如果要开发一个Dynamic Provisioner，需要使用到the helper library。

1. Dynamic Provisioner

1.1. Provisioner Interface

开发Dynamic Provisioner需要实现Provisioner接口，该接口有两个方法，分别是：

Provision：创建存储资源，并且返回一个PV对象。
Delete：移除对应的存储资源，但并没有删除PV对象。

Provisioner 接口源码如下：

// Provisioner is an interface that creates templates for PersistentVolumes
// and can create the volume as a new resource in the infrastructure provider.
// It can also remove the volume it created from the underlying storage
// provider.
type Provisioner interface {
	// Provision creates a volume i.e. the storage asset and returns a PV object
	// for the volume
	Provision(VolumeOptions) (*v1.PersistentVolume, error)
	// Delete removes the storage asset that was created by Provision backing the
	// given PV. Does not delete the PV object itself.
	//
	// May return IgnoredError to indicate that the call has been ignored and no
	// action taken.
	Delete(*v1.PersistentVolume) error
}

1.2. VolumeOptions

Provisioner接口的Provision方法的入参是一个VolumeOptions对象。VolumeOptions对象包含了创建PV对象所需要的信息，例如：PV的回收策略，PV的名字，PV所对应的PVC对象以及PVC的StorageClass对象使用的参数等。

VolumeOptions 源码如下：

// VolumeOptions contains option information about a volume
// https://github.com/kubernetes/kubernetes/blob/release-1.4/pkg/volume/plugins.go
type VolumeOptions struct {
	// Reclamation policy for a persistent volume
	PersistentVolumeReclaimPolicy v1.PersistentVolumeReclaimPolicy
	// PV.Name of the appropriate PersistentVolume. Used to generate cloud
	// volume name.
	PVName string

	// PV mount options. Not validated - mount of the PVs will simply fail if one is invalid.
	MountOptions []string

	// PVC is reference to the claim that lead to provisioning of a new PV.
	// Provisioners *must* create a PV that would be matched by this PVC,
	// i.e. with required capacity, accessMode, labels matching PVC.Selector and
	// so on.
	PVC *v1.PersistentVolumeClaim
	// Volume provisioning parameters from StorageClass
	Parameters map[string]string

	// Node selected by the scheduler for the volume.
	SelectedNode *v1.Node
	// Topology constraint parameter from StorageClass
	AllowedTopologies []v1.TopologySelectorTerm
}

1.3. ProvisionController

ProvisionController是一个给PVC提供PV的控制器，具体执行Provisioner接口的Provision和Delete的方法的所有逻辑。

1.4. 开发provisioner的步骤

写一个provisioner实现Provisioner接口（包含Provision和Delete的方法）。
通过该provisioner构建``ProvisionController`。
执行ProvisionController的Run方法。

2. NFS Client Provisioner

nfs-client-provisioner是一个automatic provisioner，使用NFS作为存储，自动创建PV和对应的PVC，本身不提供NFS存储，需要外部先有一套NFS存储服务。

PV以 ${namespace}-${pvcName}-${pvName}的命名格式提供（在NFS服务器上）
PV回收的时候以 archieved-${namespace}-${pvcName}-${pvName} 的命名格式（在NFS服务器上）

以下通过nfs-client-provisioner的源码分析来说明开发自定义provisioner整个过程。nfs-client-provisioner的主要代码都在provisioner.go的文件中。

nfs-client-provisioner源码地址：https://github.com/kubernetes-incubator/external-storage/tree/master/nfs-client

2.1. Main函数

2.1.1. 读取环境变量

源码如下：

func main() {
	flag.Parse()
	flag.Set("logtostderr", "true")

	server := os.Getenv("NFS_SERVER")
	if server == "" {
		glog.Fatal("NFS_SERVER not set")
	}
	path := os.Getenv("NFS_PATH")
	if path == "" {
		glog.Fatal("NFS_PATH not set")
	}
	provisionerName := os.Getenv(provisionerNameKey)
	if provisionerName == "" {
		glog.Fatalf("environment variable %s is not set! Please set it.", provisionerNameKey)
	}
    ...
}

main函数先获取NFS_SERVER、NFS_PATH、PROVISIONER_NAME三个环境变量的值，因此在部署nfs-client-provisioner的时候，需要将这三个环境变量的值传入。

NFS_SERVER：NFS服务端的IP地址。
NFS_PATH：NFS服务端设置的共享目录
PROVISIONER_NAME：provisioner的名字，需要和StorageClass对象中的provisioner字段一致。

例如StorageClass对象的yaml文件如下：

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: managed-nfs-storage
provisioner: fuseim.pri/ifs # or choose another name, must match deployment's env PROVISIONER_NAME'
parameters:
  archiveOnDelete: "false" # When set to "false" your PVs will not be archived by the provisioner upon deletion of the PVC.

2.1.2. 获取clientset对象

源码如下：

// Create an InClusterConfig and use it to create a client for the controller
// to use to communicate with Kubernetes
config, err := rest.InClusterConfig()
if err != nil {
	glog.Fatalf("Failed to create config: %v", err)
}
clientset, err := kubernetes.NewForConfig(config)
if err != nil {
	glog.Fatalf("Failed to create client: %v", err)
}

通过读取对应的k8s的配置，创建clientset对象，用来执行k8s对应的API，其中主要包括对PV和PVC等对象的创建删除等操作。

2.1.3. 构造nfsProvisioner对象

源码如下：

// The controller needs to know what the server version is because out-of-tree
// provisioners aren't officially supported until 1.5
serverVersion, err := clientset.Discovery().ServerVersion()
if err != nil {
	glog.Fatalf("Error getting server version: %v", err)
}

clientNFSProvisioner := &nfsProvisioner{
	client: clientset,
	server: server,
	path:   path,
}

通过clientset、server、path等值构造nfsProvisioner对象，同时还获取了k8s的版本信息，因为provisioners的功能在k8s 1.5及以上版本才支持。

nfsProvisioner类型定义如下：

type nfsProvisioner struct {
	client kubernetes.Interface
	server string
	path   string
}

var _ controller.Provisioner = &nfsProvisioner{}

nfsProvisioner是一个自定义的provisioner，用来实现Provisioner的接口，其中的属性除了server、path这两个关于NFS相关的参数，还包含了client，主要用来调用k8s的API。

var _ controller.Provisioner = &nfsProvisioner{}

以上用法用来检测nfsProvisioner是否实现了Provisioner的接口。

2.1.4. 构建并运行ProvisionController

源码如下：

// Start the provision controller which will dynamically provision efs NFS
// PVs
pc := controller.NewProvisionController(clientset, provisionerName, clientNFSProvisioner, serverVersion.GitVersion)
pc.Run(wait.NeverStop)

通过nfsProvisioner构造ProvisionController对象并执行Run方法，ProvisionController实现了具体的PV和PVC的相关逻辑，Run方法以常驻进程的方式运行。

2.2. Provision和Delete方法

2.2.1. Provision方法

nfsProvisioner的Provision方法具体源码参考：https://github.com/kubernetes-incubator/external-storage/blob/master/nfs-client/cmd/nfs-client-provisioner/provisioner.go#L56

Provision方法用来创建存储资源，并且返回一个PV对象。其中入参是VolumeOptions，用来指定PV对象的相关属性。

1、构建PV和PVC的名称

func (p *nfsProvisioner) Provision(options controller.VolumeOptions) (*v1.PersistentVolume, error) {
	if options.PVC.Spec.Selector != nil {
		return nil, fmt.Errorf("claim Selector is not supported")
	}
	glog.V(4).Infof("nfs provisioner: VolumeOptions %v", options)

	pvcNamespace := options.PVC.Namespace
	pvcName := options.PVC.Name

	pvName := strings.Join([]string{pvcNamespace, pvcName, options.PVName}, "-")

	fullPath := filepath.Join(mountPath, pvName)
	glog.V(4).Infof("creating path %s", fullPath)
	if err := os.MkdirAll(fullPath, 0777); err != nil {
		return nil, errors.New("unable to create directory to provision new pv: " + err.Error())
	}
	os.Chmod(fullPath, 0777)

	path := filepath.Join(p.path, pvName)
    ...
}

通过VolumeOptions的入参，构建PV和PVC的名称，以及创建路径path。

2、构造PV对象

pv := &v1.PersistentVolume{
	ObjectMeta: metav1.ObjectMeta{
		Name: options.PVName,
	},
	Spec: v1.PersistentVolumeSpec{
		PersistentVolumeReclaimPolicy: options.PersistentVolumeReclaimPolicy,
		AccessModes:                   options.PVC.Spec.AccessModes,
		MountOptions:                  options.MountOptions,
		Capacity: v1.ResourceList{
			v1.ResourceName(v1.ResourceStorage): options.PVC.Spec.Resources.Requests[v1.ResourceName(v1.ResourceStorage)],
		},
		PersistentVolumeSource: v1.PersistentVolumeSource{
			NFS: &v1.NFSVolumeSource{
				Server:   p.server,
				Path:     path,
				ReadOnly: false,
			},
		},
	},
}
return pv, nil

综上可以看出，Provision方法只是通过VolumeOptions参数来构建PV对象，并没有执行具体PV的创建或删除的操作。

不同类型的Provisioner的，一般是PersistentVolumeSource类型和参数不同，例如nfs-provisioner对应的PersistentVolumeSource为NFS，并且需要传入NFS相关的参数：Server，Path等。

2.2.2. Delete方法

nfsProvisioner的delete方法具体源码参考：https://github.com/kubernetes-incubator/external-storage/blob/master/nfs-client/cmd/nfs-client-provisioner/provisioner.go#L99

1、获取pvName和path等相关参数

func (p *nfsProvisioner) Delete(volume *v1.PersistentVolume) error {
	path := volume.Spec.PersistentVolumeSource.NFS.Path
	pvName := filepath.Base(path)
	oldPath := filepath.Join(mountPath, pvName)
	if _, err := os.Stat(oldPath); os.IsNotExist(err) {
		glog.Warningf("path %s does not exist, deletion skipped", oldPath)
		return nil
	}
    ...
}

通过path和pvName生成oldPath，其中oldPath是原先NFS服务器上pod对应的数据持久化存储路径。

2、获取archiveOnDelete参数并删除数据

// Get the storage class for this volume.
storageClass, err := p.getClassForVolume(volume)
if err != nil {
	return err
}
// Determine if the "archiveOnDelete" parameter exists.
// If it exists and has a falsey value, delete the directory.
// Otherwise, archive it.
archiveOnDelete, exists := storageClass.Parameters["archiveOnDelete"]
if exists {
	archiveBool, err := strconv.ParseBool(archiveOnDelete)
	if err != nil {
		return err
	}
	if !archiveBool {
		return os.RemoveAll(oldPath)
	}
}

如果storageClass对象中指定archiveOnDelete参数并且值为false，则会自动删除oldPath下的所有数据，即pod对应的数据持久化存储数据。

archiveOnDelete字面意思为删除时是否存档，false表示不存档，即删除数据，true表示存档，即重命名路径。

3、重命名旧数据路径

archivePath := filepath.Join(mountPath, "archived-"+pvName)
glog.V(4).Infof("archiving path %s to %s", oldPath, archivePath)
return os.Rename(oldPath, archivePath)

如果storageClass对象中没有指定archiveOnDelete参数或者值为true，表明需要删除时存档，即将oldPath重命名，命名格式为oldPath前面增加archived-的前缀。

3. ProvisionController

3.1. ProvisionController结构体

源码具体参考：https://github.com/kubernetes-incubator/external-storage/blob/master/lib/controller/controller.go#L82

ProvisionController是一个给PVC提供PV的控制器，具体执行Provisioner接口的Provision和Delete的方法的所有逻辑。

3.1.1. 入参

// ProvisionController is a controller that provisions PersistentVolumes for
// PersistentVolumeClaims.
type ProvisionController struct {
	client kubernetes.Interface

	// The name of the provisioner for which this controller dynamically
	// provisions volumes. The value of annDynamicallyProvisioned and
	// annStorageProvisioner to set & watch for, respectively
	provisionerName string

	// The provisioner the controller will use to provision and delete volumes.
	// Presumably this implementer of Provisioner carries its own
	// volume-specific options and such that it needs in order to provision
	// volumes.
	provisioner Provisioner

	// Kubernetes cluster server version:
	// * 1.4: storage classes introduced as beta. Technically out-of-tree dynamic
	// provisioning is not officially supported, though it works
	// * 1.5: storage classes stay in beta. Out-of-tree dynamic provisioning is
	// officially supported
	// * 1.6: storage classes enter GA
	kubeVersion *utilversion.Version
    ...
}

client、provisionerName、provisioner、kubeVersion等属性作为NewProvisionController的入参。

client：clientset客户端，用来调用k8s的API。
provisionerName：provisioner的名字，需要和StorageClass对象中的provisioner字段一致。
provisioner：具体的provisioner的实现者，本文为nfsProvisioner。
kubeVersion：k8s的版本信息。

3.1.2. Controller和Informer

type ProvisionController struct {
	...
	claimInformer    cache.SharedInformer
	claims           cache.Store
	claimController  cache.Controller
	volumeInformer   cache.SharedInformer
	volumes          cache.Store
	volumeController cache.Controller
	classInformer    cache.SharedInformer
	classes          cache.Store
	classController  cache.Controller
    ...
}

ProvisionController结构体中包含了PV、PVC、StorageClass三个对象的Controller、Informer和Store，主要用来执行这三个对象的相关操作。

Controller：通用的控制框架
Informer：消息通知器
Store：通用的对象存储接口

3.1.3. workqueue

type ProvisionController struct {
    ...
	claimQueue  workqueue.RateLimitingInterface
	volumeQueue workqueue.RateLimitingInterface
    ...
}

claimQueue和volumeQueue分别是PV和PVC的任务队列。

3.1.4. 其他

// Identity of this controller, generated at creation time and not persisted
// across restarts. Useful only for debugging, for seeing the source of
// events. controller.provisioner may have its own, different notion of
// identity which may/may not persist across restarts
id            string
component     string
eventRecorder record.EventRecorder

resyncPeriod time.Duration

exponentialBackOffOnError bool
threadiness               int

createProvisionedPVRetryCount int
createProvisionedPVInterval   time.Duration

failedProvisionThreshold, failedDeleteThreshold int

// The port for metrics server to serve on.
metricsPort int32
// The IP address for metrics server to serve on.
metricsAddress string
// The path of metrics endpoint path.
metricsPath string

// Parameters of leaderelection.LeaderElectionConfig.
leaseDuration, renewDeadline, retryPeriod time.Duration

hasRun     bool
hasRunLock *sync.Mutex

3.2. NewProvisionController方法

源码地址：https://github.com/kubernetes-incubator/external-storage/blob/master/lib/controller/controller.go#L383

NewProvisionController方法主要用来构造ProvisionController。

3.2.1. 初始化默认值

// NewProvisionController creates a new provision controller using
// the given configuration parameters and with private (non-shared) informers.
func NewProvisionController(
	client kubernetes.Interface,
	provisionerName string,
	provisioner Provisioner,
	kubeVersion string,
	options ...func(*ProvisionController) error,
) *ProvisionController {
	...
	controller := &ProvisionController{
		client:                        client,
		provisionerName:               provisionerName,
		provisioner:                   provisioner,
		kubeVersion:                   utilversion.MustParseSemantic(kubeVersion),
		id:                            id,
		component:                     component,
		eventRecorder:                 eventRecorder,
		resyncPeriod:                  DefaultResyncPeriod,
		exponentialBackOffOnError:     DefaultExponentialBackOffOnError,
		threadiness:                   DefaultThreadiness,
		createProvisionedPVRetryCount: DefaultCreateProvisionedPVRetryCount,
		createProvisionedPVInterval:   DefaultCreateProvisionedPVInterval,
		failedProvisionThreshold:      DefaultFailedProvisionThreshold,
		failedDeleteThreshold:         DefaultFailedDeleteThreshold,
		leaseDuration:                 DefaultLeaseDuration,
		renewDeadline:                 DefaultRenewDeadline,
		retryPeriod:                   DefaultRetryPeriod,
		metricsPort:                   DefaultMetricsPort,
		metricsAddress:                DefaultMetricsAddress,
		metricsPath:                   DefaultMetricsPath,
		hasRun:                        false,
		hasRunLock:                    &sync.Mutex{},
	}
    ...
}

3.2.2. 初始化任务队列

ratelimiter := workqueue.NewMaxOfRateLimiter(
	workqueue.NewItemExponentialFailureRateLimiter(15*time.Second, 1000*time.Second),
	&workqueue.BucketRateLimiter{Limiter: rate.NewLimiter(rate.Limit(10), 100)},
)
if !controller.exponentialBackOffOnError {
	ratelimiter = workqueue.NewMaxOfRateLimiter(
		workqueue.NewItemExponentialFailureRateLimiter(15*time.Second, 15*time.Second),
		&workqueue.BucketRateLimiter{Limiter: rate.NewLimiter(rate.Limit(10), 100)},
	)
}
controller.claimQueue = workqueue.NewNamedRateLimitingQueue(ratelimiter, "claims")
controller.volumeQueue = workqueue.NewNamedRateLimitingQueue(ratelimiter, "volumes")

3.2.3. ListWatch

// PVC
claimSource := &cache.ListWatch{
	ListFunc: func(options metav1.ListOptions) (runtime.Object, error) {
		return client.CoreV1().PersistentVolumeClaims(v1.NamespaceAll).List(options)
	},
	WatchFunc: func(options metav1.ListOptions) (watch.Interface, error) {
		return client.CoreV1().PersistentVolumeClaims(v1.NamespaceAll).Watch(options)
	},
}
// PV
volumeSource := &cache.ListWatch{
	ListFunc: func(options metav1.ListOptions) (runtime.Object, error) {
		return client.CoreV1().PersistentVolumes().List(options)
	},
	WatchFunc: func(options metav1.ListOptions) (watch.Interface, error) {
		return client.CoreV1().PersistentVolumes().Watch(options)
	},
}
// StorageClass
classSource = &cache.ListWatch{
	ListFunc: func(options metav1.ListOptions) (runtime.Object, error) {
		return client.StorageV1().StorageClasses().List(options)
	},
	WatchFunc: func(options metav1.ListOptions) (watch.Interface, error) {
		return client.StorageV1().StorageClasses().Watch(options)
	},
}

list-watch机制是k8s中用来监听对象变化的核心机制，ListWatch包含ListFunc和WatchFunc两个函数，且不能为空，以上代码分别构造了PV、PVC、StorageClass三个对象的ListWatch结构体。该机制的实现在client-go的cache包中，具体参考：https://godoc.org/k8s.io/client-go/tools/cache。

更多ListWatch代码如下:

具体参考：https://github.com/kubernetes-incubator/external-storage/blob/89b0aaf6413b249b37834b124fc314ef7b8ee949/vendor/k8s.io/client-go/tools/cache/listwatch.go#L34

// ListerWatcher is any object that knows how to perform an initial list and start a watch on a resource.
type ListerWatcher interface {
	// List should return a list type object; the Items field will be extracted, and the
	// ResourceVersion field will be used to start the watch in the right place.
	List(options metav1.ListOptions) (runtime.Object, error)
	// Watch should begin a watch at the specified version.
	Watch(options metav1.ListOptions) (watch.Interface, error)
}

// ListFunc knows how to list resources
type ListFunc func(options metav1.ListOptions) (runtime.Object, error)

// WatchFunc knows how to watch resources
type WatchFunc func(options metav1.ListOptions) (watch.Interface, error)

// ListWatch knows how to list and watch a set of apiserver resources.  It satisfies the ListerWatcher interface.
// It is a convenience function for users of NewReflector, etc.
// ListFunc and WatchFunc must not be nil
type ListWatch struct {
	ListFunc  ListFunc
	WatchFunc WatchFunc
	// DisableChunking requests no chunking for this list watcher.
	DisableChunking bool
}

3.2.4. ResourceEventHandlerFuncs

// PVC
claimHandler := cache.ResourceEventHandlerFuncs{
	AddFunc:    func(obj interface{}) { controller.enqueueWork(controller.claimQueue, obj) },
	UpdateFunc: func(oldObj, newObj interface{}) { controller.enqueueWork(controller.claimQueue, newObj) },
	DeleteFunc: func(obj interface{}) { controller.forgetWork(controller.claimQueue, obj) },
}
// PV
volumeHandler := cache.ResourceEventHandlerFuncs{
	AddFunc:    func(obj interface{}) { controller.enqueueWork(controller.volumeQueue, obj) },
	UpdateFunc: func(oldObj, newObj interface{}) { controller.enqueueWork(controller.volumeQueue, newObj) },
	DeleteFunc: func(obj interface{}) { controller.forgetWork(controller.volumeQueue, obj) },
}
// StorageClass
classHandler := cache.ResourceEventHandlerFuncs{
	// We don't need an actual event handler for StorageClasses,
	// but we must pass a non-nil one to cache.NewInformer()
	AddFunc:    nil,
	UpdateFunc: nil,
	DeleteFunc: nil,
}

ResourceEventHandlerFuncs是资源事件处理函数，主要用来对k8s资源对象增删改变化的事件进行消息通知，该函数实现了ResourceEventHandler的接口。具体代码逻辑在client-go的cache包中。

更多ResourceEventHandlerFuncs代码可参考：

// ResourceEventHandler can handle notifications for events that happen to a
// resource. The events are informational only, so you can't return an
// error.
//  * OnAdd is called when an object is added.
//  * OnUpdate is called when an object is modified. Note that oldObj is the
//      last known state of the object-- it is possible that several changes
//      were combined together, so you can't use this to see every single
//      change. OnUpdate is also called when a re-list happens, and it will
//      get called even if nothing changed. This is useful for periodically
//      evaluating or syncing something.
//  * OnDelete will get the final state of the item if it is known, otherwise
//      it will get an object of type DeletedFinalStateUnknown. This can
//      happen if the watch is closed and misses the delete event and we don't
//      notice the deletion until the subsequent re-list.
type ResourceEventHandler interface {
	OnAdd(obj interface{})
	OnUpdate(oldObj, newObj interface{})
	OnDelete(obj interface{})
}

// ResourceEventHandlerFuncs is an adaptor to let you easily specify as many or
// as few of the notification functions as you want while still implementing
// ResourceEventHandler.
type ResourceEventHandlerFuncs struct {
	AddFunc    func(obj interface{})
	UpdateFunc func(oldObj, newObj interface{})
	DeleteFunc func(obj interface{})
}

3.2.5. 构造Store和Controller

1、PVC

if controller.claimInformer != nil {
	controller.claimInformer.AddEventHandlerWithResyncPeriod(claimHandler, controller.resyncPeriod)
	controller.claims, controller.claimController =
		controller.claimInformer.GetStore(),
		controller.claimInformer.GetController()
} else {
	controller.claims, controller.claimController =
		cache.NewInformer(
			claimSource,
			&v1.PersistentVolumeClaim{},
			controller.resyncPeriod,
			claimHandler,
		)
}

2、PV

if controller.volumeInformer != nil {
	controller.volumeInformer.AddEventHandlerWithResyncPeriod(volumeHandler, controller.resyncPeriod)
	controller.volumes, controller.volumeController =
		controller.volumeInformer.GetStore(),
		controller.volumeInformer.GetController()
} else {
	controller.volumes, controller.volumeController =
		cache.NewInformer(
			volumeSource,
			&v1.PersistentVolume{},
			controller.resyncPeriod,
			volumeHandler,
		)
}

3、StorageClass

if controller.classInformer != nil {
	// no resource event handler needed for StorageClasses
	controller.classes, controller.classController =
		controller.classInformer.GetStore(),
		controller.classInformer.GetController()
} else {
	controller.classes, controller.classController = cache.NewInformer(
		classSource,
		versionedClassType,
		controller.resyncPeriod,
		classHandler,
	)
}

通过cache.NewInformer的方法构造，入参是ListWatch结构体和ResourceEventHandlerFuncs函数等，返回值是Store和Controller。

通过以上各个部分的构造，最后返回一个具体的ProvisionController对象。

3.3. ProvisionController.Run方法

ProvisionController的Run方法是以常驻进程的方式运行，函数内部再运行其他的controller。

3.3.1. prometheus数据收集

// Run starts all of this controller's control loops
func (ctrl *ProvisionController) Run(stopCh <-chan struct{}) {

	run := func(stopCh <-chan struct{}) {
		...
		if ctrl.metricsPort > 0 {
			prometheus.MustRegister([]prometheus.Collector{
				metrics.PersistentVolumeClaimProvisionTotal,
				metrics.PersistentVolumeClaimProvisionFailedTotal,
				metrics.PersistentVolumeClaimProvisionDurationSeconds,
				metrics.PersistentVolumeDeleteTotal,
				metrics.PersistentVolumeDeleteFailedTotal,
				metrics.PersistentVolumeDeleteDurationSeconds,
			}...)
			http.Handle(ctrl.metricsPath, promhttp.Handler())
			address := net.JoinHostPort(ctrl.metricsAddress, strconv.FormatInt(int64(ctrl.metricsPort), 10))
			glog.Infof("Starting metrics server at %s\n", address)
			go wait.Forever(func() {
				err := http.ListenAndServe(address, nil)
				if err != nil {
					glog.Errorf("Failed to listen on %s: %v", address, err)
				}
			}, 5*time.Second)
		}
        ...
}

3.3.2. Controller.Run

// If a SharedInformer has been passed in, this controller should not
// call Run again
if ctrl.claimInformer == nil {
	go ctrl.claimController.Run(stopCh)
}
if ctrl.volumeInformer == nil {
	go ctrl.volumeController.Run(stopCh)
}
if ctrl.classInformer == nil {
	go ctrl.classController.Run(stopCh)
}

运行消息通知器Informer。

3.3.3. Worker

for i := 0; i < ctrl.threadiness; i++ {
	go wait.Until(ctrl.runClaimWorker, time.Second, stopCh)
	go wait.Until(ctrl.runVolumeWorker, time.Second, stopCh)
}

runClaimWorker和runVolumeWorker分别为PVC和PV的worker，这两个的具体执行体分别是processNextClaimWorkItem和processNextVolumeWorkItem。

执行流程如下：

PVC的函数调用流程

runClaimWorker→processNextClaimWorkItem→syncClaimHandler→syncClaim→provisionClaimOperation

PV的函数调用流程

runVolumeWorker→processNextVolumeWorkItem→syncVolumeHandler→syncVolume→deleteVolumeOperation

可见最后执行的函数分别是provisionClaimOperation和deleteVolumeOperation。

3.4. Operation

3.4.1. provisionClaimOperation

1、provisionClaimOperation入参是PVC，通过PVC获得PV对象，并判断PV对象是否存在，如果存在则退出后续操作。

// provisionClaimOperation attempts to provision a volume for the given claim.
// Returns error, which indicates whether provisioning should be retried
// (requeue the claim) or not
func (ctrl *ProvisionController) provisionClaimOperation(claim *v1.PersistentVolumeClaim) error {
	// Most code here is identical to that found in controller.go of kube's PV controller...
	claimClass := helper.GetPersistentVolumeClaimClass(claim)
	operation := fmt.Sprintf("provision %q class %q", claimToClaimKey(claim), claimClass)
	glog.Infof(logOperation(operation, "started"))

	//  A previous doProvisionClaim may just have finished while we were waiting for
	//  the locks. Check that PV (with deterministic name) hasn't been provisioned
	//  yet.
	pvName := ctrl.getProvisionedVolumeNameForClaim(claim)
	volume, err := ctrl.client.CoreV1().PersistentVolumes().Get(pvName, metav1.GetOptions{})
	if err == nil && volume != nil {
		// Volume has been already provisioned, nothing to do.
		glog.Infof(logOperation(operation, "persistentvolume %q already exists, skipping", pvName))
		return nil
	}
    ...
}

2、获取StorageClass对象中的Provisioner和ReclaimPolicy参数，如果provisionerName和StorageClass对象中的provisioner字段不一致则报错并退出执行。

provisioner, parameters, err := ctrl.getStorageClassFields(claimClass)
if err != nil {
	glog.Errorf(logOperation(operation, "error getting claim's StorageClass's fields: %v", err))
	return nil
}
if provisioner != ctrl.provisionerName {
	// class.Provisioner has either changed since shouldProvision() or
	// annDynamicallyProvisioned contains different provisioner than
	// class.Provisioner.
	glog.Errorf(logOperation(operation, "unknown provisioner %q requested in claim's StorageClass", provisioner))
	return nil
}
// Check if this provisioner can provision this claim.
if err = ctrl.canProvision(claim); err != nil {
	ctrl.eventRecorder.Event(claim, v1.EventTypeWarning, "ProvisioningFailed", err.Error())
	glog.Errorf(logOperation(operation, "failed to provision volume: %v", err))
	return nil
}

reclaimPolicy := v1.PersistentVolumeReclaimDelete
if ctrl.kubeVersion.AtLeast(utilversion.MustParseSemantic("v1.8.0")) {
	reclaimPolicy, err = ctrl.fetchReclaimPolicy(claimClass)
	if err != nil {
		return err
	}
}

3、执行具体的provisioner.Provision方法，构建PV对象，例如本文中的provisioner是nfs-provisioner。

options := VolumeOptions{
	PersistentVolumeReclaimPolicy: reclaimPolicy,
	PVName:            pvName,
	PVC:               claim,
	MountOptions:      mountOptions,
	Parameters:        parameters,
	SelectedNode:      selectedNode,
	AllowedTopologies: allowedTopologies,
}

ctrl.eventRecorder.Event(claim, v1.EventTypeNormal, "Provisioning", fmt.Sprintf("External provisioner is provisioning volume for claim %q", claimToClaimKey(claim)))

volume, err = ctrl.provisioner.Provision(options)
if err != nil {
	if ierr, ok := err.(*IgnoredError); ok {
		// Provision ignored, do nothing and hope another provisioner will provision it.
		glog.Infof(logOperation(operation, "volume provision ignored: %v", ierr))
		return nil
	}
	err = fmt.Errorf("failed to provision volume with StorageClass %q: %v", claimClass, err)
	ctrl.eventRecorder.Event(claim, v1.EventTypeWarning, "ProvisioningFailed", err.Error())
	return err
}

4、创建k8s的PV对象。

// Try to create the PV object several times
for i := 0; i < ctrl.createProvisionedPVRetryCount; i++ {
	glog.Infof(logOperation(operation, "trying to save persistentvvolume %q", volume.Name))
	if _, err = ctrl.client.CoreV1().PersistentVolumes().Create(volume); err == nil || apierrs.IsAlreadyExists(err) {
		// Save succeeded.
		if err != nil {
			glog.Infof(logOperation(operation, "persistentvolume %q already exists, reusing", volume.Name))
			err = nil
		} else {
			glog.Infof(logOperation(operation, "persistentvolume %q saved", volume.Name))
		}
		break
	}
	// Save failed, try again after a while.
	glog.Infof(logOperation(operation, "failed to save persistentvolume %q: %v", volume.Name, err))
	time.Sleep(ctrl.createProvisionedPVInterval)
}

5、创建PV失败，清理存储资源。

if err != nil {
	// Save failed. Now we have a storage asset outside of Kubernetes,
	// but we don't have appropriate PV object for it.
	// Emit some event here and try to delete the storage asset several
	// times.
	...
	for i := 0; i < ctrl.createProvisionedPVRetryCount; i++ {
		if err = ctrl.provisioner.Delete(volume); err == nil {
			// Delete succeeded
			glog.Infof(logOperation(operation, "cleaning volume %q succeeded", volume.Name))
			break
		}
		// Delete failed, try again after a while.
		glog.Infof(logOperation(operation, "failed to clean volume %q: %v", volume.Name, err))
		time.Sleep(ctrl.createProvisionedPVInterval)
	}
	if err != nil {
		// Delete failed several times. There is an orphaned volume and there
		// is nothing we can do about it.
		strerr := fmt.Sprintf("Error cleaning provisioned volume for claim %s: %v. Please delete manually.", claimToClaimKey(claim), err)
		glog.Error(logOperation(operation, strerr))
		ctrl.eventRecorder.Event(claim, v1.EventTypeWarning, "ProvisioningCleanupFailed", strerr)
	}
}

如果创建成功，则打印成功的日志，并返回nil。

3.4.2. deleteVolumeOperation

1、deleteVolumeOperation入参是PV，先获得PV对象，并判断是否需要删除。

// deleteVolumeOperation attempts to delete the volume backing the given
// volume. Returns error, which indicates whether deletion should be retried
// (requeue the volume) or not
func (ctrl *ProvisionController) deleteVolumeOperation(volume *v1.PersistentVolume) error {
	...
	// This method may have been waiting for a volume lock for some time.
	// Our check does not have to be as sophisticated as PV controller's, we can
	// trust that the PV controller has set the PV to Released/Failed and it's
	// ours to delete
	newVolume, err := ctrl.client.CoreV1().PersistentVolumes().Get(volume.Name, metav1.GetOptions{})
	if err != nil {
		return nil
	}
	if !ctrl.shouldDelete(newVolume) {
		glog.Infof(logOperation(operation, "persistentvolume no longer needs deletion, skipping"))
		return nil
	}
    ...
}

2、调用具体的provisioner的Delete方法，例如，如果是nfs-provisioner，则是调用nfs-provisioner的Delete方法。

err = ctrl.provisioner.Delete(volume)
if err != nil {
	if ierr, ok := err.(*IgnoredError); ok {
		// Delete ignored, do nothing and hope another provisioner will delete it.
		glog.Infof(logOperation(operation, "volume deletion ignored: %v", ierr))
		return nil
	}
	// Delete failed, emit an event.
	glog.Errorf(logOperation(operation, "volume deletion failed: %v", err))
	ctrl.eventRecorder.Event(volume, v1.EventTypeWarning, "VolumeFailedDelete", err.Error())
	return err
}

3、删除k8s中的PV对象。

// Delete the volume
if err = ctrl.client.CoreV1().PersistentVolumes().Delete(volume.Name, nil); err != nil {
	// Oops, could not delete the volume and therefore the controller will
	// try to delete the volume again on next update.
	glog.Infof(logOperation(operation, "failed to delete persistentvolume: %v", err))
	return err
}

4. 总结

Provisioner接口包含Provision和Delete两个方法，自定义的provisioner需要实现这两个方法，这两个方法只是处理了跟存储类型相关的事项，并没有针对PV、PVC对象的增删等操作。
Provision方法主要用来构造PV对象，不同类型的Provisioner的，一般是PersistentVolumeSource类型和参数不同，例如nfs-provisioner对应的PersistentVolumeSource为NFS，并且需要传入NFS相关的参数：Server，Path等。
Delete方法主要针对对应的存储类型，做数据存档（备份）或删除的处理。
StorageClass对象需要单独创建，用来指定具体的provisioner来执行相关逻辑。
provisionClaimOperation和deleteVolumeOperation具体执行了k8s中PV对象的创建和删除操作，同时调用了具体provisioner的Provision和Delete两个方法来对存储数据做处理。

参考文章

https://github.com/kubernetes-incubator/external-storage/tree/master/docs/demo/hostpath-provisioner
https://github.com/kubernetes-incubator/external-storage/tree/master/nfs-client
https://github.com/kubernetes-incubator/external-storage/blob/master/lib/controller/controller.go
https://github.com/kubernetes-incubator/external-storage/blob/master/lib/controller/volume.go

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nfs-client-provisioner.md

nfs-client-provisioner.md

1. Dynamic Provisioner

1.1. Provisioner Interface

1.2. VolumeOptions

1.3. ProvisionController

1.4. 开发provisioner的步骤

2. NFS Client Provisioner

2.1. Main函数

2.1.1. 读取环境变量

2.1.2. 获取clientset对象

2.1.3. 构造nfsProvisioner对象

2.1.4. 构建并运行ProvisionController

2.2. Provision和Delete方法

2.2.1. Provision方法

2.2.2. Delete方法

3. ProvisionController

3.1. ProvisionController结构体

3.1.1. 入参

3.1.2. Controller和Informer

3.1.3. workqueue

3.1.4. 其他

3.2. NewProvisionController方法

3.2.1. 初始化默认值

3.2.2. 初始化任务队列

3.2.3. ListWatch

3.2.4. ResourceEventHandlerFuncs

3.2.5. 构造Store和Controller

3.3. ProvisionController.Run方法

3.3.1. prometheus数据收集

3.3.2. Controller.Run

3.3.3. Worker

3.4. Operation

3.4.1. provisionClaimOperation

3.4.2. deleteVolumeOperation

4. 总结

Files

nfs-client-provisioner.md

Latest commit

History

nfs-client-provisioner.md

File metadata and controls

1. Dynamic Provisioner

1.1. Provisioner Interface

1.2. VolumeOptions

1.3. ProvisionController

1.4. 开发provisioner的步骤

2. NFS Client Provisioner

2.1. Main函数

2.1.1. 读取环境变量

2.1.2. 获取clientset对象

2.1.3. 构造nfsProvisioner对象

2.1.4. 构建并运行ProvisionController

2.2. Provision和Delete方法

2.2.1. Provision方法

2.2.2. Delete方法

3. ProvisionController

3.1. ProvisionController结构体

3.1.1. 入参

3.1.2. Controller和Informer

3.1.3. workqueue

3.1.4. 其他

3.2. NewProvisionController方法

3.2.1. 初始化默认值

3.2.2. 初始化任务队列

3.2.3. ListWatch

3.2.4. ResourceEventHandlerFuncs

3.2.5. 构造Store和Controller

3.3. ProvisionController.Run方法

3.3.1. prometheus数据收集

3.3.2. Controller.Run

3.3.3. Worker

3.4. Operation

3.4.1. provisionClaimOperation

3.4.2. deleteVolumeOperation

4. 总结