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) error
GetMountedVolumesForPod(podName types.UniquePodName) container.VolumeMap
GetExtraSupplementalGroupsForPod(pod *v1.Pod) []int64
GetVolumesInUse() []v1.UniqueVolumeName
ReconcilerStatesHasBeenSynced() bool
VolumeIsAttached(volumeName v1.UniqueVolumeName) bool
MarkVolumesAsReportedInUse(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)
<-stopCh
glog.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() {
//umount
for _, mountedVolume := range rc.actualStateOfWorld.GetMountedVolumes() {
if !rc.desiredStateOfWorld.PodExistsInVolume(mountedVolume.PodName, mountedVolume.VolumeName) {
...
err := rc.operationExecutor.UnmountVolume(
mountedVolume.MountedVolume, rc.actualStateOfWorld)
...
}
}
// attach/mount
for _, volumeToMount := range rc.desiredStateOfWorld.GetVolumesToMount() {
volMounted, devicePath, err := rc.actualStateOfWorld.PodExistsInVolume(volumeToMount.PodName, volumeToMount.VolumeName)
volumeToMount.DevicePath = devicePath
if 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/unmount
for _, 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 "
err "\t$0 detach "
err "\t$0 waitforattach "
err "\t$0 mountdevice "
err "\t$0 unmountdevice "
err "\t$0 isattached "
exit 1
}
err() {
echo -ne $* 1>&2
}
log() {
echo -ne $* >&1
}
ismounted() {
MOUNT=`findmnt -n ${MNTPATH} 2>/dev/null | cut -d' ' -f1`
if [ "${MOUNT}" == "${MNTPATH}" ]; then
echo "1"
else
echo "0"
fi
}
getdevice() {
VOLUMEID=$(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=$1
SIZE=$(echo $1 | jq -r '.size')
DMDEV=$(getdevice)
if [ ! -b "${DMDEV}" ]; then
err "{\"status\": \"Failure\", \"message\": \"Volume ${VOLUMEID} does not exist\"}"
exit 1
fi
log "{\"status\": \"Success\", \"device\":\"${DMDEV}\"}"
exit 0
}
detach() {
log "{\"status\": \"Success\"}"
exit 0
}
waitforattach() {
shift
attach $*
}
domountdevice() {
MNTPATH=$1
DMDEV=$2
FSTYPE=$(echo $3|jq -r '.["kubernetes.io/fsType"]')
if [ ! -b "${DMDEV}" ]; then
err "{\"status\": \"Failure\", \"message\": \"${DMDEV} does not exist\"}"
exit 1
fi
if [ $(ismounted) -eq 1 ] ; then
log "{\"status\": \"Success\"}"
exit 0
fi
VOLFSTYPE=`blkid -o udev ${DMDEV} 2>/dev/null|grep "ID_FS_TYPE"|cut -d"=" -f2`
if [ "${VOLFSTYPE}" == "" ]; then
mkfs -t ${FSTYPE} ${DMDEV} >/dev/null 2>&1
if [ $? -ne 0 ]; then
err "{ \"status\": \"Failure\", \"message\": \"Failed to create fs ${FSTYPE} on device ${DMDEV}\"}"
exit 1
fi
fi
mkdir -p ${MNTPATH} &> /dev/null
mount ${DMDEV} ${MNTPATH} &> /dev/null
if [ $? -ne 0 ]; then
err "{ \"status\": \"Failure\", \"message\": \"Failed to mount device ${DMDEV} at ${MNTPATH}\"}"
exit 1
fi
log "{\"status\": \"Success\"}"
exit 0
}
unmountdevice() {
MNTPATH=$1
if [ ! -d ${MNTPATH} ]; then
log "{\"status\": \"Success\"}"
exit 0
fi
if [ $(ismounted) -eq 0 ] ; then
log "{\"status\": \"Success\"}"
exit 0
fi
umount ${MNTPATH} &> /dev/null
if [ $? -ne 0 ]; then
err "{ \"status\": \"Failed\", \"message\": \"Failed to unmount volume at ${MNTPATH}\"}"
exit 1
fi
log "{\"status\": \"Success\"}"
exit 0
}
isattached() {
log "{\"status\": \"Success\", \"attached\":true}"
exit 0
}
op=$1
if [ "$op" = "init" ]; then
log "{\"status\": \"Success\"}"
exit 0
fi
if [ $# -lt 2 ]; then
usage
fi
shift
case "$op" in
attach)
attach $*
;;
detach)
detach $*
;;
waitforattach)
waitforattach $*
;;
mountdevice)
domountdevice $*
;;
unmountdevice)
unmountdevice $*
;;
isattached)
isattached $*
;;
*)
log "{ \"status\": \"Not supported\" }"
exit 0
esac
exit 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
