/volume/util/volumepathhandler"
	"k8s.io/utils/clock"
)

const (
	// Max amount of time to wait for the container runtime to come up.
	maxWaitForContainerRuntime = 30 * time.Second

	// nodeStatusUpdateRetry specifies how many times kubelet retries when posting node status failed.
	nodeStatusUpdateRetry = 5

	// nodeReadyGracePeriod is the period to allow for before fast status update is
	// terminated and container runtime not being ready is logged without verbosity guard.
	nodeReadyGracePeriod = 120 * time.Second

	// DefaultContainerLogsDir is the location of container logs.
	DefaultContainerLogsDir = "/var/log/containers"

	// MaxContainerBackOff is the max backoff period, exported for the e2e test
	MaxContainerBackOff = 300 * time.Second

	// Period for performing global cleanup tasks.
	housekeepingPeriod = time.Second * 2

	// Duration at which housekeeping failed to satisfy the invariant that
	// housekeeping should be fast to avoid blocking pod config (while
	// housekeeping is running no new pods are started or deleted).
	housekeepingWarningDuration = time.Second * 15

	// Period for performing eviction monitoring.
	// ensure this is kept in sync with internal cadvisor housekeeping.
	evictionMonitoringPeriod = time.Second * 10

	// The path in containers' filesystems where the hosts file is mounted.
	linuxEtcHostsPath   = "/etc/hosts"
	windowsEtcHostsPath = "C:\\Windows\\System32\\drivers\\etc\\hosts"

	// Capacity of the channel for receiving pod lifecycle events. This number
	// is a bit arbitrary and may be adjusted in the future.
	plegChannelCapacity = 1000

	// Generic PLEG relies on relisting for discovering container events.
	// A longer period means that kubelet will take longer to detect container
	// changes and to update pod status. On the other hand, a shorter period
	// will cause more frequent relisting (e.g., container runtime operations),
	// leading to higher cpu usage.
	// Note that even though we set the period to 1s, the relisting itself can
	// take more than 1s to finish if the container runtime responds slowly
	// and/or when there are many container changes in one cycle.
	genericPlegRelistPeriod    = time.Second * 1
	genericPlegRelistThreshold = time.Minute * 3

	// Generic PLEG relist period and threshold when used with Evented PLEG.
	eventedPlegRelistPeriod     = time.Second * 300
	eventedPlegRelistThreshold  = time.Minute * 10
	eventedPlegMaxStreamRetries = 5

	// backOffPeriod is the period to back off when pod syncing results in an
	// error. It is also used as the base period for the exponential backoff
	// container restarts and image pulls.
	backOffPeriod = time.Second * 10

	// ContainerGCPeriod is the period for performing container garbage collection.
	ContainerGCPeriod = time.Minute
	// ImageGCPeriod is the period for performing image garbage collection.
	ImageGCPeriod = 5 * time.Minute

	// Minimum number of dead containers to keep in a pod
	minDeadContainerInPod = 1

	// nodeLeaseRenewIntervalFraction is the fraction of lease duration to renew the lease
	nodeLeaseRenewIntervalFraction = 0.25
)

var (
	// ContainerLogsDir can be overwrited for testing usage
	ContainerLogsDir = DefaultContainerLogsDir
	etcHostsPath     = getContainerEtcHostsPath()
)

func getContainerEtcHostsPath() string {
	if sysruntime.GOOS == "windows" {
		return windowsEtcHostsPath
	}
	return linuxEtcHostsPath
}

// SyncHandler is an interface implemented by Kubelet, for testability
type SyncHandler interface {
	HandlePodAdditions(pods []*v1.Pod)
	HandlePodUpdates(pods []*v1.Pod)
	HandlePodRemoves(pods []*v1.Pod)
	HandlePodReconcile(pods []*v1.Pod)
	HandlePodSyncs(pods []*v1.Pod)
	HandlePodCleanups(ctx context.Context) error
}

// Option is a functional option type for Kubelet
type Option func(*Kubelet)

// Bootstrap is a bootstrapping interface for kubelet, targets the initialization protocol
type Bootstrap interface {
	GetConfiguration() kubeletconfiginternal.KubeletConfiguration
	BirthCry()
	StartGarbageCollection()
	ListenAndServe(kubeCfg *kubeletconfiginternal.KubeletConfiguration, tlsOptions *server.TLSOptions, auth server.AuthInterface, tp trace.TracerProvider)
	ListenAndServeReadOnly(address net.IP, port uint)
	ListenAndServePodResources()
	Run(<-chan kubetypes.PodUpdate)
	RunOnce(<-chan kubetypes.PodUpdate) ([]RunPodResult, error)
}

// Dependencies is a bin for things we might consider "injected dependencies" -- objects constructed
// at runtime that are necessary for running the Kubelet. This is a temporary solution for grouping
// these objects while we figure out a more comprehensive dependency injection story for the Kubelet.
type Dependencies struct {
	Options []Option

	// Injected Dependencies
	Auth                     server.AuthInterface
	CAdvisorInterface        cadvisor.Interface
	Cloud                    cloudprovider.Interface
	ContainerManager         cm.ContainerManager
	EventClient              v1core.EventsGetter
	HeartbeatClient          clientset.Interface
	OnHeartbeatFailure       func()
	KubeClient               clientset.Interface
	Mounter                  mount.Interface
	HostUtil                 hostutil.HostUtils
	OOMAdjuster              *oom.OOMAdjuster
	OSInterface              kubecontainer.OSInterface
	PodConfig                *config.PodConfig
	ProbeManager             prober.Manager
	Recorder                 record.EventRecorder
	Subpather                subpath.Interface
	TracerProvider           trace.TracerProvider
	VolumePlugins            []volume.VolumePlugin
	DynamicPluginProber      volume.DynamicPluginProber
	TLSOptions               *server.TLSOptions
	RemoteRuntimeService     internalapi.RuntimeService
	RemoteImageService       internalapi.ImageManagerService
	PodStartupLatencyTracker util.PodStartupLatencyTracker
	// remove it after cadvisor.UsingLegacyCadvisorStats dropped.
	useLegacyCadvisorStats bool
}

// makePodSourceConfig creates a config.PodConfig from the given
// KubeletConfiguration or returns an error.
func makePodSourceConfig(kubeCfg *kubeletconfiginternal.KubeletConfiguration, kubeDeps *Dependencies, nodeName types.NodeName, nodeHasSynced func() bool) (*config.PodConfig, error) {
	manifestURLHeader := make(http.Header)
	if len(kubeCfg.StaticPodURLHeader) > 0 {
		for k, v := range kubeCfg.StaticPodURLHeader {
			for i := range v {
				manifestURLHeader.Add(k, v[i])
			}
		}
	}

	// source of all configuration
	cfg := config.NewPodConfig(config.PodConfigNotificationIncremental, kubeDeps.Recorder, kubeDeps.PodStartupLatencyTracker)

	// TODO:  it needs to be replaced by a proper context in the future
	ctx := context.TODO()

	// define file config source
	if kubeCfg.StaticPodPath != "" {
		klog.InfoS("Adding static pod path", "path", kubeCfg.StaticPodPath)
		config.NewSourceFile(kubeCfg.StaticPodPath, nodeName, kubeCfg.FileCheckFrequency.Duration, cfg.Channel(ctx, kubetypes.FileSource))
	}

	// define url config source
	if kubeCfg.StaticPodURL != "" {
		klog.InfoS("Adding pod URL with HTTP header", "URL", kubeCfg.StaticPodURL, "header", manifestURLHeader)
		config.NewSourceURL(kubeCfg.StaticPodURL, manifestURLHeader, nodeName, kubeCfg.HTTPCheckFrequency.Duration, cfg.Channel(ctx, kubetypes.HTTPSource))
	}

	if kubeDeps.KubeClient != nil {
		klog.InfoS("Adding apiserver pod source")
		config.NewSourceApiserver(kubeDeps.KubeClient, nodeName, nodeHasSynced, cfg.Channel(ctx, kubetypes.ApiserverSource))
	}
	return cfg, nil
}

// PreInitRuntimeService will init runtime service before RunKubelet.
func PreInitRuntimeService(kubeCfg *kubeletconfiginternal.KubeletConfiguration,
	kubeDeps *Dependencies,
	remoteRuntimeEndpoint string,
	remoteImageEndpoint string) error {
	// remoteImageEndpoint is same as remoteRuntimeEndpoint if not explicitly specified
	if remoteRuntimeEndpoint != "" && remoteImageEndpoint == "" {
		remoteImageEndpoint = remoteRuntimeEndpoint
	}

	var err error
	if kubeDeps.RemoteRuntimeService, err = remote.NewRemoteRuntimeService(remoteRuntimeEndpoint, kubeCfg.RuntimeRequestTimeout.Duration, kubeDeps.TracerProvider); err != nil {
		return err
	}
	if kubeDeps.RemoteImageService, err = remote.NewRemoteImageService(remoteImageEndpoint, kubeCfg.RuntimeRequestTimeout.Duration, kubeDeps.TracerProvider); err != nil {
		return err
	}

	kubeDeps.useLegacyCadvisorStats = cadvisor.UsingLegacyCadvisorStats(remoteRuntimeEndpoint)

	return nil
}

// NewMainKubelet instantiates a new Kubelet object along with all the required internal modules.
// No initialization of Kubelet and its modules should happen here.
func NewMainKubelet(kubeCfg *kubeletconfiginternal.KubeletConfiguration,
	kubeDeps *Dependencies,
	crOptions *config.ContainerRuntimeOptions,
	hostname string,
	hostnameOverridden bool,
	nodeName types.NodeName,
	nodeIPs []net.IP,
	providerID string,
	cloudProvider string,
	certDirectory string,
	rootDirectory string,
	imageCredentialProviderConfigFile string,
	imageCredentialProviderBinDir string,
	registerNode bool,
	registerWithTaints []v1.Taint,
	allowedUnsafeSysctls []string,
	experimentalMounterPath string,
	kernelMemcgNotification bool,
	experimentalNodeAllocatableIgnoreEvictionThreshold bool,
	minimumGCAge metav1.Duration,
	maxPerPodContainerCount int32,
	maxContainerCount int32,
	masterServiceNamespace string,
	registerSchedulable bool,
	keepTerminatedPodVolumes bool,
	nodeLabels map[string]string,
	nodeStatusMaxImages int32,
	seccompDefault bool,
) (*Kubelet, error) {
	ctx := context.Background()
	logger := klog.TODO()

	if rootDirectory == "" {
		return nil, fmt.Errorf("invalid root directory %q", rootDirectory)
	}
	if kubeCfg.SyncFrequency.Duration <= 0 {
		return nil, fmt.Errorf("invalid sync frequency %d", kubeCfg.SyncFrequency.Duration)
	}

	if kubeCfg.MakeIPTablesUtilChains {
		if kubeCfg.IPTablesMasqueradeBit > 31 || kubeCfg.IPTablesMasqueradeBit < 0 {
			return nil, fmt.Errorf("iptables-masquerade-bit is not valid. Must be within [0, 31]")
		}
		if kubeCfg.IPTablesDropBit > 31 || kubeCfg.IPTablesDropBit < 0 {
			return nil, fmt.Errorf("iptables-drop-bit is not valid. Must be within [0, 31]")
		}
		if kubeCfg.IPTablesDropBit == kubeCfg.IPTablesMasqueradeBit {
			return nil, fmt.Errorf("iptables-masquerade-bit and iptables-drop-bit must be different")
		}
	}

	if utilfeature.DefaultFeatureGate.Enabled(features.DisableCloudProviders) && cloudprovider.IsDeprecatedInternal(cloudProvider) {
		cloudprovider.DisableWarningForProvider(cloudProvider)
		return nil, fmt.Errorf("cloud provider %q was specified, but built-in cloud providers are disabled. Please set --cloud-provider=external and migrate to an external cloud provider", cloudProvider)
	}

	var nodeHasSynced cache.InformerSynced
	var nodeLister corelisters.NodeLister

	// If kubeClient == nil, we are running in standalone mode (i.e. no API servers)
	// If not nil, we are running as part of a cluster and should sync w/API
	if kubeDeps.KubeClient != nil {
		kubeInformers := informers.NewSharedInformerFactoryWithOptions(kubeDeps.KubeClient, 0, informers.WithTweakListOptions(func(options *metav1.ListOptions) {
			options.FieldSelector = fields.Set{metav1.ObjectNameField: string(nodeName)}.String()
		}))
		nodeLister = kubeInformers.Core().V1().Nodes().Lister()
		nodeHasSynced = func() bool {
			return kubeInformers.Core().V1().Nodes().Informer().HasSynced()
		}
		kubeInformers.Start(wait.NeverStop)
		klog.InfoS("Attempting to sync node with API server")
	} else {
		// we don't have a client to sync!
		nodeIndexer := cache.NewIndexer(cache.MetaNamespaceKeyFunc, cache.Indexers{})
		nodeLister = corelisters.NewNodeLister(nodeIndexer)
		nodeHasSynced = func() bool { return true }
		klog.InfoS("Kubelet is running in standalone mode, will skip API server sync")
	}

	if kubeDeps.PodConfig == nil {
		var err error
		kubeDeps.PodConfig, err = makePodSourceConfig(kubeCfg, kubeDeps, nodeName, nodeHasSynced)
		if err != nil {
			return nil, err
		}
	}

	containerGCPolicy := kubecontainer.GCPolicy{
		MinAge:             minimumGCAge.Duration,
		MaxPerPodContainer: int(maxPerPodContainerCount),
		MaxContainers:      int(maxContainerCount),
	}

	daemonEndpoints := &v1.NodeDaemonEndpoints{
		KubeletEndpoint: v1.DaemonEndpoint{Port: kubeCfg.Port},
	}

	imageGCPolicy := images.ImageGCPolicy{
		MinAge:               kubeCfg.ImageMinimumGCAge.Duration,
		HighThresholdPercent: int(kubeCfg.ImageGCHighThresholdPercent),
		LowThresholdPercent:  int(kubeCfg.ImageGCLowThresholdPercent),
	}

	enforceNodeAllocatable := kubeCfg.EnforceNodeAllocatable
	if experimentalNodeAllocatableIgnoreEvictionThreshold {
		// Do not provide kubeCfg.EnforceNodeAllocatable to eviction threshold parsing if we are not enforcing Evictions
		enforceNodeAllocatable = []string{}
	}
	thresholds, err := eviction.ParseThresholdConfig(enforceNodeAllocatable, kubeCfg.EvictionHard, kubeCfg.EvictionSoft, kubeCfg.EvictionSoftGracePeriod, kubeCfg.EvictionMinimumReclaim)
	if err != nil {
		return nil, err
	}
	evictionConfig := eviction.Config{
		PressureTransitionPeriod: kubeCfg.EvictionPressureTransitionPeriod.Duration,
		MaxPodGracePeriodSeconds: int64(kubeCfg.EvictionMaxPodGracePeriod),
		Thresholds:               thresholds,
		KernelMemcgNotification:  kernelMemcgNotification,
		PodCgroupRoot:            kubeDeps.ContainerManager.GetPodCgroupRoot(),
	}

	var serviceLister corelisters.ServiceLister
	var serviceHasSynced cache.InformerSynced
	if kubeDeps.KubeClient != nil {
		kubeInformers := informers.NewSharedInformerFactory(kubeDeps.KubeClient, 0)
		serviceLister = kubeInformers.Core().V1().Services().Lister()
		serviceHasSynced = kubeInformers.Core().V1().Services().Informer().HasSynced
		kubeInformers.Start(wait.NeverStop)
	} else {
		serviceIndexer := cache.NewIndexer(cache.MetaNamespaceKeyFunc, cache.Indexers{cache.NamespaceIndex: cache.MetaNamespaceIndexFunc})
		serviceLister = corelisters.NewServiceLister(serviceIndexer)
		serviceHasSynced = func() bool { return true }
	}

	// construct a node reference used for events
	nodeRef := &v1.ObjectReference{
		Kind:      "Node",
		Name:      string(nodeName),
		UID:       types.UID(nodeName),
		Namespace: "",
	}

	oomWatcher, err := oomwatcher.NewWatcher(kubeDeps.Recorder)
	if err != nil {
		if libcontaineruserns.RunningInUserNS() {
			if utilfeature.DefaultFeatureGate.Enabled(features.KubeletInUserNamespace) {
				// oomwatcher.NewWatcher returns "open /dev/kmsg: operation not permitted" error,
				// when running in a user namespace with sysctl value `kernel.dmesg_restrict=1`.
				klog.V(2).InfoS("Failed to create an oomWatcher (running in UserNS, ignoring)", "err", err)
				oomWatcher = nil
			} else {
				klog.ErrorS(err, "Failed to create an oomWatcher (running in UserNS, Hint: enable KubeletInUserNamespace feature flag to ignore the error)")
				return nil, err
			}
		} else {
			return nil, err
		}
	}

	clusterDNS := make([]net.IP, 0, len(kubeCfg.ClusterDNS))
	for _, ipEntry := range kubeCfg.ClusterDNS {
		ip := netutils.ParseIPSloppy(ipEntry)
		if ip == nil {
			klog.InfoS("Invalid clusterDNS IP", "IP", ipEntry)
		} else {
			clusterDNS = append(clusterDNS, ip)
		}
	}

	// A TLS transport is needed to make HTTPS-based container lifecycle requests,
	// but we do not have the information necessary to do TLS verification.
	//
	// This client must not be modified to include credentials, because it is
	// critical that credentials not leak from the client to arbitrary hosts.
	insecureContainerLifecycleHTTPClient := &http.Client{}
	if utilfeature.DefaultFeatureGate.Enabled(features.ConsistentHTTPGetHandlers) {
		insecureTLSTransport := &http.Transport{
			TLSClientConfig: &tls.Config{InsecureSkipVerify: true},
		}
		insecureContainerLifecycleHTTPClient.Transport = insecureTLSTransport
		insecureContainerLifecycleHTTPClient.CheckRedirect = httpprobe.RedirectChecker(false)
	}

	klet := &Kubelet{
		hostname:                                hostname,
		hostnameOverridden:                      hostnameOverridden,
		nodeName:                                nodeName,
		kubeClient:                              kubeDeps.KubeClient,
		heartbeatClient:                         kubeDeps.HeartbeatClient,
		onRepeatedHeartbeatFailure:              kubeDeps.OnHeartbeatFailure,
		rootDirectory:                           rootDirectory,
		resyncInterval:                          kubeCfg.SyncFrequency.Duration,
		sourcesReady:                            config.NewSourcesReady(kubeDeps.PodConfig.SeenAllSources),
		registerNode:                            registerNode,
		registerWithTaints:                      registerWithTaints,
		registerSchedulable:                     registerSchedulable,
		dnsConfigurer:                           dns.NewConfigurer(kubeDeps.Recorder, nodeRef, nodeIPs, clusterDNS, kubeCfg.ClusterDomain, kubeCfg.ResolverConfig),
		serviceLister:                           serviceLister,
		serviceHasSynced:                        serviceHasSynced,
		nodeLister:                              nodeLister,
		nodeHasSynced:                           nodeHasSynced,
		masterServiceNamespace:                  masterServiceNamespace,
		streamingConnectionIdleTimeout:          kubeCfg.StreamingConnectionIdleTimeout.Duration,
		recorder:                                kubeDeps.Recorder,
		cadvisor:                                kubeDeps.CAdvisorInterface,
		cloud:                                   kubeDeps.Cloud,
		externalCloudProvider:                   cloudprovider.IsExternal(cloudProvider),
		providerID:                              providerID,
		nodeRef:                                 nodeRef,
		nodeLabels:                              nodeLabels,
		nodeStatusUpdateFrequency:               kubeCfg.NodeStatusUpdateFrequency.Duration,
		nodeStatusReportFrequency:               kubeCfg.NodeStatusReportFrequency.Duration,
		os:                                      kubeDeps.OSInterface,
		oomWatcher:                              oomWatcher,
		cgroupsPerQOS:                           kubeCfg.CgroupsPerQOS,
		cgroupRoot:                              kubeCfg.CgroupRoot,
		mounter:                                 kubeDeps.Mounter,
		hostutil:                                kubeDeps.HostUtil,
		subpather:                               kubeDeps.Subpather,
		maxPods:                                 int(kubeCfg.MaxPods),
		podsPerCore:                             int(kubeCfg.PodsPerCore),
		syncLoopMonitor:                         atomic.Value{},
		daemonEndpoints:                         daemonEndpoints,
		containerManager:                        kubeDeps.ContainerManager,
		nodeIPs:                                 nodeIPs,
		nodeIPValidator:                         validateNodeIP,
		clock:                                   clock.RealClock{},
		enableControllerAttachDetach:            kubeCfg.EnableControllerAttachDetach,
		makeIPTablesUtilChains:                  kubeCfg.MakeIPTablesUtilChains,
		iptablesMasqueradeBit:                   int(kubeCfg.IPTablesMasqueradeBit),
		iptablesDropBit:                         int(kubeCfg.IPTablesDropBit),
		experimentalHostUserNamespaceDefaulting: utilfeature.DefaultFeatureGate.Enabled(features.ExperimentalHostUserNamespaceDefaultingGate),
		keepTerminatedPodVolumes:                keepTerminatedPodVolumes,
		nodeStatusMaxImages:                     nodeStatusMaxImages,
	}

	if klet.cloud != nil {
		klet.cloudResourceSyncManager = cloudresource.NewSyncManager(klet.cloud, nodeName, klet.nodeStatusUpdateFrequency)
	}

	var secretManager secret.Manager
	var configMapManager configmap.Manager
	if klet.kubeClient != nil {
		switch kubeCfg.ConfigMapAndSecretChangeDetectionStrategy {
		case kubeletconfiginternal.WatchChangeDetectionStrategy:
			secretManager = secret.NewWatchingSecretManager(klet.kubeClient, klet.resyncInterval)
			configMapManager = configmap.NewWatchingConfigMapManager(klet.kubeClient, klet.resyncInterval)
		case kubeletconfiginternal.TTLCacheChangeDetectionStrategy:
			secretManager = secret.NewCachingSecretManager(
				klet.kubeClient, manager.GetObjectTTLFromNodeFunc(klet.GetNode))
			configMapManager = configmap.NewCachingConfigMapManager(
				klet.kubeClient, manager.GetObjectTTLFromNodeFunc(klet.GetNode))
		case kubeletconfiginternal.GetChangeDetectionStrategy:
			secretManager = secret.NewSimpleSecretManager(klet.kubeClient)
			configMapManager = configmap.NewSimpleConfigMapManager(klet.kubeClient)
		default:
			return nil, fmt.Errorf("unknown configmap and secret manager mode: %v", kubeCfg.ConfigMapAndSecretChangeDetectionStrategy)
		}

		klet.secretManager = secretManager
		klet.configMapManager = configMapManager
	}

	if klet.experimentalHostUserNamespaceDefaulting {
		klog.InfoS("Experimental host user namespace defaulting is enabled")
	}

	machineInfo, err := klet.cadvisor.MachineInfo()
	if err != nil {
		return nil, err
	}
	// Avoid collector collects it as a timestamped metric
	// See PR #95210 and #97006 for more details.
	machineInfo.Timestamp = time.Time{}
	klet.setCachedMachineInfo(machineInfo)

	imageBackOff := flowcontrol.NewBackOff(backOffPeriod, MaxContainerBackOff)

	klet.livenessManager = proberesults.NewManager()
	klet.readinessManager = proberesults.NewManager()
	klet.startupManager = proberesults.NewManager()
	klet.podCache = kubecontainer.NewCache()

	// podManager is also responsible for keeping secretManager and configMapManager contents up-to-date.
	mirrorPodClient := kubepod.NewBasicMirrorClient(klet.kubeClient, string(nodeName), nodeLister)
	klet.podManager = kubepod.NewBasicPodManager(mirrorPodClient, secretManager, configMapManager)

	klet.statusManager = status.NewManager(klet.kubeClient, klet.podManager, klet, kubeDeps.PodStartupLatencyTracker)

	klet.resourceAnalyzer = serverstats.NewResourceAnalyzer(klet, kubeCfg.VolumeStatsAggPeriod.Duration, kubeDeps.Recorder)

	klet.runtimeService = kubeDeps.RemoteRuntimeService

	if kubeDeps.KubeClient != nil {
		klet.runtimeClassManager = runtimeclass.NewManager(kubeDeps.KubeClient)
	}

	// setup containerLogManager for CRI container runtime
	containerLogManager, err := logs.NewContainerLogManager(
		klet.runtimeService,
		kubeDeps.OSInterface,
		kubeCfg.ContainerLogMaxSize,
		int(kubeCfg.ContainerLogMaxFiles),
	)
	if err != nil {
		return nil, fmt.Errorf("failed to initialize container log manager: %v", err)
	}
	klet.containerLogManager = containerLogManager

	klet.reasonCache = NewReasonCache()
	klet.workQueue = queue.NewBasicWorkQueue(klet.clock)
	klet.podWorkers = newPodWorkers(
		klet.syncPod,
		klet.syncTerminatingPod,
		klet.syncTerminatedPod,

		kubeDeps.Recorder,
		klet.workQueue,
		klet.resyncInterval,
		backOffPeriod,
		klet.podCache,
	)

	runtime, err := kuberuntime.NewKubeGenericRuntimeManager(
		kubecontainer.FilterEventRecorder(kubeDeps.Recorder),
		klet.livenessManager,
		klet.readinessManager,
		klet.startupManager,
		rootDirectory,
		machineInfo,
		klet.podWorkers,
		kubeDeps.OSInterface,
		klet,
		insecureContainerLifecycleHTTPClient,
		imageBackOff,
		kubeCfg.SerializeImagePulls,
		float32(kubeCfg.RegistryPullQPS),
		int(kubeCfg.RegistryBurst),
		imageCredentialProviderConfigFile,
		imageCredentialProviderBinDir,
		kubeCfg.CPUCFSQuota,
		kubeCfg.CPUCFSQuotaPeriod,
		kubeDeps.RemoteRuntimeService,
		kubeDeps.RemoteImageService,
		kubeDeps.ContainerManager.InternalContainerLifecycle(),
		klet.containerLogManager,
		klet.runtimeClassManager,
		seccompDefault,
		kubeCfg.MemorySwap.SwapBehavior,
		kubeDeps.ContainerManager.GetNodeAllocatableAbsolute,
		*kubeCfg.MemoryThrottlingFactor,
		kubeDeps.PodStartupLatencyTracker,
	)
	if err != nil {
		return nil, err
	}
	klet.containerRuntime = runtime
	klet.streamingRuntime = runtime
	klet.runner = runtime

	runtimeCache, err := kubecontainer.NewRuntimeCache(klet.containerRuntime)
	if err != nil {
		return nil, err
	}
	klet.runtimeCache = runtimeCache

	// common provider to get host file system usage associated with a pod managed by kubelet
	hostStatsProvider := stats.NewHostStatsProvider(kubecontainer.RealOS{}, func(podUID types.UID) string {
		return getEtcHostsPath(klet.getPodDir(podUID))
	})
	if kubeDeps.useLegacyCadvisorStats {
		klet.StatsProvider = stats.NewCadvisorStatsProvider(
			klet.cadvisor,
			klet.resourceAnalyzer,
			klet.podManager,
			klet.runtimeCache,
			klet.containerRuntime,
			klet.statusManager,
			hostStatsProvider)
	} else {
		klet.StatsProvider = stats.NewCRIStatsProvider(
			klet.cadvisor,
			klet.resourceAnalyzer,
			klet.podManager,
			klet.runtimeCache,
			kubeDeps.RemoteRuntimeService,
			kubeDeps.RemoteImageService,
			hostStatsProvider,
			utilfeature.DefaultFeatureGate.Enabled(features.PodAndContainerStatsFromCRI))
	}

	eventChannel := make(chan *pleg.PodLifecycleEvent, plegChannelCapacity)

	if utilfeature.DefaultFeatureGate.Enabled(features.EventedPLEG) {
		// adjust Generic PLEG relisting period and threshold to higher value when Evented PLEG is turned on
		genericRelistDuration := &pleg.RelistDuration{
			RelistPeriod:    eventedPlegRelistPeriod,
			RelistThreshold: eventedPlegRelistThreshold,
		}
		klet.pleg = pleg.NewGenericPLEG(klet.containerRuntime, eventChannel, genericRelistDuration, klet.podCache, clock.RealClock{})
		// In case Evented PLEG has to fall back on Generic PLEG due to an error,
		// Evented PLEG should be able to reset the Generic PLEG relisting duration
		// to the default value.
		eventedRelistDuration := &pleg.RelistDuration{
			RelistPeriod:    genericPlegRelistPeriod,
			RelistThreshold: genericPlegRelistThreshold,
		}
		klet.eventedPleg = pleg.NewEventedPLEG(klet.containerRuntime, klet.runtimeService, eventChannel,
			klet.podCache, klet.pleg, eventedPlegMaxStreamRetries, eventedRelistDuration, clock.RealClock{})
	} else {
		genericRelistDuration := &pleg.RelistDuration{
			RelistPeriod:    genericPlegRelistPeriod,
			RelistThreshold: genericPlegRelistThreshold,
		}
		klet.pleg = pleg.NewGenericPLEG(klet.containerRuntime, eventChannel, genericRelistDuration, klet.podCache, clock.RealClock{})
	}

	klet.runtimeState = newRuntimeState(maxWaitForContainerRuntime)
	klet.runtimeState.addHealthCheck("PLEG", klet.pleg.Healthy)
	if utilfeature.DefaultFeatureGate.Enabled(features.EventedPLEG) {
		klet.runtimeState.addHealthCheck("EventedPLEG", klet.eventedPleg.Healthy)
	}
	if _, err := klet.updatePodCIDR(ctx, kubeCfg.PodCIDR); err != nil {
		klog.ErrorS(err, "Pod CIDR update failed")
	}

	// setup containerGC
	containerGC, err := kubecontainer.NewContainerGC(klet.containerRuntime, containerGCPolicy, klet.sourcesReady)
	if err != nil {
		return nil, err
	}
	klet.containerGC = containerGC
	klet.containerDeletor = newPodContainerDeletor(klet.containerRuntime, integer.IntMax(containerGCPolicy.MaxPerPodContainer, minDeadContainerInPod))

	// setup imageManager
	imageManager, err := images.NewImageGCManager(klet.containerRuntime, klet.StatsProvider, kubeDeps.Recorder, nodeRef, imageGCPolicy, crOptions.PodSandboxImage)
	if err != nil {
		return nil, fmt.Errorf("failed to initialize image manager: %v", err)
	}
	klet.imageManager = imageManager

	if kubeCfg.ServerTLSBootstrap && kubeDeps.TLSOptions != nil && utilfeature.DefaultFeatureGate.Enabled(features.RotateKubeletServerCertificate) {
		klet.serverCertificateManager, err = kubeletcertificate.NewKubeletServerCertificateManager(klet.kubeClient, kubeCfg, klet.nodeName, klet.getLastObservedNodeAddresses, certDirectory)
		if err != nil {
			return nil, fmt.Errorf("failed to initialize certificate manager: %v", err)
		}
		kubeDeps.TLSOptions.Config.GetCertificate = func(*tls.ClientHelloInfo) (*tls.Certificate, error) {
			cert := klet.serverCertificateManager.Current()
			if cert == nil {
				return nil, fmt.Errorf("no serving certificate available for the kubelet")
			}
			return cert, nil
		}
	}

	if kubeDeps.ProbeManager != nil {
		klet.probeManager = kubeDeps.ProbeManager
	} else {
		klet.probeManager = prober.NewManager(
			klet.statusManager,
			klet.livenessManager,
			klet.readinessManager,
			klet.startupManager,
			klet.runner,
			kubeDeps.Recorder)
	}

	tokenManager := token.NewManager(kubeDeps.KubeClient)

	// NewInitializedVolumePluginMgr initializes some storageErrors on the Kubelet runtimeState (in csi_plugin.go init)
	// which affects node ready status. This function must be called before Kubelet is initialized so that the Node
	// ReadyState is accurate with the storage state.
	klet.volumePluginMgr, err =
		NewInitializedVolumePluginMgr(klet, secretManager, configMapManager, tokenManager, kubeDeps.VolumePlugins, kubeDeps.DynamicPluginProber)
	if err != nil {
		return nil, err
	}
	klet.pluginManager = pluginmanager.NewPluginManager(
		klet.getPluginsRegistrationDir(), /* sockDir */
		kubeDeps.Recorder,
	)

	// If the experimentalMounterPathFlag is set, we do not want to
	// check node capabilities since the mount path is not the default
	if len(experimentalMounterPath) != 0 {
		// Replace the nameserver in containerized-mounter's rootfs/etc/resolv.conf with kubelet.ClusterDNS
		// so that service name could be resolved
		klet.dnsConfigurer.SetupDNSinContainerizedMounter(experimentalMounterPath)
	}

	// setup volumeManager
	klet.volumeManager = volumemanager.NewVolumeManager(
		kubeCfg.EnableControllerAttachDetach,
		nodeName,
		klet.podManager,
		klet.podWorkers,
		klet.kubeClient,
		klet.volumePluginMgr,
		klet.containerRuntime,
		kubeDeps.Mounter,
		kubeDeps.HostUtil,
		klet.getPodsDir(),
		kubeDeps.Recorder,
		keepTerminatedPodVolumes,
		volumepathhandler.NewBlockVolumePathHandler())

	klet.backOff = flowcontrol.NewBackOff(backOffPeriod, MaxContainerBackOff)

	// setup eviction manager
	evictionManager, evictionAdmitHandler := eviction.NewManager(klet.resourceAnalyzer, evictionConfig,
		killPodNow(klet.podWorkers, kubeDeps.Recorder), klet.podManager.GetMirrorPodByPod, klet.imageManager, klet.containerGC, kubeDeps.Recorder, nodeRef, klet.clock, kubeCfg.LocalStorageCapacityIsolation)

	klet.evictionManager = evictionManager
	klet.admitHandlers.AddPodAdmitHandler(evictionAdmitHandler)

	// Safe, allowed sysctls can always be used as unsafe sysctls in the spec.
	// Hence, we concatenate those two lists.
	safeAndUnsafeSysctls := append(sysctl.SafeSysctlAllowlist(), allowedUnsafeSysctls...)
	sysctlsAllowlist, err := sysctl.NewAllowlist(safeAndUnsafeSysctls)
	if err != nil {
		return nil, err
	}
	klet.admitHandlers.AddPodAdmitHandler(sysctlsAllowlist)

	// enable active deadline handler
	activeDeadlineHandler, err := newActiveDeadlineHandler(klet.statusManager, kubeDeps.Recorder, klet.clock)
	if err != nil {
		return nil, err
	}
	klet.AddPodSyncLoopHandler(activeDeadlineHandler)
	klet.AddPodSyncHandler(activeDeadlineHandler)

	klet.admitHandlers.AddPodAdmitHandler(klet.containerManager.GetAllocateResourcesPodAdmitHandler())

	criticalPodAdmissionHandler := preemption.NewCriticalPodAdmissionHandler(klet.GetActivePods, killPodNow(klet.podWorkers, kubeDeps.Recorder), kubeDeps.Recorder)
	klet.admitHandlers.AddPodAdmitHandler(lifecycle.NewPredicateAdmitHandler(klet.getNodeAnyWay, criticalPodAdmissionHandler, klet.containerManager.UpdatePluginResources))
	// apply functional Option's
	for _, opt := range kubeDeps.Options {
		opt(klet)
	}

	if sysruntime.GOOS == "linux" {
		// AppArmor is a Linux kernel security module and it does not support other operating systems.
		klet.appArmorValidator = apparmor.NewValidator()
		klet.softAdmitHandlers.AddPodAdmitHandler(lifecycle.NewAppArmorAdmitHandler(klet.appArmorValidator))
	}

	leaseDuration := time.Duration(kubeCfg.NodeLeaseDurationSeconds) * time.Second
	renewInterval := time.Duration(float64(leaseDuration) * nodeLeaseRenewIntervalFraction)
	klet.nodeLeaseController = lease.NewController(
		klet.clock,
		klet.heartbeatClient,
		string(klet.nodeName),
		kubeCfg.NodeLeaseDurationSeconds,
		klet.onRepeatedHeartbeatFailure,
		renewInterval,
		string(klet.nodeName),
		v1.NamespaceNodeLease,
		util.SetNodeOwnerFunc(klet.heartbeatClient, string(klet.nodeName)))

	// setup node shutdown manager
	shutdownManager, shutdownAdmitHandler := nodeshutdown.NewManager(&nodeshutdown.Config{
		Logger:                           logger,
		ProbeManager:                     klet.probeManager,
		Recorder:                         kubeDeps.Recorder,
		NodeRef:                          nodeRef,
		GetPodsFunc:                      klet.GetActivePods,
		KillPodFunc:                      killPodNow(klet.podWorkers, kubeDeps.Recorder),
		SyncNodeStatusFunc:               klet.syncNodeStatus,
		ShutdownGracePeriodRequested:     kubeCfg.ShutdownGracePeriod.Duration,
		ShutdownGracePeriodCriticalPods:  kubeCfg.ShutdownGracePeriodCriticalPods.Duration,
		ShutdownGracePeriodByPodPriority: kubeCfg.ShutdownGracePeriodByPodPriority,
		StateDirectory:                   rootDirectory,
	})
	klet.shutdownManager = shutdownManager
	klet.usernsManager, err = MakeUserNsManager(klet)
	if err != nil {
		return nil, err
	}
	klet.admitHandlers.AddPodAdmitHandler(shutdownAdmitHandler)

	// Finally, put the most recent version of the config on the Kubelet, so
	// people can see how it was configured.
	klet.kubeletConfiguration = *kubeCfg

	// Generating the status funcs should be the last thing we do,
	// since this relies on the rest of the Kubelet having been constructed.
	klet.setNodeStatusFuncs = klet.defaultNodeStatusFuncs()

	return klet, nil
}

type serviceLister interface {
	List(labels.Selector) ([]*v1.Service, error)
}

// Kubelet is the main kubelet implementation.
type Kubelet struct {
	kubeletConfiguration kubeletconfiginternal.KubeletConfiguration

	// hostname is the hostname the kubelet detected or was given via flag/config
	hostname string
	// hostnameOverridden indicates the hostname was overridden via flag/config
	hostnameOverridden bool

	nodeName        types.NodeName
	runtimeCache    kubecontainer.RuntimeCache
	kubeClient      clientset.Interface
	heartbeatClient clientset.Interface
	rootDirectory   string

	lastObservedNodeAddressesMux sync.RWMutex
	lastObservedNodeAddresses    []v1.NodeAddress

	// onRepeatedHeartbeatFailure is called when a heartbeat operation fails more than once. optional.
	onRepeatedHeartbeatFailure func()

	// podWorkers handle syncing Pods in response to events.
	podWorkers PodWorkers

	// resyncInterval is the interval between periodic full reconciliations of
	// pods on this node.
	resyncInterval time.Duration

	// sourcesReady records the sources seen by the kubelet, it is thread-safe.
	sourcesReady config.SourcesReady

	// podManager is a facade that abstracts away the various sources of pods
	// this Kubelet services.
	podManager kubepod.Manager

	// Needed to observe and respond to situations that could impact node stability
	evictionManager eviction.Manager

	// Optional, defaults to /logs/ from /var/log
	logServer http.Handler
	// Optional, defaults to simple Docker implementation
	runner kubecontainer.CommandRunner

	// cAdvisor used for container information.
	cadvisor cadvisor.Interface

	// Set to true to have the node register itself with the apiserver.
	registerNode bool
	// List of taints to add to a node object when the kubelet registers itself.
	registerWithTaints []v1.Taint
	// Set to true to have the node register itself as schedulable.
	registerSchedulable bool
	// for internal book keeping; access only from within registerWithApiserver
	registrationCompleted bool

	// dnsConfigurer is used for setting up DNS resolver configuration when launching pods.
	dnsConfigurer *dns.Configurer

	// masterServiceNamespace is the namespace that the master service is exposed in.
	masterServiceNamespace string
	// serviceLister knows how to list services
	serviceLister serviceLister
	// serviceHasSynced indicates whether services have been sync'd at least once.
	// Check this before trusting a response from the lister.
	serviceHasSynced cache.InformerSynced
	// nodeLister knows how to list nodes
	nodeLister corelisters.NodeLister
	// nodeHasSynced indicates whether nodes have been sync'd at least once.
	// Check this before trusting a response from the node lister.
	nodeHasSynced cache.InformerSynced
	// a list of node labels to register
	nodeLabels map[string]string

	// Last timestamp when runtime responded on ping.
	// Mutex is used to protect this value.
	runtimeState *runtimeState

	// Volume plugins.
	volumePluginMgr *volume.VolumePluginMgr

	// Handles container probing.
	probeManager prober.Manager
	// Manages container health check results.
	livenessManager  proberesults.Manager
	readinessManager proberesults.Manager
	startupManager   proberesults.Manager

	// How long to keep idle streaming command execution/port forwarding
	// connections open before terminating them
	streamingConnectionIdleTimeout time.Duration

	// The EventRecorder to use
	recorder record.EventRecorder

	// Policy for handling garbage collection of dead containers.
	containerGC kubecontainer.GC

	// Manager for image garbage collection.
	imageManager images.ImageGCManager

	// Manager for container logs.
	containerLogManager logs.ContainerLogManager

	// Secret manager.
	secretManager secret.Manager

	// ConfigMap manager.
	configMapManager configmap.Manager

	// Cached MachineInfo returned by cadvisor.
	machineInfoLock sync.RWMutex
	machineInfo     *cadvisorapi.MachineInfo

	// Handles certificate rotations.
	serverCertificateManager certificate.Manager

	// Syncs pods statuses with apiserver; also used as a cache of statuses.
	statusManager status.Manager

	// VolumeManager runs a set of asynchronous loops that figure out which
	// volumes need to be attached/mounted/unmounted/detached based on the pods
	// scheduled on this node and makes it so.
	volumeManager volumemanager.VolumeManager

	// Cloud provider interface.
	cloud cloudprovider.Interface
	// Handles requests to cloud provider with timeout
	cloudResourceSyncManager cloudresource.SyncManager

	// Indicates that the node initialization happens in an external cloud controller
	externalCloudProvider bool
	// Reference to this node.
	nodeRef *v1.ObjectReference

	// Container runtime.
	containerRuntime kubecontainer.Runtime

	// Streaming runtime handles container streaming.
	streamingRuntime kubecontainer.StreamingRuntime

	// Container runtime service (needed by container runtime Start()).
	runtimeService internalapi.RuntimeService

	// reasonCache caches the failure reason of the last creation of all containers, which is
	// used for generating ContainerStatus.
	reasonCache *ReasonCache

	// containerRuntimeReadyExpected indicates whether container runtime being ready is expected
	// so errors are logged without verbosity guard, to avoid excessive error logs at node startup.
	// It's false during the node initialization period of nodeReadyGracePeriod, and after that
	// it's set to true by fastStatusUpdateOnce when it exits.
	containerRuntimeReadyExpected bool

	// nodeStatusUpdateFrequency specifies how often kubelet computes node status. If node lease
	// feature is not enabled, it is also the frequency that kubelet posts node status to master.
	// In that case, be cautious when changing the constant, it must work with nodeMonitorGracePeriod
	// in nodecontroller. There are several constraints:
	// 1. nodeMonitorGracePeriod must be N times more than nodeStatusUpdateFrequency, where
	//    N means number of retries allowed for kubelet to post node status. It is pointless
	//    to make nodeMonitorGracePeriod be less than nodeStatusUpdateFrequency, since there
	//    will only be fresh values from Kubelet at an interval of nodeStatusUpdateFrequency.
	//    The constant must be less than podEvictionTimeout.
	// 2. nodeStatusUpdateFrequency needs to be large enough for kubelet to generate node
	//    status. Kubelet may fail to update node status reliably if the value is too small,
	//    as it takes time to gather all necessary node information.
	nodeStatusUpdateFrequency time.Duration

	// nodeStatusReportFrequency is the frequency that kubelet posts node
	// status to master. It is only used when node lease feature is enabled.
	nodeStatusReportFrequency time.Duration

	// lastStatusReportTime is the time when node status was last reported.
	lastStatusReportTime time.Time

	// syncNodeStatusMux is a lock on updating the node status, because this path is not thread-safe.
	// This lock is used by Kubelet.syncNodeStatus and Kubelet.fastNodeStatusUpdate functions and shouldn't be used anywhere else.
	syncNodeStatusMux sync.Mutex

	// updatePodCIDRMux is a lock on updating pod CIDR, because this path is not thread-safe.
	// This lock is used by Kubelet.updatePodCIDR function and shouldn't be used anywhere else.
	updatePodCIDRMux sync.Mutex

	// updateRuntimeMux is a lock on updating runtime, because this path is not thread-safe.
	// This lock is used by Kubelet.updateRuntimeUp and Kubelet.fastNodeStatusUpdate functions and shouldn't be used anywhere else.
	updateRuntimeMux sync.Mutex

	// nodeLeaseController claims and renews the node lease for this Kubelet
	nodeLeaseController lease.Controller

	// Generates pod events.
	pleg pleg.PodLifecycleEventGenerator

	// Evented PLEG
	eventedPleg pleg.PodLifecycleEventGenerator

	// Store kubecontainer.PodStatus for all pods.
	podCache kubecontainer.Cache

	// os is a facade for various syscalls that need to be mocked during testing.
	os kubecontainer.OSInterface

	// Watcher of out of memory events.
	oomWatcher oomwatcher.Watcher

	// Monitor resource usage
	resourceAnalyzer serverstats.ResourceAnalyzer

	// Whether or not we should have the QOS cgroup hierarchy for resource management
	cgroupsPerQOS bool

	// If non-empty, pass this to the container runtime as the root cgroup.
	cgroupRoot string

	// Mounter to use for volumes.
	mounter mount.Interface

	// hostutil to interact with filesystems
	hostutil hostutil.HostUtils

	// subpather to execute subpath actions
	subpather subpath.Interface

	// Manager of non-Runtime containers.
	containerManager cm.ContainerManager

	// Maximum Number of Pods which can be run by this Kubelet
	maxPods int

	// Monitor Kubelet's sync loop
	syncLoopMonitor atomic.Value

	// Container restart Backoff
	backOff *flowcontrol.Backoff

	// Information about the ports which are opened by daemons on Node running this Kubelet server.
	daemonEndpoints *v1.NodeDaemonEndpoints

	// A queue used to trigger pod workers.
	workQueue queue.WorkQueue

	// oneTimeInitializer is used to initialize modules that are dependent on the runtime to be up.
	oneTimeInitializer sync.Once

	// If set, use this IP address or addresses for the node
	nodeIPs []net.IP

	// use this function to validate the kubelet nodeIP
	nodeIPValidator func(net.IP) error

	// If non-nil, this is a unique identifier for the node in an external database, eg. cloudprovider
	providerID string

	// clock is an interface that provides time related functionality in a way that makes it
	// easy to test the code.
	clock clock.WithTicker

	// handlers called during the tryUpdateNodeStatus cycle
	setNodeStatusFuncs []func(context.Context, *v1.Node) error

	lastNodeUnschedulableLock sync.Mutex
	// maintains Node.Spec.Unschedulable value from previous run of tryUpdateNodeStatus()
	lastNodeUnschedulable bool

	// the list of handlers to call during pod admission.
	admitHandlers lifecycle.PodAdmitHandlers

	// softAdmithandlers are applied to the pod after it is admitted by the Kubelet, but before it is
	// run. A pod rejected by a softAdmitHandler will be left in a Pending state indefinitely. If a
	// rejected pod should not be recreated, or the scheduler is not aware of the rejection rule, the
	// admission rule should be applied by a softAdmitHandler.
	softAdmitHandlers lifecycle.PodAdmitHandlers

	// the list of handlers to call during pod sync loop.
	lifecycle.PodSyncLoopHandlers

	// the list of handlers to call during pod sync.
	lifecycle.PodSyncHandlers

	// the number of allowed pods per core
	podsPerCore int

	// enableControllerAttachDetach indicates the Attach/Detach controller
	// should manage attachment/detachment of volumes scheduled to this node,
	// and disable kubelet from executing any attach/detach operations
	enableControllerAttachDetach bool

	// trigger deleting containers in a pod
	containerDeletor *podContainerDeletor

	// config iptables util rules
	makeIPTablesUtilChains bool

	// The bit of the fwmark space to mark packets for SNAT.
	iptablesMasqueradeBit int

	// The bit of the fwmark space to mark packets for dropping.
	iptablesDropBit int

	// The AppArmor validator for checking whether AppArmor is supported.
	appArmorValidator apparmor.Validator

	// experimentalHostUserNamespaceDefaulting sets userns=true when users request host namespaces (pid, ipc, net),
	// are using non-namespaced capabilities (mknod, sys_time, sys_module), the pod contains a privileged container,
	// or using host path volumes.
	// This should only be enabled when the container runtime is performing user remapping AND if the
	// experimental behavior is desired.
	experimentalHostUserNamespaceDefaulting bool

	// StatsProvider provides the node and the container stats.
	StatsProvider *stats.Provider

	// This flag, if set, instructs the kubelet to keep volumes from terminated pods mounted to the node.
	// This can be useful for debugging volume related issues.
	keepTerminatedPodVolumes bool // DEPRECATED

	// pluginmanager runs a set of asynchronous loops that figure out which
	// plugins need to be registered/unregistered based on this node and makes it so.
	pluginManager pluginmanager.PluginManager

	// This flag sets a maximum number of images to report in the node status.
	nodeStatusMaxImages int32

	// Handles RuntimeClass objects for the Kubelet.
	runtimeClassManager *runtimeclass.Manager

	// Handles node shutdown events for the Node.
	shutdownManager nodeshutdown.Manager

	// Manage user namespaces
	usernsManager *usernsManager
}

// ListPodStats is delegated to StatsProvider, which implements stats.Provider interface
func (kl *Kubelet) ListPodStats(ctx context.Context) ([]statsapi.PodStats, error) {
	return kl.StatsProvider.ListPodStats(ctx)
}

// ListPodCPUAndMemoryStats is delegated to StatsProvider, which implements stats.Provider interface
func (kl *Kubelet) ListPodCPUAndMemoryStats(ctx context.Context) ([]statsapi.PodStats, error) {
	return kl.StatsProvider.ListPodCPUAndMemoryStats(ctx)
}

// ListPodStatsAndUpdateCPUNanoCoreUsage is delegated to StatsProvider, which implements stats.Provider interface
func (kl *Kubelet) ListPodStatsAndUpdateCPUNanoCoreUsage(ctx context.Context) ([]statsapi.PodStats, error) {
	return kl.StatsProvider.ListPodStatsAndUpdateCPUNanoCoreUsage(ctx)
}

// ImageFsStats is delegated to StatsProvider, which implements stats.Provider interface
func (kl *Kubelet) ImageFsStats(ctx context.Context) (*statsapi.FsStats, error) {
	return kl.StatsProvider.ImageFsStats(ctx)
}

// GetCgroupStats is delegated to StatsProvider, which implements stats.Provider interface
func (kl *Kubelet) GetCgroupStats(cgroupName string, updateStats bool) (*statsapi.ContainerStats, *statsapi.NetworkStats, error) {
	return kl.StatsProvider.GetCgroupStats(cgroupName, updateStats)
}

// GetCgroupCPUAndMemoryStats is delegated to StatsProvider, which implements stats.Provider interface
func (kl *Kubelet) GetCgroupCPUAndMemoryStats(cgroupName string, updateStats bool) (*statsapi.ContainerStats, error) {
	return kl.StatsProvider.GetCgroupCPUAndMemoryStats(cgroupName, updateStats)
}

// RootFsStats is delegated to StatsProvider, which implements stats.Provider interface
func (kl *Kubelet) RootFsStats() (*statsapi.FsStats, error) {
	return kl.StatsProvider.RootFsStats()
}

// GetContainerInfo is delegated to StatsProvider, which implements stats.Provider interface
func (kl *Kubelet) GetContainerInfo(ctx context.Context, podFullName string, uid types.UID, containerName string, req *cadvisorapi.ContainerInfoRequest) (*cadvisorapi.ContainerInfo, error) {
	return kl.StatsProvider.GetContainerInfo(ctx, podFullName, uid, containerName, req)
}

// GetRawContainerInfo is delegated to StatsProvider, which implements stats.Provider interface
func (kl *Kubelet) GetRawContainerInfo(containerName string, req *cadvisorapi.ContainerInfoRequest, subcontainers bool) (map[string]*cadvisorapi.ContainerInfo, error) {
	return kl.StatsProvider.GetRawContainerInfo(containerName, req, subcontainers)
}

// RlimitStats is delegated to StatsProvider, which implements stats.Provider interface
func (kl *Kubelet) RlimitStats() (*statsapi.RlimitStats, error) {
	return kl.StatsProvider.RlimitStats()
}

// setupDataDirs creates:
// 1.  the root directory
// 2.  the pods directory
// 3.  the plugins directory
// 4.  the pod-resources directory
// 5.  the checkpoint directory
func (kl *Kubelet) setupDataDirs() error {
	kl.rootDirectory = path.Clean(kl.rootDirectory)
	pluginRegistrationDir := kl.getPluginsRegistrationDir()
	pluginsDir := kl.getPluginsDir()
	if err := os.MkdirAll(kl.getRootDir(), 0750); err != nil {
		return fmt.Errorf("error creating root directory: %v", err)
	}
	if err := kl.hostutil.MakeRShared(kl.getRootDir()); err != nil {
		return fmt.Errorf("error configuring root directory: %v", err)
	}
	if err := os.MkdirAll(kl.getPodsDir(), 0750); err != nil {
		return fmt.Errorf("error creating pods directory: %v", err)
	}
	if err := os.MkdirAll(kl.getPluginsDir(), 0750); err != nil {
		return fmt.Errorf("error creating plugins directory: %v", err)
	}
	if err := os.MkdirAll(kl.getPluginsRegistrationDir(), 0750); err != nil {
		return fmt.Errorf("error creating plugins registry directory: %v", err)
	}
	if err := os.MkdirAll(kl.getPodResourcesDir(), 0750); err != nil {
		return fmt.Errorf("error creating podresources directory: %v", err)
	}
	if utilfeature.DefaultFeatureGate.Enabled(features.ContainerCheckpoint) {
		if err := os.MkdirAll(kl.getCheckpointsDir(), 0700); err != nil {
			return fmt.Errorf("error creating checkpoint directory: %v", err)
		}
	}
	if selinux.GetEnabled() {
		err := selinux.SetFileLabel(pluginRegistrationDir, config.KubeletPluginsDirSELinuxLabel)
		if err != nil {
			klog.InfoS("Unprivileged containerized plugins might not work, could not set selinux context on plugin registration dir", "path", pluginRegistrationDir, "err", err)
		}
		err = selinux.SetFileLabel(pluginsDir, config.KubeletPluginsDirSELinuxLabel)
		if err != nil {
			klog.InfoS("Unprivileged containerized plugins might not work, could not set selinux context on plugins dir", "path", pluginsDir, "err", err)
		}
	}
	return nil
}

// StartGarbageCollection starts garbage collection threads.
func (kl *Kubelet) StartGarbageCollection() {
	loggedContainerGCFailure := false
	go wait.Until(func() {
		ctx := context.Background()
		if err := kl.containerGC.GarbageCollect(ctx); err != nil {
			klog.ErrorS(err, "Container garbage collection failed")
			kl.recorder.Eventf(kl.nodeRef, v1.EventTypeWarning, events.ContainerGCFailed, err.Error())
			loggedContainerGCFailure = true
		} else {
			var vLevel klog.Level = 4
			if loggedContainerGCFailure {
				vLevel = 1
				loggedContainerGCFailure = false
			}

			klog.V(vLevel).InfoS("Container garbage collection succeeded")
		}
	}, ContainerGCPeriod, wait.NeverStop)

	// when the high threshold is set to 100, stub the image GC manager
	if kl.kubeletConfiguration.ImageGCHighThresholdPercent == 100 {
		klog.V(2).InfoS("ImageGCHighThresholdPercent is set 100, Disable image GC")
		return
	}

	prevImageGCFailed := false
	go wait.Until(func() {
		ctx := context.Background()
		if err := kl.imageManager.GarbageCollect(ctx); err != nil {
			if prevImageGCFailed {
				klog.ErrorS(err, "Image garbage collection failed multiple times in a row")
				// Only create an event for repeated failures
				kl.recorder.Eventf(kl.nodeRef, v1.EventTypeWarning, events.ImageGCFailed, err.Error())
			} else {
				klog.ErrorS(err, "Image garbage collection failed once. Stats initialization may not have completed yet")
			}
			prevImageGCFailed = true
		} else {
			var vLevel klog.Level = 4
			if prevImageGCFailed {
				vLevel = 1
				prevImageGCFailed = false
			}

			klog.V(vLevel).InfoS("Image garbage collection succeeded")
		}
	}, ImageGCPeriod, wait.NeverStop)
}

// initializeModules will initialize internal modules that do not require the container runtime to be up.
// Note that the modules here must not depend on modules that are not initialized here.
func (kl *Kubelet) initializeModules() error {
	// Prometheus metrics.
	metrics.Register(
		collectors.NewVolumeStatsCollector(kl),
		collectors.NewLogMetricsCollector(kl.StatsProvider.ListPodStats),
	)
	metrics.SetNodeName(kl.nodeName)
	servermetrics.Register()

	// Setup filesystem directories.
	if err := kl.setupDataDirs(); err != nil {
		return err
	}

	// If the container logs directory does not exist, create it.
	if _, err := os.Stat(ContainerLogsDir); err != nil {
		if err := kl.os.MkdirAll(ContainerLogsDir, 0755); err != nil {
			return fmt.Errorf("failed to create directory %q: %v", ContainerLogsDir, err)
		}
	}

	// Start the image manager.
	kl.imageManager.Start()

	// Start the certificate manager if it was enabled.
	if kl.serverCertificateManager != nil {
		kl.serverCertificateManager.Start()
	}

	// Start out of memory watcher.
	if kl.oomWatcher != nil {
		if err := kl.oomWatcher.Start(kl.nodeRef); err != nil {
			return fmt.Errorf("failed to start OOM watcher: %w", err)
		}
	}

	// Start resource analyzer
	kl.resourceAnalyzer.Start()

	return nil
}

// initializeRuntimeDependentModules will initialize internal modules that require the container runtime to be up.
func (kl *Kubelet) initializeRuntimeDependentModules() {
	if err := kl.cadvisor.Start(); err != nil {
		// Fail kubelet and rely on the babysitter to retry starting kubelet.
		klog.ErrorS(err, "Failed to start cAdvisor")
		os.Exit(1)
	}

	// trigger on-demand stats collection once so that we have capacity information for ephemeral storage.
	// ignore any errors, since if stats collection is not successful, the container manager will fail to start below.
	kl.StatsProvider.GetCgroupStats("/", true)
	// Start container manager.
	node, err := kl.getNodeAnyWay()
	if err != nil {
		// Fail kubelet and rely on the babysitter to retry starting kubelet.
		klog.ErrorS(err, "Kubelet failed to get node info")
		os.Exit(1)
	}
	// containerManager must start after cAdvisor because it needs filesystem capacity information
	if err := kl.containerManager.Start(node, kl.GetActivePods, kl.sourcesReady, kl.statusManager, kl.runtimeService, kl.supportLocalStorageCapacityIsolation()); err != nil {
		// Fail kubelet and rely on the babysitter to retry starting kubelet.
		klog.ErrorS(err, "Failed to start ContainerManager")
		os.Exit(1)
	}
	// eviction manager must start after cadvisor because it needs to know if the container runtime has a dedicated imagefs
	kl.evictionManager.Start(kl.StatsProvider, kl.GetActivePods, kl.podResourcesAreReclaimed, evictionMonitoringPeriod)

	// container log manager must start after container runtime is up to retrieve information from container runtime
	// and inform container to reopen log file after log rotation.
	kl.containerLogManager.Start()
	// Adding Registration Callback function for CSI Driver
	kl.pluginManager.AddHandler(pluginwatcherapi.CSIPlugin, plugincache.PluginHandler(csi.PluginHandler))
	// Adding Registration Callback function for DRA Plugin
	if utilfeature.DefaultFeatureGate.Enabled(features.DynamicResourceAllocation) {
		kl.pluginManager.AddHandler(pluginwatcherapi.DRAPlugin, plugincache.PluginHandler(draplugin.NewRegistrationHandler()))
	}
	// Adding Registration Callback function for Device Manager
	kl.pluginManager.AddHandler(pluginwatcherapi.DevicePlugin, kl.containerManager.GetPluginRegistrationHandler())

	// Start the plugin manager
	klog.V(4).InfoS("Starting plugin manager")
	go kl.pluginManager.Run(kl.sourcesReady, wait.NeverStop)

	err = kl.shutdownManager.Start()
	if err != nil {
		// The shutdown manager is not critical for kubelet, so log failure, but don't block Kubelet startup if there was a failure starting it.
		klog.ErrorS(err, "Failed to start node shutdown manager")
	}
}

// Run starts the kubelet reacting to config updates
func (kl *Kubelet) Run(updates <-chan kubetypes.PodUpdate) {
	ctx := context.Background()
	if kl.logServer == nil {
		kl.logServer = http.StripPrefix("/logs/", http.FileServer(http.Dir("/var/log/")))
	}
	if kl.kubeClient == nil {
		klog.InfoS("No API server defined - no node status update will be sent")
	}

	// Start the cloud provider sync manager
	if kl.cloudResourceSyncManager != nil {
		go kl.cloudResourceSyncManager.Run(wait.NeverStop)
	}

	if err := kl.initializeModules(); err != nil {
		kl.recorder.Eventf(kl.nodeRef, v1.EventTypeWarning, events.KubeletSetupFailed, err.Error())
		klog.ErrorS(err, "Failed to initialize internal modules")
		os.Exit(1)
	}

	// Start volume manager
	go kl.volumeManager.Run(kl.sourcesReady, wait.NeverStop)

	if kl.kubeClient != nil {
		// Start two go-routines to update the status.
		//
		// The first will report to the apiserver every nodeStatusUpdateFrequency and is aimed to provide regular status intervals,
		// while the second is used to provide a more timely status update during initialization and runs an one-shot update to the apiserver
		// once the node becomes ready, then exits afterwards.
		//
		// Introduce some small jittering to ensure that over time the requests won't start
		// accumulating at approximately the same time from the set of nodes due to priority and
		// fairness effect.
		go wait.JitterUntil(kl.syncNodeStatus, kl.nodeStatusUpdateFrequency, 0.04, true, wait.NeverStop)
		go kl.fastStatusUpdateOnce()

		// start syncing lease
		go kl.nodeLeaseController.Run(wait.NeverStop)
	}
	go wait.Until(kl.updateRuntimeUp, 5*time.Second, wait.NeverStop)

	// Set up iptables util rules
	if kl.makeIPTablesUtilChains {
		kl.initNetworkUtil()
	}

	// Start component sync loops.
	kl.statusManager.Start()

	// Start syncing RuntimeClasses if enabled.
	if kl.runtimeClassManager != nil {
		kl.runtimeClassManager.Start(wait.NeverStop)
	}

	// Start the pod lifecycle event generator.
	kl.pleg.Start()

	// Start eventedPLEG only if EventedPLEG feature gate is enabled.
	if utilfeature.DefaultFeatureGate.Enabled(features.EventedPLEG) {
		kl.eventedPleg.Start()
	}

	kl.syncLoop(ctx, updates, kl)
}

// syncPod is the transaction script for the sync of a single pod (setting up)
// a pod. This method is reentrant and expected to converge a pod towards the
// desired state of the spec. The reverse (teardown) is handled in
// syncTerminatingPod and syncTerminatedPod. If syncPod exits without error,
// then the pod runtime state is in sync with the desired configuration state
// (pod is running). If syncPod exits with a transient error, the next
// invocation of syncPod is expected to make progress towards reaching the
// runtime state. syncPod exits with isTerminal when the pod was detected to
// have reached a terminal lifecycle phase due to container exits (for
// RestartNever or RestartOnFailure) and the next method invoked will by
// syncTerminatingPod.
//
// Arguments:
//
// updateType - whether this is a create (first time) or an update, should
//
//	only be used for metrics since this method must be reentrant
//
// pod - the pod that is being set up
// mirrorPod - the mirror pod known to the kubelet for this pod, if any
// podStatus - the most recent pod status observed for this pod which can
//
//	be used to determine the set of actions that should be taken during
//	this loop of syncPod
//
// The workflow is:
//   - If the pod is being created, record pod worker start latency
//   - Call generateAPIPodStatus to prepare an v1.PodStatus for the pod
//   - If the pod is being seen as running for the first time, record pod
//     start latency
//   - Update the status of the pod in the status manager
//   - Stop the pod's containers if it should not be running due to soft
//     admission
//   - Ensure any background tracking for a runnable pod is started
//   - Create a mirror pod if the pod is a static pod, and does not
//     already have a mirror pod
//   - Create the data directories for the pod if they do not exist
//   - Wait for volumes to attach/mount
//   - Fetch the pull secrets for the pod
//   - Call the container runtime's SyncPod callback
//   - Update the traffic shaping for the pod's ingress and egress limits
//
// If any step of this workflow errors, the error is returned, and is repeated
// on the next syncPod call.
//
// This operation writes all events that are dispatched in order to provide
// the most accurate information possible about an error situation to aid debugging.
// Callers should not write an event if this operation returns an error.
func (kl *Kubelet) syncPod(_ context.Context, updateType kubetypes.SyncPodType, pod, mirrorPod *v1.Pod, podStatus *kubecontainer.PodStatus) (isTerminal bool, err error) {
	// TODO(#113606): connect this with the incoming context parameter, which comes from the pod worker.
	// Currently, using that context causes test failures.
	ctx := context.TODO()
	klog.V(4).InfoS("syncPod enter", "pod", klog.KObj(pod), "podUID", pod.UID)
	defer func() {
		klog.V(4).InfoS("syncPod exit", "pod", klog.KObj(pod), "podUID", pod.UID, "isTerminal", isTerminal)
	}()

	// Latency measurements for the main workflow are relative to the
	// first time the pod was seen by kubelet.
	var firstSeenTime time.Time
	if firstSeenTimeStr, ok := pod.Annotations[kubetypes.ConfigFirstSeenAnnotationKey]; ok {
		firstSeenTime = kubetypes.ConvertToTimestamp(firstSeenTimeStr).Get()
	}

	// Record pod worker start latency if being created
	// TODO: make pod workers record their own latencies
	if updateType == kubetypes.SyncPodCreate {
		if !firstSeenTime.IsZero() {
			// This is the first time we are syncing the pod. Record the latency
			// since kubelet first saw the pod if firstSeenTime is set.
			metrics.PodWorkerStartDuration.Observe(metrics.SinceInSeconds(firstSeenTime))
		} else {
			klog.V(3).InfoS("First seen time not recorded for pod",
				"podUID", pod.UID,
				"pod", klog.KObj(pod))
		}
	}

	// Generate final API pod status with pod and status manager status
	apiPodStatus := kl.generateAPIPodStatus(pod, podStatus)
	// The pod IP may be changed in generateAPIPodStatus if the pod is using host network. (See #24576)
	// TODO(random-liu): After writing pod spec into container labels, check whether pod is using host network, and
	// set pod IP to hostIP directly in runtime.GetPodStatus
	podStatus.IPs = make([]string, 0, len(apiPodStatus.PodIPs))
	for _, ipInfo := range apiPodStatus.PodIPs {
		podStatus.IPs = append(podStatus.IPs, ipInfo.IP)
	}
	if len(podStatus.IPs) == 0 && len(apiPodStatus.PodIP) > 0 {
		podStatus.IPs = []string{apiPodStatus.PodIP}
	}

	// If the pod is terminal, we don't need to continue to setup the pod
	if apiPodStatus.Phase == v1.PodSucceeded || apiPodStatus.Phase == v1.PodFailed {
		kl.statusManager.SetPodStatus(pod, apiPodStatus)
		isTerminal = true
		return isTerminal, nil
	}

	// If the pod should not be running, we request the pod's containers be stopped. This is not the same
	// as termination (we want to stop the pod, but potentially restart it later if soft admission allows
	// it later). Set the status and phase appropriately
	runnable := kl.canRunPod(pod)
	if !runnable.Admit {
		// Pod is not runnable; and update the Pod and Container statuses to why.
		if apiPodStatus.Phase != v1.PodFailed && apiPodStatus.Phase != v1.PodSucceeded {
			apiPodStatus.Phase = v1.PodPending
		}
		apiPodStatus.Reason = runnable.Reason
		apiPodStatus.Message = runnable.Message
		// Waiting containers are not creating.
		const waitingReason = "Blocked"
		for _, cs := range apiPodStatus.InitContainerStatuses {
			if cs.State.Waiting != nil {
				cs.State.Waiting.Reason = waitingReason
			}
		}
		for _, cs := range apiPodStatus.ContainerStatuses {
			if cs.State.Waiting != nil {
				cs.State.Waiting.Reason = waitingReason
			}
		}
	}

	// Record the time it takes for the pod to become running
	// since kubelet first saw the pod if firstSeenTime is set.
	existingStatus, ok := kl.statusManager.GetPodStatus(pod.UID)
	if !ok || existingStatus.Phase == v1.PodPending && apiPodStatus.Phase == v1.PodRunning &&
		!firstSeenTime.IsZero() {
		metrics.PodStartDuration.Observe(metrics.SinceInSeconds(firstSeenTime))
	}

	kl.statusManager.SetPodStatus(pod, apiPodStatus)

	// Pods that are not runnable must be stopped - return a typed error to the pod worker
	if !runnable.Admit {
		klog.V(2).InfoS("Pod is not runnable and must have running containers stopped", "pod", klog.KObj(pod), "podUID", pod.UID, "message", runnable.Message)
		var syncErr error
		p := kubecontainer.ConvertPodStatusToRunningPod(kl.getRuntime().Type(), podStatus)
		if err := kl.killPod(ctx, pod, p, nil); err != nil {
			kl.recorder.Eventf(pod, v1.EventTypeWarning, events.FailedToKillPod, "error killing pod: %v", err)
			syncErr = fmt.Errorf("error killing pod: %v", err)
			utilruntime.HandleError(syncErr)
		} else {
			// There was no error killing the pod, but the pod cannot be run.
			// Return an error to signal that the sync loop should back off.
			syncErr = fmt.Errorf("pod cannot be run: %s", runnable.Message)
		}
		return false, syncErr
	}

	// If the network plugin is not ready, only start the pod if it uses the host network
	if err := kl.runtimeState.networkErrors(); err != nil && !kubecontainer.IsHostNetworkPod(pod) {
		kl.recorder.Eventf(pod, v1.EventTypeWarning, events.NetworkNotReady, "%s: %v", NetworkNotReadyErrorMsg, err)
		return false, fmt.Errorf("%s: %v", NetworkNotReadyErrorMsg, err)
	}

	// ensure the kubelet knows about referenced secrets or configmaps used by the pod
	if !kl.podWorkers.IsPodTerminationRequested(pod.UID) {
		if kl.secretManager != nil {
			kl.secretManager.RegisterPod(pod)
		}
		if kl.configMapManager != nil {
			kl.configMapManager.RegisterPod(pod)
		}
	}

	// Create Cgroups for the pod and apply resource parameters
	// to them if cgroups-per-qos flag is enabled.
	pcm := kl.containerManager.NewPodContainerManager()
	// If pod has already been terminated then we need not create
	// or update the pod's cgroup
	// TODO: once context cancellation is added this check can be removed
	if !kl.podWorkers.IsPodTerminationRequested(pod.UID) {
		// When the kubelet is restarted with the cgroups-per-qos
		// flag enabled, all the pod's running containers
		// should be killed intermittently and brought back up
		// under the qos cgroup hierarchy.
		// Check if this is the pod's first sync
		firstSync := true
		for _, containerStatus := range apiPodStatus.ContainerStatuses {
			if containerStatus.State.Running != nil {
				firstSync = false
				break
			}
		}
		// Don't kill containers in pod if pod's cgroups already
		// exists or the pod is running for the first time
		podKilled := false
		if !pcm.Exists(pod) && !firstSync {
			p := kubecontainer.ConvertPodStatusToRunningPod(kl.getRuntime().Type(), podStatus)
			if err := kl.killPod(ctx, pod, p, nil); err == nil {
				podKilled = true
			} else {
				klog.ErrorS(err, "KillPod failed", "pod", klog.KObj(pod), "podStatus", podStatus)
			}
		}
		// Create and Update pod's Cgroups
		// Don't create cgroups for run once pod if it was killed above
		// The current policy is not to restart the run once pods when
		// the kubelet is restarted with the new flag as run once pods are
		// expected to run only once and if the kubelet is restarted then
		// they are not expected to run again.
		// We don't create and apply updates to cgroup if its a run once pod and was killed above
		if !(podKilled && pod.Spec.RestartPolicy == v1.RestartPolicyNever) {
			if !pcm.Exists(pod) {
				if err := kl.containerManager.UpdateQOSCgroups(); err != nil {
					klog.V(2).InfoS("Failed to update QoS cgroups while syncing pod", "pod", klog.KObj(pod), "err", err)
				}
				if err := pcm.EnsureExists(pod); err != nil {
					kl.recorder.Eventf(pod, v1.EventTypeWarning, events.FailedToCreatePodContainer, "unable to ensure pod container exists: %v", err)
					return false, fmt.Errorf("failed to ensure that the pod: %v cgroups exist and are correctly applied: %v", pod.UID, err)
				}
			}
		}
	}

	// Create Mirror Pod for Static Pod if it doesn't already exist
	if kubetypes.IsStaticPod(pod) {
		deleted := false
		if mirrorPod != nil {
			if mirrorPod.DeletionTimestamp != nil || !kl.podManager.IsMirrorPodOf(mirrorPod, pod) {
				// The mirror pod is semantically different from the static pod. Remove
				// it. The mirror pod will get recreated later.
				klog.InfoS("Trying to delete pod", "pod", klog.KObj(pod), "podUID", mirrorPod.ObjectMeta.UID)
				podFullName := kubecontainer.GetPodFullName(pod)
				var err error
				deleted, err = kl.podManager.DeleteMirrorPod(podFullName, &mirrorPod.ObjectMeta.UID)
				if deleted {
					klog.InfoS("Deleted mirror pod because it is outdated", "pod", klog.KObj(mirrorPod))
				} else if err != nil {
					klog.ErrorS(err, "Failed deleting mirror pod", "pod", klog.KObj(mirrorPod))
				}
			}
		}
		if mirrorPod == nil || deleted {
			node, err := kl.GetNode()
			if err != nil || node.DeletionTimestamp != nil {
				klog.V(4).InfoS("No need to create a mirror pod, since node has been removed from the cluster", "node", klog.KRef("", string(kl.nodeName)))
			} else {
				klog.V(4).InfoS("Creating a mirror pod for static pod", "pod", klog.KObj(pod))
				if err := kl.podManager.CreateMirrorPod(pod); err != nil {
					klog.ErrorS(err, "Failed creating a mirror pod for", "pod", klog.KObj(pod))
				}
			}
		}
	}

	// Make data directories for the pod
	if err := kl.makePodDataDirs(pod); err != nil {
		kl.recorder.Eventf(pod, v1.EventTypeWarning, events.FailedToMakePodDataDirectories, "error making pod data directories: %v", err)
		klog.ErrorS(err, "Unable to make pod data directories for pod", "pod", klog.KObj(pod))
		return false, err
	}

	// Volume manager will not mount volumes for terminating pods
	// TODO: once context cancellation is added this check can be removed
	if !kl.podWorkers.IsPodTerminationRequested(pod.UID) {
		// Wait for volumes to attach/mount
		if err := kl.volumeManager.WaitForAttachAndMount(pod); err != nil {
			kl.recorder.Eventf(pod, v1.EventTypeWarning, events.FailedMountVolume, "Unable to attach or mount volumes: %v", err)
			klog.ErrorS(err, "Unable to attach or mount volumes for pod; skipping pod", "pod", klog.KObj(pod))
			return false, err
		}
	}

	// Fetch the pull secrets for the pod
	pullSecrets := kl.getPullSecretsForPod(pod)

	// Ensure the pod is being probed
	kl.probeManager.AddPod(pod)

	// Call the container runtime's SyncPod callback
	result := kl.containerRuntime.SyncPod(ctx, pod, podStatus, pullSecrets, kl.backOff)
	kl.reasonCache.Update(pod.UID, result)
	if err := result.Error(); err != nil {
		// Do not return error if the only failures were pods in backoff
		for _, r := range result.SyncResults {
			if r.Error != kubecontainer.ErrCrashLoopBackOff && r.Error != images.ErrImagePullBackOff {
				// Do not record an event here, as we keep all event logging for sync pod failures
				// local to container runtime, so we get better errors.
				return false, err
			}
		}

		return false, nil
	}

	return false, nil
}

// syncTerminatingPod is expected to terminate all running containers in a pod. Once this method
// returns without error, the pod's local state can be safely cleaned up. If runningPod is passed,
// we perform no status updates.
func (kl *Kubelet) syncTerminatingPod(_ context.Context, pod *v1.Pod, podStatus *kubecontainer.PodStatus, runningPod *kubecontainer.Pod, gracePeriod *int64, podStatusFn func(*v1.PodStatus)) error {
	// TODO(#113606): connect this with the incoming context parameter, which comes from the pod worker.
	// Currently, using that context causes test failures.
	ctx := context.Background()
	klog.V(4).InfoS("syncTerminatingPod enter", "pod", klog.KObj(pod), "podUID", pod.UID)
	defer klog.V(4).InfoS("syncTerminatingPod exit", "pod", klog.KObj(pod), "podUID", pod.UID)

	// when we receive a runtime only pod (runningPod != nil) we don't need to update the status
	// manager or refresh the status of the cache, because a successful killPod will ensure we do
	// not get invoked again
	if runningPod != nil {
		// we kill the pod with the specified grace period since this is a termination
		if gracePeriod != nil {
			klog.V(4).InfoS("Pod terminating with grace period", "pod", klog.KObj(pod), "podUID", pod.UID, "gracePeriod", *gracePeriod)
		} else {
			klog.V(4).InfoS("Pod terminating with grace period", "pod", klog.KObj(pod), "podUID", pod.UID, "gracePeriod", nil)
		}
		if err := kl.killPod(ctx, pod, *runningPod, gracePeriod); err != nil {
			kl.recorder.Eventf(pod, v1.EventTypeWarning, events.FailedToKillPod, "error killing pod: %v", err)
			// there was an error killing the pod, so we return that error directly
			utilruntime.HandleError(err)
			return err
		}
		klog.V(4).InfoS("Pod termination stopped all running orphan containers", "pod", klog.KObj(pod), "podUID", pod.UID)
		return nil
	}

	apiPodStatus := kl.generateAPIPodStatus(pod, podStatus)
	if podStatusFn != nil {
		podStatusFn(&apiPodStatus)
	}
	kl.statusManager.SetPodStatus(pod, apiPodStatus)

	if gracePeriod != nil {
		klog.V(4).InfoS("Pod terminating with grace period", "pod", klog.KObj(pod), "podUID", pod.UID, "gracePeriod", *gracePeriod)
	} else {
		klog.V(4).InfoS("Pod terminating with grace period", "pod", klog.KObj(pod), "podUID", pod.UID, "gracePeriod", nil)
	}

	kl.probeManager.StopLivenessAndStartup(pod)

	p := kubecontainer.ConvertPodStatusToRunningPod(kl.getRuntime().Type(), podStatus)
	if err := kl.killPod(ctx, pod, p, gracePeriod); err != nil {
		kl.recorder.Eventf(pod, v1.EventTypeWarning, events.FailedToKillPod, "error killing pod: %v", err)
		// there was an error killing the pod, so we return that error directly
		utilruntime.HandleError(err)
		return err
	}

	// Once the containers are stopped, we can stop probing for liveness and readiness.
	// TODO: once a pod is terminal, certain probes (liveness exec) could be stopped immediately after
	//   the detection of a container shutdown or (for readiness) after the first failure. Tracked as
	//   https://github.com/kubernetes/kubernetes/issues/107894 although may not be worth optimizing.
	kl.probeManager.RemovePod(pod)

	// Guard against consistency issues in KillPod implementations by checking that there are no
	// running containers. This method is invoked infrequently so this is effectively free and can
	// catch race conditions introduced by callers updating pod status out of order.
	// TODO: have KillPod return the terminal status of stopped containers and write that into the
	//  cache immediately
	podStatus, err := kl.containerRuntime.GetPodStatus(ctx, pod.UID, pod.Name, pod.Namespace)
	if err != nil {
		klog.ErrorS(err, "Unable to read pod status prior to final pod termination", "pod", klog.KObj(pod), "podUID", pod.UID)
		return err
	}
	var runningContainers []string
	type container struct {
		Name       string
		State      string
		ExitCode   int
		FinishedAt string
	}
	var containers []container
	klogV := klog.V(4)
	klogVEnabled := klogV.Enabled()
	for _, s := range podStatus.ContainerStatuses {
		if s.State == kubecontainer.ContainerStateRunning {
			runningContainers = append(runningContainers, s.ID.String())
		}
		if klogVEnabled {
			containers = append(containers, container{Name: s.Name, State: string(s.State), ExitCode: s.ExitCode, FinishedAt: s.FinishedAt.UTC().Format(time.RFC3339Nano)})
		}
	}
	if klogVEnabled {
		sort.Slice(containers, func(i, j int) bool { return containers[i].Name < containers[j].Name })
		klog.V(4).InfoS("Post-termination container state", "pod", klog.KObj(pod), "podUID", pod.UID, "containers", containers)
	}
	if len(runningContainers) > 0 {
		return fmt.Errorf("detected running containers after a successful KillPod, CRI violation: %v", runningContainers)
	}

	// NOTE: resources must be unprepared AFTER all containers have stopped
	// and BEFORE the pod status is changed on the API server
	// to avoid race conditions with the resource deallocation code in kubernetes core.
	if utilfeature.DefaultFeatureGate.Enabled(features.DynamicResourceAllocation) {
		if err := kl.containerManager.UnprepareResources(pod); err != nil {
			return err
		}
	}

	// we have successfully stopped all containers, the pod is terminating, our status is "done"
	klog.V(4).InfoS("Pod termination stopped all running containers", "pod", klog.KObj(pod), "podUID", pod.UID)

	return nil
}

// syncTerminatedPod cleans up a pod that has terminated (has no running containers).
// The invocations in this call are expected to tear down what PodResourcesAreReclaimed checks (which
// gates pod deletion). When this method exits the pod is expected to be ready for cleanup.
// TODO: make this method take a context and exit early
func (kl *Kubelet) syncTerminatedPod(ctx context.Context, pod *v1.Pod, podStatus *kubecontainer.PodStatus) error {
	klog.V(4).InfoS("syncTerminatedPod enter", "pod", klog.KObj(pod), "podUID", pod.UID)
	defer klog.V(4).InfoS("syncTerminatedPod exit", "pod", klog.KObj(pod), "podUID", pod.UID)

	// generate the final status of the pod
	// TODO: should we simply fold this into TerminatePod? that would give a single pod update
	apiPodStatus := kl.generateAPIPodStatus(pod, podStatus)

	kl.statusManager.SetPodStatus(pod, apiPodStatus)

	// volumes are unmounted after the pod worker reports ShouldPodRuntimeBeRemoved (which is satisfied
	// before syncTerminatedPod is invoked)
	if err := kl.volumeManager.WaitForUnmount(pod); err != nil {
		return err
	}
	klog.V(4).InfoS("Pod termination unmounted volumes", "pod", klog.KObj(pod), "podUID", pod.UID)

	// After volume unmount is complete, let the secret and configmap managers know we're done with this pod
	if kl.secretManager != nil {
		kl.secretManager.UnregisterPod(pod)
	}
	if kl.configMapManager != nil {
		kl.configMapManager.UnregisterPod(pod)
	}

	// Note: we leave pod containers to be reclaimed in the background since dockershim requires the
	// container for retrieving logs and we want to make sure logs are available until the pod is
	// physically deleted.

	// remove any cgroups in the hierarchy for pods that are no longer running.
	if kl.cgroupsPerQOS {
		pcm := kl.containerManager.NewPodContainerManager()
		name, _ := pcm.GetPodContainerName(pod)
		if err := pcm.Destroy(name); err != nil {
			return err
		}
		klog.V(4).InfoS("Pod termination removed cgroups", "pod", klog.KObj(pod), "podUID", pod.UID)
	}

	kl.usernsManager.Release(pod.UID)

	// mark the final pod status
	kl.statusManager.TerminatePod(pod)
	klog.V(4).InfoS("Pod is terminated and will need no more status updates", "pod", klog.KObj(pod), "podUID", pod.UID)

	return nil
}

// Get pods which should be resynchronized. Currently, the following pod should be resynchronized:
//   - pod whose work is ready.
//   - internal modules that request sync of a pod.
func (kl *Kubelet) getPodsToSync() []*v1.Pod {
	allPods := kl.podManager.GetPods()
	podUIDs := kl.workQueue.GetWork()
	podUIDSet := sets.NewString()
	for _, podUID := range podUIDs {
		podUIDSet.Insert(string(podUID))
	}
	var podsToSync []*v1.Pod
	for _, pod := range allPods {
		if podUIDSet.Has(string(pod.UID)) {
			// The work of the pod is ready
			podsToSync = append(podsToSync, pod)
			continue
		}
		for _, podSyncLoopHandler := range kl.PodSyncLoopHandlers {
			if podSyncLoopHandler.ShouldSync(pod) {
				podsToSync = append(podsToSync, pod)
				break
			}
		}
	}
	return podsToSync
}

// deletePod deletes the pod from the internal state of the kubelet by:
// 1.  stopping the associated pod worker asynchronously
// 2.  signaling to kill the pod by sending on the podKillingCh channel
//
// deletePod returns an error if not all sources are ready or the pod is not
// found in the runtime cache.
func (kl *Kubelet) deletePod(pod *v1.Pod) error {
	if pod == nil {
		return fmt.Errorf("deletePod does not allow nil pod")
	}
	if !kl.sourcesReady.AllReady() {
		// If the sources aren't ready, skip deletion, as we may accidentally delete pods
		// for sources that haven't reported yet.
		return fmt.Errorf("skipping delete because sources aren't ready yet")
	}
	klog.V(3).InfoS("Pod has been deleted and must be killed", "pod", klog.KObj(pod), "podUID", pod.UID)
	kl.podWorkers.UpdatePod(UpdatePodOptions{
		Pod:        pod,
		UpdateType: kubetypes.SyncPodKill,
	})
	// We leave the volume/directory cleanup to the periodic cleanup routine.
	return nil
}

// rejectPod records an event about the pod with the given reason and message,
// and updates the pod to the failed phase in the status manage.
func (kl *Kubelet) rejectPod(pod *v1.Pod, reason, message string) {
	kl.recorder.Eventf(pod, v1.EventTypeWarning, reason, message)
	kl.statusManager.SetPodStatus(pod, v1.PodStatus{
		Phase:   v1.PodFailed,
		Reason:  reason,
		Message: "Pod was rejected: " + message})
}

// canAdmitPod determines if a pod can be admitted, and gives a reason if it
// cannot. "pod" is new pod, while "pods" are all admitted pods
// The function returns a boolean value indicating whether the pod
// can be admitted, a brief single-word reason and a message explaining why
// the pod cannot be admitted.
func (kl *Kubelet) canAdmitPod(pods []*v1.Pod, pod *v1.Pod) (bool, string, string) {
	// the kubelet will invoke each pod admit handler in sequence
	// if any handler rejects, the pod is rejected.
	// TODO: move out of disk check into a pod admitter
	// TODO: out of resource eviction should have a pod admitter call-out
	attrs := &lifecycle.PodAdmitAttributes{Pod: pod, OtherPods: pods}
	for _, podAdmitHandler := range kl.admitHandlers {
		if result := podAdmitHandler.Admit(attrs); !result.Admit {
			return false, result.Reason, result.Message
		}
	}

	return true, "", ""
}

func (kl *Kubelet) canRunPod(pod *v1.Pod) lifecycle.PodAdmitResult {
	attrs := &lifecycle.PodAdmitAttributes{Pod: pod}
	// Get "OtherPods". Rejected pods are failed, so only include admitted pods that are alive.
	attrs.OtherPods = kl.GetActivePods()

	for _, handler := range kl.softAdmitHandlers {
		if result := handler.Admit(attrs); !result.Admit {
			return result
		}
	}

	return lifecycle.PodAdmitResult{Admit: true}
}

// syncLoop is the main loop for processing changes. It watches for changes from
// three channels (file, apiserver, and http) and creates a union of them. For
// any new change seen, will run a sync against desired state and running state. If
// no changes are seen to the configuration, will synchronize the last known desired
// state every sync-frequency seconds. Never returns.
func (kl *Kubelet) syncLoop(ctx context.Context, updates <-chan kubetypes.PodUpdate, handler SyncHandler) {
	klog.InfoS("Starting kubelet main sync loop")
	// The syncTicker wakes up kubelet to checks if there are any pod workers
	// that need to be sync'd. A one-second period is sufficient because the
	// sync interval is defaulted to 10s.
	syncTicker := time.NewTicker(time.Second)
	defer syncTicker.Stop()
	housekeepingTicker := time.NewTicker(housekeepingPeriod)
	defer housekeepingTicker.Stop()
	plegCh := kl.pleg.Watch()
	const (
		base   = 100 * time.Millisecond
		max    = 5 * time.Second
		factor = 2
	)
	duration := base
	// Responsible for checking limits in resolv.conf
	// The limits do not have anything to do with individual pods
	// Since this is called in syncLoop, we don't need to call it anywhere else
	if kl.dnsConfigurer != nil && kl.dnsConfigurer.ResolverConfig != "" {
		kl.dnsConfigurer.CheckLimitsForResolvConf()
	}

	for {
		if err := kl.runtimeState.runtimeErrors(); err != nil {
			klog.ErrorS(err, "Skipping pod synchronization")
			// exponential backoff
			time.Sleep(duration)
			duration = time.Duration(math.Min(float64(max), factor*float64(duration)))
			continue
		}
		// reset backoff if we have a success
		duration = base

		kl.syncLoopMonitor.Store(kl.clock.Now())
		if !kl.syncLoopIteration(ctx, updates, handler, syncTicker.C, housekeepingTicker.C, plegCh) {
			break
		}
		kl.syncLoopMonitor.Store(kl.clock.Now())
	}
}

// syncLoopIteration reads from various channels and dispatches pods to the
// given handler.
//
// Arguments:
// 1.  configCh:       a channel to read config events from
// 2.  handler:        the SyncHandler to dispatch pods to
// 3.  syncCh:         a channel to read periodic sync events from
// 4.  housekeepingCh: a channel to read housekeeping events from
// 5.  plegCh:         a channel to read PLEG updates from
//
// Events are also read from the kubelet liveness manager's update channel.
//
// The workflow is to read from one of the channels, handle that event, and
// update the timestamp in the sync loop monitor.
//
// Here is an appropriate place to note that despite the syntactical
// similarity to the switch statement, the case statements in a select are
// evaluated in a pseudorandom order if there are multiple channels ready to
// read from when the select is evaluated.  In other words, case statements
// are evaluated in random order, and you can not assume that the case
// statements evaluate in order if multiple channels have events.
//
// With that in mind, in truly no particular order, the different channels
// are handled as follows:
//
//   - configCh: dispatch the pods for the config change to the appropriate
//     handler callback for the event type
//   - plegCh: update the runtime cache; sync pod
//   - syncCh: sync all pods waiting for sync
//   - housekeepingCh: trigger cleanup of pods
//   - health manager: sync pods that have failed or in which one or more
//     containers have failed health checks
func (kl *Kubelet) syncLoopIteration(ctx context.Context, configCh <-chan kubetypes.PodUpdate, handler SyncHandler,
	syncCh <-chan time.Time, housekeepingCh <-chan time.Time, plegCh <-chan *pleg.PodLifecycleEvent) bool {
	select {
	case u, open := <-configCh:
		// Update from a config source; dispatch it to the right handler
		// callback.
		if !open {
			klog.ErrorS(nil, "Update channel is closed, exiting the sync loop")
			return false
		}

		switch u.Op {
		case kubetypes.ADD:
			klog.V(2).InfoS("SyncLoop ADD", "source", u.Source, "pods", klog.KObjSlice(u.Pods))
			// After restarting, kubelet will get all existing pods through
			// ADD as if they are new pods. These pods will then go through the
			// admission process and *may* be rejected. This can be resolved
			// once we have checkpointing.
			handler.HandlePodAdditions(u.Pods)
		case kubetypes.UPDATE:
			klog.V(2).InfoS("SyncLoop UPDATE", "source", u.Source, "pods", klog.KObjSlice(u.Pods))
			handler.HandlePodUpdates(u.Pods)
		case kubetypes.REMOVE:
			klog.V(2).InfoS("SyncLoop REMOVE", "source", u.Source, "pods", klog.KObjSlice(u.Pods))
			handler.HandlePodRemoves(u.Pods)
		case kubetypes.RECONCILE:
			klog.V(4).InfoS("SyncLoop RECONCILE", "source", u.Source, "pods", klog.KObjSlice(u.Pods))
			handler.HandlePodReconcile(u.Pods)
		case kubetypes.DELETE:
			klog.V(2).InfoS("SyncLoop DELETE", "source", u.Source, "pods", klog.KObjSlice(u.Pods))
			// DELETE is treated as a UPDATE because of graceful deletion.
			handler.HandlePodUpdates(u.Pods)
		case kubetypes.SET:
			// TODO: Do we want to support this?
			klog.ErrorS(nil, "Kubelet does not support snapshot update")
		default:
			klog.ErrorS(nil, "Invalid operation type received", "operation", u.Op)
		}

		kl.sourcesReady.AddSource(u.Source)

	case e := <-plegCh:
		if isSyncPodWorthy(e) {
			// PLEG event for a pod; sync it.
			if pod, ok := kl.podManager.GetPodByUID(e.ID); ok {
				klog.V(2).InfoS("SyncLoop (PLEG): event for pod", "pod", klog.KObj(pod), "event", e)
				handler.HandlePodSyncs([]*v1.Pod{pod})
			} else {
				// If the pod no longer exists, ignore the event.
				klog.V(4).InfoS("SyncLoop (PLEG): pod does not exist, ignore irrelevant event", "event", e)
			}
		}

		if e.Type == pleg.ContainerDied {
			if containerID, ok := e.Data.(string); ok {
				kl.cleanUpContainersInPod(e.ID, containerID)
			}
		}
	case <-syncCh:
		// Sync pods waiting for sync
		podsToSync := kl.getPodsToSync()
		if len(podsToSync) == 0 {
			break
		}
		klog.V(4).InfoS("SyncLoop (SYNC) pods", "total", len(podsToSync), "pods", klog.KObjSlice(podsToSync))
		handler.HandlePodSyncs(podsToSync)
	case update := <-kl.livenessManager.Updates():
		if update.Result == proberesults.Failure {
			handleProbeSync(kl, update, handler, "liveness", "unhealthy")
		}
	case update := <-kl.readinessManager.Updates():
		ready := update.Result == proberesults.Success
		kl.statusManager.SetContainerReadiness(update.PodUID, update.ContainerID, ready)

		status := ""
		if ready {
			status = "ready"
		}
		handleProbeSync(kl, update, handler, "readiness", status)
	case update := <-kl.startupManager.Updates():
		started := update.Result == proberesults.Success
		kl.statusManager.SetContainerStartup(update.PodUID, update.ContainerID, started)

		status := "unhealthy"
		if started {
			status = "started"
		}
		handleProbeSync(kl, update, handler, "startup", status)
	case <-housekeepingCh:
		if !kl.sourcesReady.AllReady() {
			// If the sources aren't ready or volume manager has not yet synced the states,
			// skip housekeeping, as we may accidentally delete pods from unready sources.
			klog.V(4).InfoS("SyncLoop (housekeeping, skipped): sources aren't ready yet")
		} else {
			start := time.Now()
			klog.V(4).InfoS("SyncLoop (housekeeping)")
			if err := handler.HandlePodCleanups(ctx); err != nil {
				klog.ErrorS(err, "Failed cleaning pods")
			}
			duration := time.Since(start)
			if duration > housekeepingWarningDuration {
				klog.ErrorS(fmt.Errorf("housekeeping took too long"), "Housekeeping took longer than 15s", "seconds", duration.Seconds())
			}
			klog.V(4).InfoS("SyncLoop (housekeeping) end")
		}
	}
	return true
}

func handleProbeSync(kl *Kubelet, update proberesults.Update, handler SyncHandler, probe, status string) {
	// We should not use the pod from manager, because it is never updated after initialization.
	pod, ok := kl.podManager.GetPodByUID(update.PodUID)
	if !ok {
		// If the pod no longer exists, ignore the update.
		klog.V(4).InfoS("SyncLoop (probe): ignore irrelevant update", "probe", probe, "status", status, "update", update)
		return
	}
	klog.V(1).InfoS("SyncLoop (probe)", "probe", probe, "status", status, "pod", klog.KObj(pod))
	handler.HandlePodSyncs([]*v1.Pod{pod})
}

// dispatchWork starts the asynchronous sync of the pod in a pod worker.
// If the pod has completed termination, dispatchWork will perform no action.
func (kl *Kubelet) dispatchWork(pod *v1.Pod, syncType kubetypes.SyncPodType, mirrorPod *v1.Pod, start time.Time) {
	// Run the sync in an async worker.
	kl.podWorkers.UpdatePod(UpdatePodOptions{
		Pod:        pod,
		MirrorPod:  mirrorPod,
		UpdateType: syncType,
		StartTime:  start,
	})
	// Note the number of containers for new pods.
	if syncType == kubetypes.SyncPodCreate {
		metrics.ContainersPerPodCount.Observe(float64(len(pod.Spec.Containers)))
	}
}

// TODO: handle mirror pods in a separate component (issue #17251)
func (kl *Kubelet) handleMirrorPod(mirrorPod *v1.Pod, start time.Time) {
	// Mirror pod ADD/UPDATE/DELETE operations are considered an UPDATE to the
	// corresponding static pod. Send update to the pod worker if the static
	// pod exists.
	if pod, ok := kl.podManager.GetPodByMirrorPod(mirrorPod); ok {
		kl.dispatchWork(pod, kubetypes.SyncPodUpdate, mirrorPod, start)
	}
}

// HandlePodAdditions is the callback in SyncHandler for pods being added from
// a config source.
func (kl *Kubelet) HandlePodAdditions(pods []*v1.Pod) {
	start := kl.clock.Now()
	sort.Sort(sliceutils.PodsByCreationTime(pods))
	for _, pod := range pods {
		existingPods := kl.podManager.GetPods()
		// Always add the pod to the pod manager. Kubelet relies on the pod
		// manager as the source of truth for the desired state. If a pod does
		// not exist in the pod manager, it means that it has been deleted in
		// the apiserver and no action (other than cleanup) is required.
		kl.podManager.AddPod(pod)

		if kubetypes.IsMirrorPod(pod) {
			kl.handleMirrorPod(pod, start)
			continue
		}

		// Only go through the admission process if the pod is not requested
		// for termination by another part of the kubelet. If the pod is already
		// using resources (previously admitted), the pod worker is going to be
		// shutting it down. If the pod hasn't started yet, we know that when
		// the pod worker is invoked it will also avoid setting up the pod, so
		// we simply avoid doing any work.
		if !kl.podWorkers.IsPodTerminationRequested(pod.UID) {
			// We failed pods that we rejected, so activePods include all admitted
			// pods that are alive.
			activePods := kl.filterOutInactivePods(existingPods)

			// Check if we can admit the pod; if not, reject it.
			if ok, reason, message := kl.canAdmitPod(activePods, pod); !ok {
				kl.rejectPod(pod, reason, message)
				continue
			}
		}
		mirrorPod, _ := kl.podManager.GetMirrorPodByPod(pod)
		kl.dispatchWork(pod, kubetypes.SyncPodCreate, mirrorPod, start)
	}
}

// HandlePodUpdates is the callback in the SyncHandler interface for pods
// being updated from a config source.
func (kl *Kubelet) HandlePodUpdates(pods []*v1.Pod) {
	start := kl.clock.Now()
	for _, pod := range pods {
		kl.podManager.UpdatePod(pod)
		if kubetypes.IsMirrorPod(pod) {
			kl.handleMirrorPod(pod, start)
			continue
		}
		mirrorPod, _ := kl.podManager.GetMirrorPodByPod(pod)
		kl.dispatchWork(pod, kubetypes.SyncPodUpdate, mirrorPod, start)
	}
}

// HandlePodRemoves is the callback in the SyncHandler interface for pods
// being removed from a config source.
func (kl *Kubelet) HandlePodRemoves(pods []*v1.Pod) {
	start := kl.clock.Now()
	for _, pod := range pods {
		kl.podManager.DeletePod(pod)
		if kubetypes.IsMirrorPod(pod) {
			kl.handleMirrorPod(pod, start)
			continue
		}
		// Deletion is allowed to fail because the periodic cleanup routine
		// will trigger deletion again.
		if err := kl.deletePod(pod); err != nil {
			klog.V(2).InfoS("Failed to delete pod", "pod", klog.KObj(pod), "err", err)
		}
	}
}

// HandlePodReconcile is the callback in the SyncHandler interface for pods
// that should be reconciled.
func (kl *Kubelet) HandlePodReconcile(pods []*v1.Pod) {
	start := kl.clock.Now()
	for _, pod := range pods {
		// Update the pod in pod manager, status manager will do periodically reconcile according
		// to the pod manager.
		kl.podManager.UpdatePod(pod)

		// Reconcile Pod "Ready" condition if necessary. Trigger sync pod for reconciliation.
		if status.NeedToReconcilePodReadiness(pod) {
			mirrorPod, _ := kl.podManager.GetMirrorPodByPod(pod)
			kl.dispatchWork(pod, kubetypes.SyncPodSync, mirrorPod, start)
		}

		// After an evicted pod is synced, all dead containers in the pod can be removed.
		if eviction.PodIsEvicted(pod.Status) {
			if podStatus, err := kl.podCache.Get(pod.UID); err == nil {
				kl.containerDeletor.deleteContainersInPod("", podStatus, true)
			}
		}
	}
}

// HandlePodSyncs is the callback in the syncHandler interface for pods
// that should be dispatched to pod workers for sync.
func (kl *Kubelet) HandlePodSyncs(pods []*v1.Pod) {
	start := kl.clock.Now()
	for _, pod := range pods {
		mirrorPod, _ := kl.podManager.GetMirrorPodByPod(pod)
		kl.dispatchWork(pod, kubetypes.SyncPodSync, mirrorPod, start)
	}
}

// LatestLoopEntryTime returns the last time in the sync loop monitor.
func (kl *Kubelet) LatestLoopEntryTime() time.Time {
	val := kl.syncLoopMonitor.Load()
	if val == nil {
		return time.Time{}
	}
	return val.(time.Time)
}

// updateRuntimeUp calls the container runtime status callback, initializing
// the runtime dependent modules when the container runtime first comes up,
// and returns an error if the status check fails.  If the status check is OK,
// update the container runtime uptime in the kubelet runtimeState.
func (kl *Kubelet) updateRuntimeUp() {
	kl.updateRuntimeMux.Lock()
	defer kl.updateRuntimeMux.Unlock()
	ctx := context.Background()

	s, err := kl.containerRuntime.Status(ctx)
	if err != nil {
		klog.ErrorS(err, "Container runtime sanity check failed")
		return
	}
	if s == nil {
		klog.ErrorS(nil, "Container runtime status is nil")
		return
	}
	// Periodically log the whole runtime status for debugging.
	klog.V(4).InfoS("Container runtime status", "status", s)
	klogErrorS := klog.ErrorS
	if !kl.containerRuntimeReadyExpected {
		klogErrorS = klog.V(4).ErrorS
	}
	networkReady := s.GetRuntimeCondition(kubecontainer.NetworkReady)
	if networkReady == nil || !networkReady.Status {
		klogErrorS(nil, "Container runtime network not ready", "networkReady", networkReady)
		kl.runtimeState.setNetworkState(fmt.Errorf("container runtime network not ready: %v", networkReady))
	} else {
		// Set nil if the container runtime network is ready.
		kl.runtimeState.setNetworkState(nil)
	}
	// information in RuntimeReady condition will be propagated to NodeReady condition.
	runtimeReady := s.GetRuntimeCondition(kubecontainer.RuntimeReady)
	// If RuntimeReady is not set or is false, report an error.
	if runtimeReady == nil || !runtimeReady.Status {
		klogErrorS(nil, "Container runtime not ready", "runtimeReady", runtimeReady)
		kl.runtimeState.setRuntimeState(fmt.Errorf("container runtime not ready: %v", runtimeReady))
		return
	}
	kl.runtimeState.setRuntimeState(nil)
	kl.oneTimeInitializer.Do(kl.initializeRuntimeDependentModules)
	kl.runtimeState.setRuntimeSync(kl.clock.Now())
}

// GetConfiguration returns the KubeletConfiguration used to configure the kubelet.
func (kl *Kubelet) GetConfiguration() kubeletconfiginternal.KubeletConfiguration {
	return kl.kubeletConfiguration
}

// BirthCry sends an event that the kubelet has started up.
func (kl *Kubelet) BirthCry() {
	// Make an event that kubelet restarted.
	kl.recorder.Eventf(kl.nodeRef, v1.EventTypeNormal, events.StartingKubelet, "Starting kubelet.")
}

// ResyncInterval returns the interval used for periodic syncs.
func (kl *Kubelet) ResyncInterval() time.Duration {
	return kl.resyncInterval
}

// ListenAndServe runs the kubelet HTTP server.
func (kl *Kubelet) ListenAndServe(kubeCfg *kubeletconfiginternal.KubeletConfiguration, tlsOptions *server.TLSOptions,
	auth server.AuthInterface, tp trace.TracerProvider) {
	server.ListenAndServeKubeletServer(kl, kl.resourceAnalyzer, kubeCfg, tlsOptions, auth, tp)
}

// ListenAndServeReadOnly runs the kubelet HTTP server in read-only mode.
func (kl *Kubelet) ListenAndServeReadOnly(address net.IP, port uint) {
	server.ListenAndServeKubeletReadOnlyServer(kl, kl.resourceAnalyzer, address, port)
}

// ListenAndServePodResources runs the kubelet podresources grpc service
func (kl *Kubelet) ListenAndServePodResources() {
	socket, err := util.LocalEndpoint(kl.getPodResourcesDir(), podresources.Socket)
	if err != nil {
		klog.V(2).InfoS("Failed to get local endpoint for PodResources endpoint", "err", err)
		return
	}
	server.ListenAndServePodResources(socket, kl.podManager, kl.containerManager, kl.containerManager, kl.containerManager)
}

// Delete the eligible dead container instances in a pod. Depending on the configuration, the latest dead containers may be kept around.
func (kl *Kubelet) cleanUpContainersInPod(podID types.UID, exitedContainerID string) {
	if podStatus, err := kl.podCache.Get(podID); err == nil {
		// When an evicted or deleted pod has already synced, all containers can be removed.
		removeAll := kl.podWorkers.ShouldPodContentBeRemoved(podID)
		kl.containerDeletor.deleteContainersInPod(exitedContainerID, podStatus, removeAll)
	}
}

// fastStatusUpdateOnce starts a loop that checks if the current state of kubelet + container runtime
// would be able to turn the node ready, and sync the ready state to the apiserver as soon as possible.
// Function returns after the node status update after such event, or when the node is already ready.
// Function is executed only during Kubelet start which improves latency to ready node by updating
// kubelet state, runtime status and node statuses ASAP.
func (kl *Kubelet) fastStatusUpdateOnce() {
	ctx := context.Background()
	start := kl.clock.Now()
	stopCh := make(chan struct{})

	// Keep trying to make fast node status update until either timeout is reached or an update is successful.
	wait.Until(func() {
		// fastNodeStatusUpdate returns true when it succeeds or when the grace period has expired
		// (status was not updated within nodeReadyGracePeriod and the second argument below gets true),
		// then we close the channel and abort the loop.
		if kl.fastNodeStatusUpdate(ctx, kl.clock.Since(start) >= nodeReadyGracePeriod) {
			close(stopCh)
		}
	}, 100*time.Millisecond, stopCh)
}

// CheckpointContainer tries to checkpoint a container. The parameters are used to
// look up the specified container. If the container specified by the given parameters
// cannot be found an error is returned. If the container is found the container
// engine will be asked to checkpoint the given container into the kubelet's default
// checkpoint directory.
func (kl *Kubelet) CheckpointContainer(
	ctx context.Context,
	podUID types.UID,
	podFullName,
	containerName string,
	options *runtimeapi.CheckpointContainerRequest,
) error {
	container, err := kl.findContainer(ctx, podFullName, podUID, containerName)
	if err != nil {
		return err
	}
	if container == nil {
		return fmt.Errorf("container %v not found", containerName)
	}

	options.Location = filepath.Join(
		kl.getCheckpointsDir(),
		fmt.Sprintf(
			"checkpoint-%s-%s-%s.tar",
			podFullName,
			containerName,
			time.Now().Format(time.RFC3339),
		),
	)

	options.ContainerId = string(container.ID.ID)

	if err := kl.containerRuntime.CheckpointContainer(ctx, options); err != nil {
		return err
	}

	return nil
}

// ListMetricDescriptors gets the descriptors for the metrics that will be returned in ListPodSandboxMetrics.
func (kl *Kubelet) ListMetricDescriptors(ctx context.Context) ([]*runtimeapi.MetricDescriptor, error) {
	return kl.containerRuntime.ListMetricDescriptors(ctx)
}

// ListPodSandboxMetrics retrieves the metrics for all pod sandboxes.
func (kl *Kubelet) ListPodSandboxMetrics(ctx context.Context) ([]*runtimeapi.PodSandboxMetrics, error) {
	return kl.containerRuntime.ListPodSandboxMetrics(ctx)
}

func (kl *Kubelet) supportLocalStorageCapacityIsolation() bool {
	return kl.GetConfiguration().LocalStorageCapacityIsolation
}

// isSyncPodWorthy filters out events that are not worthy of pod syncing
func isSyncPodWorthy(event *pleg.PodLifecycleEvent) bool {
	// ContainerRemoved doesn't affect pod state
	return event.Type != pleg.ContainerRemoved
}