我有一个kubernetes群集，它正在外部网络中运行，并在同一网络中的另一台计算机上设置了一个NFS服务器。我可以通过ssh连接到群集中的任何节点，并通过运行sudo mount -t nfs 10.17.10.190:/export/test /mnt从服务器挂载，但每当我的测试pod尝试使用指向该服务器的nfs持久卷时，它都会失败，并显示以下消息：

Events:
  FirstSeen LastSeen    Count   From            SubObjectPath   Type       Reason       Message
  --------- --------    -----   ----            -------------   --------    ------      -------
  19s       19s     1   default-scheduler           Normal      Scheduled   Successfully assigned nfs-web-58z83 to wal-vm-newt02
  19s       3s      6   kubelet, wal-vm-newt02          Warning     
FailedMount MountVolume.SetUp failed for volume "kubernetes.io/nfs/bad55e9c-7303-11e7-9c2f-005056b40350-test-nfs" (spec.Name: "test-nfs") pod "bad55e9c-7303-11e7-9c2f-005056b40350" (UID: "bad55e9c-7303-11e7-9c2f-005056b40350") with: mount failed: exit status 32
Mounting command: mount
Mounting arguments: 10.17.10.190:/exports/test /var/lib/kubelet/pods/bad55e9c-7303-11e7-9c2f-005056b40350/volumes/kubernetes.io~nfs/test-nfs nfs []
Output: mount.nfs: access denied by server while mounting 10.17.10.190:/exports/test

有人知道我如何修复这个问题，使它可以从外部NFS服务器挂载吗？
群集的节点在10.17.10.185 - 10.17.10.189上运行，所有Pod运行的ip以10.0.x.x开头。群集上的所有节点和NFS服务器运行Ubuntu。NFS服务器在10.17.10.190上运行，/etc/exports为：

/export         10.17.10.185/255.0.0.0(rw,sync,no_subtree_check)

我设置了一个持久卷和持久卷声明，它们都成功创建，显示了运行kubectl get pv,pvc后的输出：

NAME          CAPACITY   ACCESSMODES   RECLAIMPOLICY   STATUS    CLAIM              STORAGECLASS   REASON    AGE
pv/test-nfs   1Mi        RWX           Retain          Bound     staging/test-nfs                            15m

NAME           STATUS    VOLUME     CAPACITY   ACCESSMODES   STORAGECLASS   AGE
pvc/test-nfs   Bound     test-nfs   1Mi        RWX                          15m

它们是这样创建的：

apiVersion: v1
kind: PersistentVolume
metadata:
  name: test-nfs
spec:
  capacity:
    storage: 1Mi
  accessModes:
    - ReadWriteMany
  nfs:
    # FIXME: use the right IP
    server: 10.17.10.190
    path: "/exports/test"
---
kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: test-nfs
spec:
  accessModes:
    - ReadWriteMany
  resources:
    requests:
      storage: 1Mi

我的测试pod正在使用此配置：

apiVersion: v1
kind: ReplicationController
metadata:
  name: nfs-web
spec:
  replicas: 1
  selector:
    role: web-frontend
  template:
    metadata:
      labels:
        role: web-frontend
    spec:
      containers:
      - name: web
        image: nginx
        ports:
          - name: web
            containerPort: 80
        volumeMounts:
            # name must match the volume name below
            - name: test-nfs
              mountPath: "/usr/share/nginx/html"
      volumes:
      - name: test-nfs
        persistentVolumeClaim:
          claimName: test-nfs