Using NFS Storage

Users can provide persistent storage for workloads running on MKE by using NFS storage. These NFS shares, when mounted into the running container, provide state to the application, managing data external to the container’s lifecycle.

Note

Provisioning an NFS server and exporting an NFS share are out of scope for this guide. Additionally, using external Kubernetes plugins to dynamically provision NFS shares is also out of scope for this guide.

There are two options to mount existing NFS shares within Kubernetes Pods:

  • Define NFS shares within the Pod definitions. NFS shares are defined manually by each tenant when creating a workload.

  • Define NFS shares as a Cluster object through Persistent Volumes, with the Cluster object lifecycle handled separately from the workload. This is common for operators who want to define a range of NFS shares for tenants to request and consume.

Defining NFS Shares in the Pod definition

When defining workloads in Kubernetes manifest files, an end user can directly reference the NFS shares to mount inside of each Pod. The NFS share is defined within the Pod specification, which could be a standalone pod, or could be wrapped in a higher-level object like a Deployment, Daemonset, or StatefulSet.

The following example includes a running MKE cluster and a downloaded client bundle with permission to schedule pods in a namespace.

Example pod specification with an NFS volume defined

$ cat nfs-in-a-pod.yaml
kind: Pod
apiVersion: v1
metadata:
  name: nfs-in-a-pod
spec:
  containers:
    - name: app
      image: alpine
      volumeMounts:
        - name: nfs-volume
          mountPath: /var/nfs
         # Please change the destination you like the share to be mounted too
      command: ["/bin/sh"]
      args: ["-c", "sleep 500000"]
  volumes:
    - name: nfs-volume
      nfs:
        server: nfs.example.com # Please change this to your NFS server
        path: /share1 # Please change this to the relevant share

To deploy the pod, and ensure that it started up correctly, use the kubectl command line tool.

$ kubectl create -f nfsinapod.yaml

$ kubectl get pods
NAME                     READY     STATUS      RESTARTS   AGE
nfs-in-a-pod             1/1       Running     0          6m

Verify everything was mounted correctly by getting a shell prompt within the container and searching for your mount.

$ kubectl exec -it nfs-in-a-pod sh
/ #
/ # mount | grep nfs.example.com
nfs.example.com://share1 on /var/nfs type nfs4 (rw,relatime,vers=4.0,rsize=262144,wsize=262144,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=172.31.42.23,local_lock=none,addr=nfs.example.com)
/ #

Because you defined the NFS share as part of the Pod spec, neither MKE nor Kubernetes knows anything about this NFS share. This means that when the pod gets deleted, the NFS share is unattached from the Cluster. However, the data remains in the NFS share.

Exposing NFS shares as a Cluster Object

For this method, use the Kubernetes Objects PV and PVC to manage the lifecycle and access to NFS Shares.

You can define multiple shares for a tenant to use within the cluster. The PV is a cluster wide object, so it can be pre-provisioned. A PVC is a claim by a tenant for use of a PV within their namespace.

Note

In this case, ‘NFS share lifecycle’ refers to granting and removing the end user’s ability to consume NFS storage, not managing the lifecycle of the NFS Server.

Persistent Volume

Define the PV at the cluster level.

$ cat pvwithnfs.yaml
apiVersion: v1
kind: PersistentVolume
metadata:
  name: my-nfs-share
spec:
  capacity:
    storage: 5Gi
    # This size is used to match a volume to a tenents claim
  accessModes:
    - ReadWriteOnce
    # Access modes are defined below
  persistentVolumeReclaimPolicy: Recycle
  # Reclaim policies are defined below
  nfs:
    server: nfs.example.com
    # Please change this to your NFS server
    path: /share1 # Please change this to the relevant share

To create PPV objects at the Cluster level, you need a Cluster Role Binding grant. Use the kubectl command line tool to create the volume:

$ kubectl create -f pvwithnfs.yaml

$ kubectl get pv
NAME           CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS      CLAIM                       STORAGECLASS   REASON    AGE

my-nfs-share   5Gi        RWO            Recycle          Available                               slow                     7s

Access Modes

The access mode for a NFS PV can be any of the following modes:

  • ReadWriteOnce – the volume can be mounted as read-write by a single node.

  • ReadOnlyMany – the volume can be mounted read-only by many nodes.

  • ReadWriteMany – the volume can be mounted as read-write by many nodes.

The access mode in the PV definition is used to match a PV to a Claim. When a PV is defined and created inside of Kubernetes, a Volume is not mounted. See access modes for more details.

Reclaim

The reclaim policy is used to define what the cluster should do after a PV has been released from a Claim. A PV Reclaim policy could be: Reclaim, Recycle, and Delete. See Reclaiming for more information.

Persistent Volume Claim

A tenant can now “claim” a PV for use within their workloads by using a Kubernetes PVC. A PVC resides within a namespace, and it attempts to match available PVs to what a tenant has requested.

$ cat myapp-claim.yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: myapp-nfs
  namespace: default
spec:
  accessModes:
    - ReadWriteOnce
    # Access modes for volumes is defined under Persistent Volumes
  resources:
    requests:
      storage: 5Gi # volume size requested

A tenant with a RoleBinding to create PVCs can deploy this PVC. If there is a PV that meets the tenant’s criteria, Kubernetes binds the PV to the Claim. Again, this does not mount the share.

$ kubectl create -f myapp-claim.yaml
persistentvolumeclaim "myapp-nfs" created

$ kubectl get pvc
NAME        STATUS    VOLUME         CAPACITY   ACCESS MODES   STORAGECLASS   AGE
myapp-nfs   Bound     my-nfs-share   5Gi        RWO            slow           2s

$ kubectl get pv
NAME           CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS    CLAIM              STORAGECLASS   REASON    AGE
my-nfs-share   5Gi        RWO            Recycle          Bound     default/myapp-nfs  slow                     4m

Defining a workload

Finally, a tenant can deploy a workload to consume the PVC. The PVC is defined within the Pod specification, which could be a standalone pod or could be wrapped in a higher-level object like a Deployment, Daemonset, or StatefulSet.

$ cat myapp-pod.yaml
kind: Pod
apiVersion: v1
metadata:
  name: pod-using-nfs
spec:
  containers:
    - name: app
      image: alpine
      volumeMounts:
      - name: data
          mountPath: /var/nfs
          # Please change the destination you like the share to be mounted too
      command: ["/bin/sh"]
      args: ["-c", "sleep 500000"]
  volumes:
  - name: data
    persistentVolumeClaim:
      claimName: myapp-nfs

The pod can be deployed by a tenant using the kubectl command line tool. Additionally, you can verify that the pod is running successfully and that the NFS share has been mounted inside of the container.

$ kubectl create -f myapp-pod.yaml

$ kubectl get pod
NAME                     READY     STATUS      RESTARTS   AGE
pod-using-nfs            1/1       Running     0          1m

$ kubectl exec -it pod-using-nfs sh
/ # mount | grep nfs.example.com
nfs.example.com://share1 on /var/nfs type nfs4 (rw,relatime,vers=4.1,rsize=262144,wsize=262144,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=172.31.42.23,local_lock=none,addr=nfs.example.com)
/ #