external-resizer 源码分析/pvc 扩容分析

阅读原文时间：2021年07月18日阅读：1

基于tag v0.5.0

https://github.com/kubernetes-csi/external-resizer/releases/tag/v0.5.0

存储扩容分为controller端和node端两步，先进行controller端（external-resizer触发）的扩容，然后再进行node端（kubelet触发）扩容（当volumemode是block，则不用进行node端扩容操作），存储的扩容操作才算完成。

controller端存储扩容作用

将底层存储扩容，如ceph rbd扩容，则会让ceph集群中的rbd image扩容。

node端存储扩容作用

在pod所在的node上做相应的操作，让node感知该存储已经扩容，如ceph rbd filesystem扩容，则会调用node上的文件系统扩容命令让文件系统扩容。

某些存储无需进行node端扩容操作如cephfs。

存储扩容大致过程

（1）更改pvc.Spec.Resources.Requests.storgage，触发扩容

（2）controller端存储扩容：external-resizer watch pvc对象，当发现pvc.Spec.Resources.Requests.storgage比pvc.Status.Capacity.storgage大，于是调csi plugin的ControllerExpandVolume方法进行 controller端扩容，进行底层存储扩容，并更新pv.Spec.Capacity.storgage。

（3）node端存储扩容：kubelet发现pv.Spec.Capacity.storage大于pvc.Status.Capacity.storage，于是调csi node端扩容，对dnode上文件系统扩容，成功后kubelet更新pvc.Status.Capacity.storage。

存储扩容详细过程

下面以ceph rbd存储扩容为例，对详细的存储扩容过程进行分析。

（1）修改pvc对象，修改申请存储大小（pvc.spec.resources.requests.storage）；

（2）修改成功后，external-resizer监听到该pvc的update事件，发现pvc.Spec.Resources.Requests.storgage比pvc.Status.Capacity.storgage大，于是调ceph-csi组件进行 controller端扩容；

（3）ceph-csi组件调用ceph存储，进行底层存储扩容；

（4）底层存储扩容完成后，ceph-csi组件更新pv对象的.Spec.Capacity.storgage的值为扩容后的存储大小；

（5）kubelet的volume manager在reconcile()调谐过程中发现pv.Spec.Capacity.storage大于pvc.Status.Capacity.storage，于是调ceph-csi组件进行 node端扩容；

（6）ceph-csi组件对node上存储对应的文件系统扩容；

（7）扩容完成后，kubelet更新pvc.Status.Capacity.storage的值为扩容后的存储大小。

本节将对controller端存储扩容进行分析，node端存储扩容已经在之前有分析过了，可以看kubelet pvc存储扩容相关代码分析

当pvc.Spec.Resources.Requests大小比pvc.Status.Capacity.storgage大时，会触发到controller端（external-resizer）的扩容逻辑。

controller端（external-resizer）的扩容操作包括：

（1）调用csi plugin的ControllerExpandVolume方法进行存储扩容；

（2）更新pv对象的.spec.capacity.storage为扩容后的存储大小；

（3）更新pvc对象的.Status.Conditions，追加键值对"FileSystemResizePending":"true"，表明该pvc的controller端扩容已经完成，接下来将由kubelet完成node端的存储扩容操作。

源码分析

Run

主要逻辑：根据workers的数量，起数量相等的goroutine不断的跑ctrl.syncPVCs来处理pvc变更事件，筛选出需要扩容的pvc，触发扩容操作。

// pkg/controller/controller.go

// Run starts the controller.
func (ctrl *resizeController) Run(
    workers int, ctx context.Context) {
    defer ctrl.claimQueue.ShutDown()

    klog.Infof("Starting external resizer %s", ctrl.name)
    defer klog.Infof("Shutting down external resizer %s", ctrl.name)

    stopCh := ctx.Done()

    if !cache.WaitForCacheSync(stopCh, ctrl.pvSynced, ctrl.pvcSynced) {
        klog.Errorf("Cannot sync pv/pvc caches")
        return
    }

    for i := 0; i < workers; i++ {
        go wait.Until(ctrl.syncPVCs, 0, stopCh)
    }

    <-stopCh
}

1.syncPVCs

主要逻辑：调用ctrl.syncPVC

// syncPVCs is the main worker.
func (ctrl *resizeController) syncPVCs() {
    key, quit := ctrl.claimQueue.Get()
    if quit {
        return
    }
    defer ctrl.claimQueue.Done(key)

    if err := ctrl.syncPVC(key.(string)); err != nil {
        // Put PVC back to the queue so that we can retry later.
        ctrl.claimQueue.AddRateLimited(key)
    } else {
        ctrl.claimQueue.Forget(key)
    }
}

1.1 syncPVC

处理扩容判断逻辑与执行扩容操作。

主要逻辑：

（1）获取pvc对象；

（2）调用ctrl.pvcNeedResize从pvc对象层面判断是否需要扩容；

（3）获取pv对象；

（4）调用ctrl.pvNeedResize对比pvc与pv对象判断是否需要扩容；

（5）如需扩容，则调用ctrl.resizePVC做扩容操作。

// syncPVC checks if a pvc requests resizing, and execute the resize operation if requested.
func (ctrl *resizeController) syncPVC(key string) error {
    klog.V(4).Infof("Started PVC processing %q", key)

    namespace, name, err := cache.SplitMetaNamespaceKey(key)
    if err != nil {
        klog.Errorf("Split meta namespace key of pvc %s failed: %v", key, err)
        return err
    }

    pvc, err := ctrl.pvcLister.PersistentVolumeClaims(namespace).Get(name)
    if err != nil {
        if k8serrors.IsNotFound(err) {
            klog.V(3).Infof("PVC %s/%s is deleted, no need to process it", namespace, name)
            return nil
        }
        klog.Errorf("Get PVC %s/%s failed: %v", namespace, name, err)
        return err
    }

    if !ctrl.pvcNeedResize(pvc) {
        klog.V(4).Infof("No need to resize PVC %q", util.PVCKey(pvc))
        return nil
    }

    pv, err := ctrl.pvLister.Get(pvc.Spec.VolumeName)
    if err != nil {
        if k8serrors.IsNotFound(err) {
            klog.V(3).Infof("PV %s is deleted, no need to process it", pvc.Spec.VolumeName)
            return nil
        }
        klog.Errorf("Get PV %q of pvc %q failed: %v", pvc.Spec.VolumeName, util.PVCKey(pvc), err)
        return err
    }

    if !ctrl.pvNeedResize(pvc, pv) {
        klog.V(4).Infof("No need to resize PV %q", pv.Name)
        return nil
    }

    return ctrl.resizePVC(pvc, pv)
}

下面先分析下pvcNeedResize与pvNeedResize方法。

pvcNeedResize

当pvc.Status.Phase==Bound而且pvc.Spec.Resources.Requests.storgage大小比pvc.Status.Capacity.storgage大时返回true，说明符合扩容条件。

// pvcNeedResize returns true is a pvc requests a resize operation.
func (ctrl *resizeController) pvcNeedResize(pvc *v1.PersistentVolumeClaim) bool {
    // Only Bound pvc can be expanded.
    if pvc.Status.Phase != v1.ClaimBound {
        return false
    }
    if pvc.Spec.VolumeName == "" {
        return false
    }
    actualSize := pvc.Status.Capacity[v1.ResourceStorage]
    requestSize := pvc.Spec.Resources.Requests[v1.ResourceStorage]
    return requestSize.Cmp(actualSize) > 0
}

pvNeedResize

当pv.Spec.Resources.Requests.storgage大于或者等于pvc.Status.Capacity.storgage，且pvc的.Status.Conditions中有key为"FileSystemResizePending"，值为“true”的键值对，则说明controller端扩容已完成，该方法返回false；相反的，如果pv.Spec.Resources.Requests.storgage小于pvc.Status.Capacity.storgage，则说明controller端未做扩容操作，需要进行扩容操作，返回true。

扩容分为controller端和node端，先进行controller端（external-resizer触发）的扩容，然后再进行node端（kubelet触发）扩容，扩容操作才算完成。

// pvNeedResize returns true if a pv supports and also requests resize.
func (ctrl *resizeController) pvNeedResize(pvc *v1.PersistentVolumeClaim, pv *v1.PersistentVolume) bool {
    if !ctrl.resizer.CanSupport(pv, pvc) {
        klog.V(4).Infof("Resizer %q doesn't support PV %q", ctrl.name, pv.Name)
        return false
    }

    if (pv.Spec.ClaimRef == nil) || (pvc.Namespace != pv.Spec.ClaimRef.Namespace) || (pvc.UID != pv.Spec.ClaimRef.UID) {
        klog.V(4).Infof("persistent volume is not bound to PVC being updated: %s", util.PVCKey(pvc))
        return false
    }

    pvSize := pv.Spec.Capacity[v1.ResourceStorage]
    requestSize := pvc.Spec.Resources.Requests[v1.ResourceStorage]
    if pvSize.Cmp(requestSize) >= 0 {
        // If PV size is equal or bigger than request size, that means we have already resized PV.
        // In this case we need to check PVC's condition.
        // 1. If PVC in PersistentVolumeClaimResizing condition, we should continue to perform the
        //    resizing operation as we need to know if file system resize if required. (What's more,
        //    we hope the driver can find that the actual size already matched the request size and do nothing).
        // 2. If PVC in PersistentVolumeClaimFileSystemResizePending condition, we need to
        //    do nothing as kubelet will finish file system resizing and mark resize as finished.
        if util.HasFileSystemResizePendingCondition(pvc) {
            // This is case 2.
            return false
        }
        // This is case 1.
        return true
    }

    // PV size is smaller than request size, we need to resize the volume.
    return true
}

当controller端扩容已经完成时，util.HasFileSystemResizePendingCondition返回true。主要根据pvc.Status.Conditions中key为"FileSystemResizePending"，值为“true”来判断。

const (
    // PersistentVolumeClaimFileSystemResizePending - controller resize is finished and a file system resize is pending on node
    PersistentVolumeClaimFileSystemResizePending PersistentVolumeClaimConditionType = "FileSystemResizePending"
)

// HasFileSystemResizePendingCondition returns true if a pvc has a FileSystemResizePending condition.
// This means the controller side resize operation is finished, and kublete side operation is in progress.
func HasFileSystemResizePendingCondition(pvc *v1.PersistentVolumeClaim) bool {
    for _, condition := range pvc.Status.Conditions {
        if condition.Type == v1.PersistentVolumeClaimFileSystemResizePending && condition.Status == v1.ConditionTrue {
            return true
        }
    }
    return false
}

1.1.1 resizePVC

该方法负责扩容操作的逻辑。

主要逻辑：

（1）调用ctrl.markPVCResizeInProgress，更新pvc对象的.Status.Conditions，追加键值对"Resizing":"true"，表明该pvc正在进行resize；

（2）调用ctrl.resizeVolume做扩容操作；

（3）扩容完成，调用ctrl.markPVCResizeFinished，更新pvc对象的.Status.Conditions，追加键值对"FileSystemResizePending":"true"，表明该pvc的controller端扩容已经完成。

// resizePVC will:
// 1. Mark pvc as resizing.
// 2. Resize the volume and the pv object.
// 3. Mark pvc as resizing finished(no error, no need to resize fs), need resizing fs or resize failed.
func (ctrl *resizeController) resizePVC(pvc *v1.PersistentVolumeClaim, pv *v1.PersistentVolume) error {
    if updatedPVC, err := ctrl.markPVCResizeInProgress(pvc); err != nil {
        klog.Errorf("Mark pvc %q as resizing failed: %v", util.PVCKey(pvc), err)
        return err
    } else if updatedPVC != nil {
        pvc = updatedPVC
    }

    // Record an event to indicate that external resizer is resizing this volume.
    ctrl.eventRecorder.Event(pvc, v1.EventTypeNormal, util.VolumeResizing,
        fmt.Sprintf("External resizer is resizing volume %s", pv.Name))

    err := func() error {
        newSize, fsResizeRequired, err := ctrl.resizeVolume(pvc, pv)
        if err != nil {
            return err
        }

        if fsResizeRequired {
            // Resize volume succeeded and need to resize file system by kubelet, mark it as file system resizing required.
            return ctrl.markPVCAsFSResizeRequired(pvc)
        }
        // Resize volume succeeded and no need to resize file system by kubelet, mark it as resizing finished.
        return ctrl.markPVCResizeFinished(pvc, newSize)
    }()

    if err != nil {
        // Record an event to indicate that resize operation is failed.
        ctrl.eventRecorder.Eventf(pvc, v1.EventTypeWarning, util.VolumeResizeFailed, err.Error())
    }

    return err
}

resizeVolume

主要逻辑：

（1）调用ctrl.resizer.Resize进行存储扩容；

（2）调用util.UpdatePVCapacity更新pv的.spec.capacity.storage。

// resizeVolume resize the volume to request size, and update PV's capacity if succeeded.
func (ctrl *resizeController) resizeVolume(
    pvc *v1.PersistentVolumeClaim,
    pv *v1.PersistentVolume) (resource.Quantity, bool, error) {
    requestSize := pvc.Spec.Resources.Requests[v1.ResourceStorage]

    newSize, fsResizeRequired, err := ctrl.resizer.Resize(pv, requestSize)

    if err != nil {
        klog.Errorf("Resize volume %q by resizer %q failed: %v", pv.Name, ctrl.name, err)
        return newSize, fsResizeRequired, fmt.Errorf("resize volume %s failed: %v", pv.Name, err)
    }
    klog.V(4).Infof("Resize volume succeeded for volume %q, start to update PV's capacity", pv.Name)

    if err := util.UpdatePVCapacity(pv, newSize, ctrl.kubeClient); err != nil {
        klog.Errorf("Update capacity of PV %q to %s failed: %v", pv.Name, newSize.String(), err)
        return newSize, fsResizeRequired, err
    }
    klog.V(4).Infof("Update capacity of PV %q to %s succeeded", pv.Name, newSize.String())

    return newSize, fsResizeRequired, nil
}

ctrl.resizer.Resize：组装请求，调用r.client.Expand进行存储扩容（实际是调用csi plugin的ControllerExpandVolume方法）

// Resize resizes the persistence volume given request size
// It supports both CSI volume and migrated in-tree volume
func (r *csiResizer) Resize(pv *v1.PersistentVolume, requestSize resource.Quantity) (resource.Quantity, bool, error) {
    oldSize := pv.Spec.Capacity[v1.ResourceStorage]

    var volumeID string
    var source *v1.CSIPersistentVolumeSource
    var pvSpec v1.PersistentVolumeSpec
    if pv.Spec.CSI != nil {
        // handle CSI volume
        source = pv.Spec.CSI
        volumeID = source.VolumeHandle
        pvSpec = pv.Spec
    } else {
        if csitranslationlib.IsMigratedCSIDriverByName(r.name) {
            // handle migrated in-tree volume
            csiPV, err := csitranslationlib.TranslateInTreePVToCSI(pv)
            if err != nil {
                return oldSize, false, fmt.Errorf("failed to translate persistent volume: %v", err)
            }
            source = csiPV.Spec.CSI
            pvSpec = csiPV.Spec
            volumeID = source.VolumeHandle
        } else {
            // non-migrated in-tree volume
            return oldSize, false, fmt.Errorf("volume %v is not migrated to CSI", pv.Name)
        }
    }

    if len(volumeID) == 0 {
        return oldSize, false, errors.New("empty volume handle")
    }

    var secrets map[string]string
    secreRef := source.ControllerExpandSecretRef
    if secreRef != nil {
        var err error
        secrets, err = getCredentials(r.k8sClient, secreRef)
        if err != nil {
            return oldSize, false, err
        }
    }

    secrets[pvCephMountPathKey] = pv.Annotations[pvCephMountPathKey]

    capability, err := GetVolumeCapabilities(pvSpec)
    if err != nil {
        return oldSize, false, fmt.Errorf("failed to get capabilities of volume %s with %v", pv.Name, err)
    }

    ctx, cancel := timeoutCtx(r.timeout)
    defer cancel()
    newSizeBytes, nodeResizeRequired, err := r.client.Expand(ctx, volumeID, requestSize.Value(), secrets, capability)
    if err != nil {
        return oldSize, nodeResizeRequired, err
    }

    return *resource.NewQuantity(newSizeBytes, resource.BinarySI), nodeResizeRequired, err
}



// pkg/csi/client.go
func (c *client) Expand(
    ctx context.Context,
    volumeID string,
    requestBytes int64,
    secrets map[string]string,
    capability *csi.VolumeCapability) (int64, bool, error) {
    req := &csi.ControllerExpandVolumeRequest{
        Secrets:          secrets,
        VolumeId:         volumeID,
        CapacityRange:    &csi.CapacityRange{RequiredBytes: requestBytes},
        VolumeCapability: capability,
    }
    resp, err := c.ctrlClient.ControllerExpandVolume(ctx, req)
    if err != nil {
        return 0, false, err
    }
    return resp.CapacityBytes, resp.NodeExpansionRequired, nil
}

util.UpdatePVCapacity：更新pv对象的.spec.capacity.storage为扩容后的大小。

// UpdatePVCapacity updates PVC capacity with requested size.
func UpdatePVCapacity(pv *v1.PersistentVolume, newCapacity resource.Quantity, kubeClient kubernetes.Interface) error {
    newPV := pv.DeepCopy()
    newPV.Spec.Capacity[v1.ResourceStorage] = newCapacity
    patchBytes, err := getPatchData(pv, newPV)
    if err != nil {
        return fmt.Errorf("can't update capacity of PV %s as generate path data failed: %v", pv.Name, err)
    }
    _, updateErr := kubeClient.CoreV1().PersistentVolumes().Patch(pv.Name, types.StrategicMergePatchType, patchBytes)
    if updateErr != nil {
        return fmt.Errorf("update capacity of PV %s failed: %v", pv.Name, updateErr)
    }
    return nil
}

至此，external-resizer的扩容分析结束。