本篇文章给大家分享的是有关如何理解kubernetes数据卷管理的源码，小编觉得挺实用的，因此分享给大家学习，希望大家阅读完这篇文章后可以有所收获，话不多说，跟着小编一起来看看吧。
概述
volume是k8s中很重要的一个环节，主要用来存储k8s中pod生产的一些系统或者业务数据。k8s在kubelet中提供了volume管理的逻辑
源码分析
首先是kubelet启动方法
func main() { s := options.NewKubeletServer() s.AddFlags(pflag.CommandLine) flag.InitFlags() logs.InitLogs() defer logs.FlushLogs() verflag.PrintAndExitIfRequested() if err := app.Run(s, nil); err != nil { fmt.Fprintf(os.Stderr, "error: %v\n", err) os.Exit(1) }}很容易发现run方法中包含了kubelet所有重要信息
func run(s *options.KubeletServer, kubeDeps *kubelet.KubeletDeps) (err error) { //配置验证 ... if kubeDeps == nil { ... kubeDeps, err = UnsecuredKubeletDeps(s) ... } //初始化cAdvisor以及containerManager等管理器 ... if err := RunKubelet(&s.KubeletConfiguration, kubeDeps, s.RunOnce, standaloneMode); err != nil { return err } ...}里面有两个与volume管理相关的重要方法
UnsecuredKubeletDeps：会初始化docker client、网络管理插件、数据管理插件等系统核心组件，因为不方便对外部开放，所以命名为unsecure。其中我们需要关注的是它对volume plugin的初始化操作
func UnsecuredKubeletDeps(s *options.KubeletServer) (*kubelet.KubeletDeps, error) { ...return &kubelet.KubeletDeps{Auth: nil, CAdvisorInterface: nil, Cloud: nil, ContainerManager: nil,DockerClient: dockerClient,KubeClient: nil,ExternalKubeClient: nil,Mounter: mounter,NetworkPlugins: ProbeNetworkPlugins(s.NetworkPluginDir, s.CNIConfDir, s.CNIBinDir),OOMAdjuster: oom.NewOOMAdjuster(),OSInterface: kubecontainer.RealOS{},Writer: writer,VolumePlugins: ProbeVolumePlugins(s.VolumePluginDir),TLSOptions: tlsOptions,}, nil}在初始化volume plugin的时候会传递VolumePluginDir作为自定义plugin的路径，默认路径为**/usr/libexec/kubernetes/kubelet-plugins/volume/exec/**
func ProbeVolumePlugins(pluginDir string) []volume.VolumePlugin {allPlugins := []volume.VolumePlugin{}allPlugins = append(allPlugins, aws_ebs.ProbeVolumePlugins()...)allPlugins = append(allPlugins, empty_dir.ProbeVolumePlugins()...)allPlugins = append(allPlugins, gce_pd.ProbeVolumePlugins()...)allPlugins = append(allPlugins, git_repo.ProbeVolumePlugins()...)allPlugins = append(allPlugins, host_path.ProbeVolumePlugins(volume.VolumeConfig{})...)allPlugins = append(allPlugins, nfs.ProbeVolumePlugins(volume.VolumeConfig{})...)allPlugins = append(allPlugins, secret.ProbeVolumePlugins()...)allPlugins = append(allPlugins, iscsi.ProbeVolumePlugins()...)allPlugins = append(allPlugins, glusterfs.ProbeVolumePlugins()...)allPlugins = append(allPlugins, rbd.ProbeVolumePlugins()...)allPlugins = append(allPlugins, cinder.ProbeVolumePlugins()...)allPlugins = append(allPlugins, quobyte.ProbeVolumePlugins()...)allPlugins = append(allPlugins, cephfs.ProbeVolumePlugins()...)allPlugins = append(allPlugins, downwardapi.ProbeVolumePlugins()...)allPlugins = append(allPlugins, fc.ProbeVolumePlugins()...)allPlugins = append(allPlugins, flocker.ProbeVolumePlugins()...)allPlugins = append(allPlugins, flexvolume.ProbeVolumePlugins(pluginDir)...)allPlugins = append(allPlugins, azure_file.ProbeVolumePlugins()...)allPlugins = append(allPlugins, configmap.ProbeVolumePlugins()...)allPlugins = append(allPlugins, vsphere_volume.ProbeVolumePlugins()...)allPlugins = append(allPlugins, azure_dd.ProbeVolumePlugins()...)allPlugins = append(allPlugins, photon_pd.ProbeVolumePlugins()...)allPlugins = append(allPlugins, projected.ProbeVolumePlugins()...)allPlugins = append(allPlugins, portworx.ProbeVolumePlugins()...)allPlugins = append(allPlugins, scaleio.ProbeVolumePlugins()...)return allPlugins}可以观察到众多插件中，有一个名为flexvolume，只有这个插件带有参数pluginDir，说明只有这个插件支持自定义实现。具体kubelet怎么和这些插件交互，以及这些插件提供哪些接口，还需要继续阅读代码
RunKubelet：这才是kubelet服务的启动方法，其中最重要的功能都藏在startKubelet中
func RunKubelet(kubeCfg *componentconfig.KubeletConfiguration, kubeDeps *kubelet.KubeletDeps, runOnce bool, standaloneMode bool) error {//初始化启动器...if runOnce {if _, err := k.RunOnce(podCfg.Updates()); err != nil {return fmt.Errorf("runonce failed: %v", err)}glog.Infof("Started kubelet %s as runonce", version.Get().String())} else {startKubelet(k, podCfg, kubeCfg, kubeDeps)glog.Infof("Started kubelet %s", version.Get().String())}return nil}startKubelet包含两个环节
func startKubelet(k kubelet.KubeletBootstrap, podCfg *config.PodConfig, kubeCfg *componentconfig.KubeletConfiguration, kubeDeps *kubelet.KubeletDeps) {// 同步pod信息go wait.Until(func() { k.Run(podCfg.Updates()) }, 0, wait.NeverStop)// 启动kubelet服务if kubeCfg.EnableServer {go wait.Until(func() {k.ListenAndServe(net.ParseIP(kubeCfg.Address), uint(kubeCfg.Port), kubeDeps.TLSOptions, kubeDeps.Auth, kubeCfg.EnableDebuggingHandlers, kubeCfg.EnableContentionProfiling)}, 0, wait.NeverStop)}if kubeCfg.ReadOnlyPort > 0 {go wait.Until(func() {k.ListenAndServeReadOnly(net.ParseIP(kubeCfg.Address), uint(kubeCfg.ReadOnlyPort))}, 0, wait.NeverStop)}}跟踪同步pod信息的Run方法，会追查到这段代码
func (kl *Kubelet) Run(updates <-chan kubetypes.PodUpdate) { ...go kl.volumeManager.Run(kl.sourcesReady, wait.NeverStop)if kl.kubeClient != nil {//同步node信息go wait.Until(kl.syncNodeStatus, kl.nodeStatusUpdateFrequency, wait.NeverStop)}// 同步pod信息kl.pleg.Start()kl.syncLoop(updates, kl)}kl.volumeManager是kubelet进行数据卷管理的核心接口
type VolumeManager interface {Run(sourcesReady config.SourcesReady, stopCh <-chan struct{})WaitForAttachAndMount(pod *v1.Pod) errorGetMountedVolumesForPod(podName types.UniquePodName) container.VolumeMapGetExtraSupplementalGroupsForPod(pod *v1.Pod) []int64GetVolumesInUse() []v1.UniqueVolumeNameReconcilerStatesHasBeenSynced() boolVolumeIsAttached(volumeName v1.UniqueVolumeName) boolMarkVolumesAsReportedInUse(volumesReportedAsInUse []v1.UniqueVolumeName)}VolumeManager的Run会执行一个异步循环，当pod被调度到该node，它会检查该pod所申请的所有volume，根据这些volume与pod的关系做attach/detach/mount/unmount操作
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)<-stopChglog.Infof("Shutting down Kubelet Volume Manager")}其中重点关注的地方是vm.desiredStateOfWorldPopulator.Run和vm.reconciler.Run这两个方法。在介绍这两个方法之前，需要补充一个关键信息，这也是理解这两个方法的关键信息。
kubelet管理volume的方式基于两个不同的状态：
理解了这两个状态，就能大概知道vm.desiredStateOfWorldPopulator.Run这个方法是干什么的呢。很明显，它就是根据从apiserver同步到的pod信息，来更新DesiredStateOfWorld。另外一个方法vm.reconciler.Run，是预期状态和实际状态的协调者，它负责将实际状态调整成与预期状态。预期状态的更新实现，以及协调者具体如何协调，需要继续阅读代码才能理解
追踪vm.desiredStateOfWorldPopulator.Run，我们发现这段逻辑
func (dswp *desiredStateOfWorldPopulator) findAndAddNewPods() {for _, pod := range dswp.podManager.GetPods() {if dswp.isPodTerminated(pod) {continue}dswp.processPodVolumes(pod)}}kubelet会同步新增的pod到desiredStateOfWorldPopulator的podManager中。这段代码就是轮询其中非结束状态的pod，并交给desiredStateOfWorldPopulator处理
func (dswp *desiredStateOfWorldPopulator) processPodVolumes(pod *v1.Pod) {...for _, podVolume := range pod.Spec.Volumes {volumeSpec, volumeGidValue, err :=dswp.createVolumeSpec(podVolume, pod.Namespace)if err != nil {glog.Errorf("Error processing volume %q for pod %q: %v",podVolume.Name,format.Pod(pod),err)continue}_, err = dswp.desiredStateOfWorld.AddPodToVolume(uniquePodName, pod, volumeSpec, podVolume.Name, volumeGidValue)if err != nil {glog.Errorf("Failed to add volume %q (specName: %q) for pod %q to desiredStateOfWorld. err=%v",podVolume.Name,volumeSpec.Name(),uniquePodName,err)}glog.V(10).Infof("Added volume %q (volSpec=%q) for pod %q to desired state.",podVolume.Name,volumeSpec.Name(),uniquePodName)}dswp.markPodProcessed(uniquePodName)}desiredStateOfWorldPopulator并不处理很重的逻辑，只是作为一个代理，将控制某个pod预期状态的逻辑交付给desiredStateOfWorld，并标记为已处理
func (dsw *desiredStateOfWorld) AddPodToVolume(podName types.UniquePodName,pod *v1.Pod,volumeSpec *volume.Spec,outerVolumeSpecName string,volumeGidValue string) (v1.UniqueVolumeName, error) {...dsw.volumesToMount[volumeName].podsToMount[podName] = podToMount{podName: podName,pod: pod,spec: volumeSpec,outerVolumeSpecName: outerVolumeSpecName,}return volumeName, nil}这段逻辑中，我们忽略了前面一系列预处理操作，直接关注最核心的地方：确定预期状态的方式就是，用一个映射表结构，绑定volume到pod之间的关系，这个关系表就是绑定关系的参考依据
看完了desiredStateOfWorldPopulator的处理逻辑，接着进入另一个核心接口reconciler。它才是volume manager中最重要的控制器
追踪reconciler的Run方法，我们定位到最核心的一段代码
func (rc *reconciler) reconcile() {//umountfor _, mountedVolume := range rc.actualStateOfWorld.GetMountedVolumes() {if !rc.desiredStateOfWorld.PodExistsInVolume(mountedVolume.PodName, mountedVolume.VolumeName) {...err := rc.operationExecutor.UnmountVolume(mountedVolume.MountedVolume, rc.actualStateOfWorld)...}}// attach/mountfor _, volumeToMount := range rc.desiredStateOfWorld.GetVolumesToMount() {volMounted, devicePath, err := rc.actualStateOfWorld.PodExistsInVolume(volumeToMount.PodName, volumeToMount.VolumeName)volumeToMount.DevicePath = devicePathif cache.IsVolumeNotAttachedError(err) {...err := rc.operationExecutor.AttachVolume(volumeToAttach, rc.actualStateOfWorld)...} else if !volMounted || cache.IsRemountRequiredError(err) {...err := rc.operationExecutor.MountVolume(rc.waitForAttachTimeout,volumeToMount.VolumeToMount,rc.actualStateOfWorld)...}}//detach/unmountfor _, attachedVolume := range rc.actualStateOfWorld.GetUnmountedVolumes() {if !rc.desiredStateOfWorld.VolumeExists(attachedVolume.VolumeName) &&!rc.operationExecutor.IsOperationPending(attachedVolume.VolumeName, nestedpendingoperations.EmptyUniquePodName) {if attachedVolume.GloballyMounted {...err := rc.operationExecutor.UnmountDevice(attachedVolume.AttachedVolume, rc.actualStateOfWorld, rc.mounter)...} else {...err := rc.operationExecutor.DetachVolume(attachedVolume.AttachedVolume, false,rc.actualStateOfWorld)...}}}}我略去了多余的代码，保留最核心的部分。这段控制逻辑就是一个协调器，具体要做的事情就是，根据实际状态与预期状态的差异，做协调操作
如果采用自定义的flexvolume插件，上述这些方法会对插件中实现的方法进行系统调用
flex volume提供的lvm插件。如果需要支持mount和unmount操作，可以在这个脚本中补充
#!/bin/bash# 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.# Notes:# - Please install "jq" package before using this driver.usage() {err "Invalid usage. Usage: "err "\t$0 init"err "\t$0 attach <json params> <nodename>"err "\t$0 detach <mount device> <nodename>"err "\t$0 waitforattach <mount device> <json params>"err "\t$0 mountdevice <mount dir> <mount device> <json params>"err "\t$0 unmountdevice <mount dir>"err "\t$0 isattached <json params> <nodename>"exit 1}err() {echo -ne $* 1>&2}log() {echo -ne $* >&1}ismounted() {MOUNT=`findmnt -n ${MNTPATH} 2>/dev/null | cut -d' ' -f1`if [ "${MOUNT}" == "${MNTPATH}" ]; thenecho "1"elseecho "0"fi}getdevice() {VOLUMEID=$(echo ${JSON_PARAMS} | jq -r '.volumeID')VG=$(echo ${JSON_PARAMS}|jq -r '.volumegroup')# LVM substitutes - with --VOLUMEID=`echo $VOLUMEID|sed s/-/--/g`VG=`echo $VG|sed s/-/--/g`DMDEV="/dev/mapper/${VG}-${VOLUMEID}"echo ${DMDEV}}attach() {JSON_PARAMS=$1SIZE=$(echo $1 | jq -r '.size')DMDEV=$(getdevice)if [ ! -b "${DMDEV}" ]; thenerr "{\"status\": \"Failure\", \"message\": \"Volume ${VOLUMEID} does not exist\"}"exit 1filog "{\"status\": \"Success\", \"device\":\"${DMDEV}\"}"exit 0}detach() {log "{\"status\": \"Success\"}"exit 0}waitforattach() {shiftattach $*}domountdevice() {MNTPATH=$1DMDEV=$2FSTYPE=$(echo $3|jq -r '.["kubernetes.io/fsType"]')if [ ! -b "${DMDEV}" ]; thenerr "{\"status\": \"Failure\", \"message\": \"${DMDEV} does not exist\"}"exit 1fiif [ $(ismounted) -eq 1 ] ; thenlog "{\"status\": \"Success\"}"exit 0fiVOLFSTYPE=`blkid -o udev ${DMDEV} 2>/dev/null|grep "ID_FS_TYPE"|cut -d"=" -f2`if [ "${VOLFSTYPE}" == "" ]; thenmkfs -t ${FSTYPE} ${DMDEV} >/dev/null 2>&1if [ $? -ne 0 ]; thenerr "{ \"status\": \"Failure\", \"message\": \"Failed to create fs ${FSTYPE} on device ${DMDEV}\"}"exit 1fifimkdir -p ${MNTPATH} &> /dev/nullmount ${DMDEV} ${MNTPATH} &> /dev/nullif [ $? -ne 0 ]; thenerr "{ \"status\": \"Failure\", \"message\": \"Failed to mount device ${DMDEV} at ${MNTPATH}\"}"exit 1filog "{\"status\": \"Success\"}"exit 0}unmountdevice() {MNTPATH=$1if [ ! -d ${MNTPATH} ]; thenlog "{\"status\": \"Success\"}"exit 0fiif [ $(ismounted) -eq 0 ] ; thenlog "{\"status\": \"Success\"}"exit 0fiumount ${MNTPATH} &> /dev/nullif [ $? -ne 0 ]; thenerr "{ \"status\": \"Failed\", \"message\": \"Failed to unmount volume at ${MNTPATH}\"}"exit 1filog "{\"status\": \"Success\"}"exit 0}isattached() {log "{\"status\": \"Success\", \"attached\":true}"exit 0}op=$1if [ "$op" = "init" ]; thenlog "{\"status\": \"Success\"}"exit 0fiif [ $# -lt 2 ]; thenusagefishiftcase "$op" inattach)attach $*;;detach)detach $*;;waitforattach)waitforattach $*;;mountdevice)domountdevice $*;;unmountdevice)unmountdevice $*;;isattached) isattached $* ;;*)log "{ \"status\": \"Not supported\" }"exit 0esacexit 1值得注意的是，为什么会有两次mount操作，一次mountdevice,一次mount。分别是做什么的？
其实k8s提供的volume管理方式是，一个volume可以被多个pod挂载，如果某个device需要作为多个pod的volume，就需要多次挂载。但是device只能被挂载一次。所以，k8s采用的方式是，先用mountdevice将device挂载到一个全局目录，然后这个全局目录就可以被多次挂载到pod的卷目录。如此一来，就能完成多pod挂载同一个volume
AttachVolume：调用attach
DetachVolume：调用detach
MountVolume：调用mountdevice,mount
UnmountVolume：调用unmount
UnmountDevice：调用umountdevice
volume和pod的预期状态不存在绑定关系，则detach volume，并对pod和volume执行unmount操作
volume和pod的预期状态存在绑定关系，则attach volume，并对pod和volume执行mount操作
DesiredStateOfWorld：预期中，pod对volume的使用情况，简称预期状态。当pod.yaml定制好volume，并提交成功，预期状态就已经确定
ActualStateOfWorld：实际中，pod对voluem的使用情况，简称实际状态。实际状态是kubelet的后台线程监控的结果
不断同步apiserver的pod信息，根据新增、删除的pod对volume状态进行同步更新
启动服务，监听controller manager的请求。其中controller manager可以辅助kubelet管理volume，用户也可以选择禁用controller manager的管理
只有理解了volume manager的代码，在使用它提供的volume plugin或者实现自定义flex volume plugin时才能驾轻就熟。以上代码，都是基于k8s v1.6.6版本
以上就是如何理解kubernetes数据卷管理的源码，小编相信有部分知识点可能是我们日常工作会见到或用到的。希望你能通过这篇文章学到更多知识。更多详情敬请关注编程网行业资讯频道。
