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startKubelet

kubelet源码分析(三)之 startKubelet

以下代码分析基于 kubernetes v1.12.0 版本。
本文主要分析startKubelet,其中主要是kubelet.Run部分,该部分的内容主要是初始化并运行一些manager。对于kubelet所包含的各种manager的执行逻辑和pod的生命周期管理逻辑待后续文章分析。
后续的文章主要会分类分析pkg/kubelet部分的代码实现。
kubeletpkg代码目录结构:
kubelet
├── apis # 定义一些相关接口
├── cadvisor # cadvisor
├── cm # ContainerManager、cpu manger、cgroup manager
├── config
├── configmap # configmap manager
├── container # Runtime、ImageService
├── dockershim # docker的相关调用
├── eviction # eviction manager
├── images # image manager
├── kubeletconfig
├── kuberuntime # 核心:kubeGenericRuntimeManager、runtime容器的相关操作
├── lifecycle
├── mountpod
├── network # pod dns
├── nodelease
├── nodestatus # MachineInfo、节点相关信息
├── pleg # PodLifecycleEventGenerator
├── pod # 核心:pod manager、mirror pod
├── preemption
├── qos # 资源服务质量,不过暂时内容很少
├── remote # RemoteRuntimeService
├── server
├── stats # StatsProvider
├── status # status manager
├── types # PodUpdate、PodOperation
├── volumemanager # VolumeManager
├── kubelet.go # 核心: SyncHandler、kubelet的大部分操作
├── kubelet_getters.go # 各种get操作,例如获取相关目录:getRootDir、getPodsDir、getPluginsDir
├── kubelet_network.go #
├── kubelet_network_linux.go
├── kubelet_node_status.go # registerWithAPIServer、initialNode、syncNodeStatus
├── kubelet_pods.go # 核心:pod的增删改查等相关操作、podKiller、
├── kubelet_resources.go
├── kubelet_volumes.go # ListVolumesForPod、cleanupOrphanedPodDirs
├── oom_watcher.go # OOMWatcher
├── pod_container_deletor.go
├── pod_workers.go # 核心:PodWorkers、UpdatePodOptions、syncPodOptions、managePodLoop
├── runonce.go # RunOnce
├── runtime.go
...
startKubelet的函数位于cmd/kubelet/app/server.go,启动并运行一个kubelet,运行kubelet的逻辑代码位于pkg/kubelet/kubelet.go
主要内容如下:
  1. 1.
    运行一个kubelet,执行kubelet中各种manager的相关逻辑。
  2. 2.
    运行kubelet server启动监听服务。
此部分代码位于cmd/kubelet/app/server.go
func startKubelet(k kubelet.Bootstrap, podCfg *config.PodConfig, kubeCfg *kubeletconfiginternal.KubeletConfiguration, kubeDeps *kubelet.Dependencies, enableServer bool) {
// start the kubelet
go wait.Until(func() {
k.Run(podCfg.Updates())
}, 0, wait.NeverStop)
// start the kubelet server
if enableServer {
go k.ListenAndServe(net.ParseIP(kubeCfg.Address), uint(kubeCfg.Port), kubeDeps.TLSOptions, kubeDeps.Auth, kubeCfg.EnableDebuggingHandlers, kubeCfg.EnableContentionProfiling)
}
if kubeCfg.ReadOnlyPort > 0 {
go k.ListenAndServeReadOnly(net.ParseIP(kubeCfg.Address), uint(kubeCfg.ReadOnlyPort))
}
}
Kubelet.Run方法主要将NewMainKubelet构造的各种manager运行起来,让各种manager执行相应的功能,大部分manager为常驻进程的方式运行。
Kubelet.Run完整代码如下:
此部分代码位于pkg/kubelet/kubelet.go
// Run starts the kubelet reacting to config updates
func (kl *Kubelet) Run(updates <-chan kubetypes.PodUpdate) {
if kl.logServer == nil {
kl.logServer = http.StripPrefix("/logs/", http.FileServer(http.Dir("/var/log/")))
}
if kl.kubeClient == nil {
glog.Warning("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())
glog.Fatal(err)
}
// Start volume manager
go kl.volumeManager.Run(kl.sourcesReady, wait.NeverStop)
if kl.kubeClient != nil {
// Start syncing node status immediately, this may set up things the runtime needs to run.
go wait.Until(kl.syncNodeStatus, kl.nodeStatusUpdateFrequency, wait.NeverStop)
go kl.fastStatusUpdateOnce()
// start syncing lease
if utilfeature.DefaultFeatureGate.Enabled(features.NodeLease) {
go kl.nodeLeaseController.Run(wait.NeverStop)
}
}
go wait.Until(kl.updateRuntimeUp, 5*time.Second, wait.NeverStop)
// Start loop to sync iptables util rules
if kl.makeIPTablesUtilChains {
go wait.Until(kl.syncNetworkUtil, 1*time.Minute, wait.NeverStop)
}
// Start a goroutine responsible for killing pods (that are not properly
// handled by pod workers).
go wait.Until(kl.podKiller, 1*time.Second, wait.NeverStop)
// Start component sync loops.
kl.statusManager.Start()
kl.probeManager.Start()
// Start syncing RuntimeClasses if enabled.
if kl.runtimeClassManager != nil {
go kl.runtimeClassManager.Run(wait.NeverStop)
}
// Start the pod lifecycle event generator.
kl.pleg.Start()
kl.syncLoop(updates, kl)
}
以下对Kubelet.Run分段进行分析。

3. initializeModules

initializeModules包含了imageManagerserverCertificateManageroomWatcherresourceAnalyzer
主要流程如下:
  1. 1.
    创建文件系统目录,包括kubelet的root目录、pods的目录、plugins的目录和容器日志目录。
  2. 2.
    启动imageManager、serverCertificateManager、oomWatcher、resourceAnalyzer。
各种manager的说明如下:
  • imageManager:负责镜像垃圾回收。
  • serverCertificateManager:负责处理证书。
  • oomWatcher:监控内存使用,是否发生内存耗尽。
  • resourceAnalyzer:监控资源使用情况。
完整代码如下:
此部分代码位于pkg/kubelet/kubelet.go
// 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(kl.runtimeCache, collectors.NewVolumeStatsCollector(kl))
// 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 {
glog.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 err := kl.oomWatcher.Start(kl.nodeRef); err != nil {
return fmt.Errorf("Failed to start OOM watcher %v", err)
}
// Start resource analyzer
kl.resourceAnalyzer.Start()
return nil
}

3.1. setupDataDirs

initializeModules先创建相关目录。
具体目录如下:
  • ContainerLogsDir:目录为/var/log/containers。
  • rootDirectory:由参数传入,一般为/var/lib/kubelet
  • PodsDir:目录为{rootDirectory}/pods。
  • PluginsDir:目录为{rootDirectory}/plugins。
initializeModules中setupDataDirs的相关代码如下:
// 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 {
glog.Errorf("Failed to create directory %q: %v", ContainerLogsDir, err)
}
}
setupDataDirs代码如下
// setupDataDirs creates:
// 1. the root directory
// 2. the pods directory
// 3. the plugins directory
func (kl *Kubelet) setupDataDirs() error {
kl.rootDirectory = path.Clean(kl.rootDirectory)
if err := os.MkdirAll(kl.getRootDir(), 0750); err != nil {
return fmt.Errorf("error creating root directory: %v", err)
}
if err := kl.mounter.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)
}
return nil
}

3.2. manager

initializeModules中的manager如下:
// 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 err := kl.oomWatcher.Start(kl.nodeRef); err != nil {
return fmt.Errorf("Failed to start OOM watcher %v", err)
}
// Start resource analyzer
kl.resourceAnalyzer.Start()

4. 运行各种manager

4.1. volumeManager

volumeManager主要运行一组异步循环,根据在此节点上安排的pod调整哪些volume需要attached/detached/mounted/unmounted
// Start volume manager
go kl.volumeManager.Run(kl.sourcesReady, wait.NeverStop)
volumeManager.Run实现代码如下:
func (vm *volumeManager) Run(sourcesReady config.SourcesReady, stopCh <-chan struct{}) {
defer runtime.HandleCrash()
go vm.desiredStateOfWorldPopulator.Run(sourcesReady, stopCh)
glog.V(2).Infof("The desired_state_of_world populator starts")
glog.Infof("Starting Kubelet Volume Manager")
go vm.reconciler.Run(stopCh)
metrics.Register(vm.actualStateOfWorld, vm.desiredStateOfWorld, vm.volumePluginMgr)
<-stopCh
glog.Infof("Shutting down Kubelet Volume Manager")
}

4.2. syncNodeStatus

syncNodeStatus通过goroutine的方式定期执行,它将节点的状态同步给master,必要的时候注册kubelet。
if kl.kubeClient != nil {
// Start syncing node status immediately, this may set up things the runtime needs to run.
go wait.Until(kl.syncNodeStatus, kl.nodeStatusUpdateFrequency, wait.NeverStop)
go kl.fastStatusUpdateOnce()
// start syncing lease
if utilfeature.DefaultFeatureGate.Enabled(features.NodeLease) {
go kl.nodeLeaseController.Run(wait.NeverStop)
}
}

4.3. updateRuntimeUp

updateRuntimeUp调用容器运行时状态回调,在容器运行时首次启动时初始化运行时相关模块,如果状态检查失败则返回错误。 如果状态检查正常,在kubelet runtimeState中更新容器运行时的正常运行时间。
go wait.Until(kl.updateRuntimeUp, 5*time.Second, wait.NeverStop)

4.4. syncNetworkUtil

通过循环的方式同步iptables的规则,不过当前代码并没有执行任何操作。
// Start loop to sync iptables util rules
if kl.makeIPTablesUtilChains {
go wait.Until(kl.syncNetworkUtil, 1*time.Minute, wait.NeverStop)
}

4.5. podKiller

但pod没有被podworker正确处理的时候,启动一个goroutine负责杀死pod。
// Start a goroutine responsible for killing pods (that are not properly
// handled by pod workers).
go wait.Until(kl.podKiller, 1*time.Second, wait.NeverStop)
podKiller代码如下:
此部分代码位于pkg/kubelet/kubelet_pods.go
// podKiller launches a goroutine to kill a pod received from the channel if
// another goroutine isn't already in action.
func (kl *Kubelet) podKiller() {
killing := sets.NewString()
// guard for the killing set
lock := sync.Mutex{}
for podPair := range kl.podKillingCh {
runningPod := podPair.RunningPod
apiPod := podPair.APIPod
lock.Lock()
exists := killing.Has(string(runningPod.ID))
if !exists {
killing.Insert(string(runningPod.ID))
}
lock.Unlock()
if !exists {
go func(apiPod *v1.Pod, runningPod *kubecontainer.Pod) {
glog.V(2).Infof("Killing unwanted pod %q", runningPod.Name)
err := kl.killPod(apiPod, runningPod, nil, nil)
if err != nil {
glog.Errorf("Failed killing the pod %q: %v", runningPod.Name, err)
}
lock.Lock()
killing.Delete(string(runningPod.ID))
lock.Unlock()
}(apiPod, runningPod)
}
}
}

4.6. statusManager

使用apiserver同步pods状态; 也用作状态缓存。
// Start component sync loops.
kl.statusManager.Start()
statusManager.Start的实现代码如下:
func (m *manager) Start() {
// Don't start the status manager if we don't have a client. This will happen
// on the master, where the kubelet is responsible for bootstrapping the pods
// of the master components.
if m.kubeClient == nil {
glog.Infof("Kubernetes client is nil, not starting status manager.")
return
}
glog.Info("Starting to sync pod status with apiserver")
syncTicker := time.Tick(syncPeriod)
// syncPod and syncBatch share the same go routine to avoid sync races.
go wait.Forever(func() {
select {
case syncRequest := <-m.podStatusChannel:
glog.V(5).Infof("Status Manager: syncing pod: %q, with status: (%d, %v) from podStatusChannel",
syncRequest.podUID, syncRequest.status.version, syncRequest.status.status)
m.syncPod(syncRequest.podUID, syncRequest.status)
case <-syncTicker:
m.syncBatch()
}
}, 0)
}

4.7. probeManager

处理容器探针
kl.probeManager.Start()

4.8. runtimeClassManager

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

4.9. PodLifecycleEventGenerator

// Start the pod lifecycle event generator.
kl.pleg.Start()
PodLifecycleEventGenerator是一个pod生命周期时间生成器接口,具体如下:
// PodLifecycleEventGenerator contains functions for generating pod life cycle events.
type PodLifecycleEventGenerator interface {
Start()
Watch() chan *PodLifecycleEvent
Healthy() (bool, error)
}
start方法具体实现如下:
// Start spawns a goroutine to relist periodically.
func (g *GenericPLEG) Start() {
go wait.Until(g.relist, g.relistPeriod, wait.NeverStop)
}

4.10. syncLoop

最后调用syncLoop来执行同步变化变更的循环。
kl.syncLoop(updates, kl)

5. syncLoop

syncLoop是处理变化的循环。 它监听来自三种channel(file,apiserver和http)的更改。 对于看到的任何新更改,将针对所需状态和运行状态运行同步。 如果没有看到配置的变化,将在每个同步频率秒同步最后已知的所需状态。
// 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(updates <-chan kubetypes.PodUpdate, handler SyncHandler) {
glog.Info("Starting kubelet main sync loop.")
// The resyncTicker 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
for {
if rs := kl.runtimeState.runtimeErrors(); len(rs) != 0 {
glog.Infof("skipping pod synchronization - %v", rs)
// 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(updates, handler, syncTicker.C, housekeepingTicker.C, plegCh) {
break
}
kl.syncLoopMonitor.Store(kl.clock.Now())
}
}
其中调用了syncLoopIteration的函数来执行更具体的监控pod变化的循环。syncLoopIteration代码逻辑待后续单独分析。

6. 总结

6.1. 基本流程

Kubelet.Run主要流程如下:
  1. 1.
    初始化模块,其实就是运行imageManagerserverCertificateManageroomWatcherresourceAnalyzer
  2. 2.
    运行各种manager,大部分以常驻goroutine的方式运行,其中包括volumeManagerstatusManager等。
  3. 3.
    执行处理变更的循环函数syncLoop,对pod的生命周期进行管理。
syncLoop:
syncLoop函数,对pod的生命周期进行管理,其中syncLoop调用了syncLoopIteration函数,该函数根据podUpdate的信息,针对不同的操作,由SyncHandler来执行pod的增删改查等生命周期的管理,其中的syncHandler包括HandlePodSyncsHandlePodCleanups等。该部分逻辑待后续文章具体分析。

6.2. Manager

以下介绍kubelet运行时涉及到的manager的内容。
manager
说明
imageManager
负责镜像垃圾回收
serverCertificateManager
负责处理证书
oomWatcher
监控内存使用,是否发生内存耗尽即OOM
resourceAnalyzer
监控资源使用情况
volumeManager
对pod执行attached/detached/mounted/unmounted操作
statusManager
使用apiserver同步pods状态; 也用作状态缓存
probeManager
处理容器探针
runtimeClassManager
同步RuntimeClasses
podKiller
负责杀死pod
参考文章: