Kubernetes Storage Operations

Internal

• Kubernetes Operations
• Kubernetes Storage Concepts

Get Information about Persistent Volumes

kubectl get pv <pv-name>
kubectl describe pv <pv-name>

Get Information about Persistent Volumes Claims

kubectl get pvc <pvc-name>
kubectl describe pvc <pvc-name>

NFS volume Example

This is an example to setup and use an nfs volume.

TODO: https://github.com/kubernetes/examples/tree/master/staging/volumes/nfs

Local Volumes

Create a Local Volume, the corresponding Persistent Volume and a Persistent Volume Claim that Binds to It

This is the step-by-step procedure to create a persistent volume backed by a local volume and expose it to a pod with a matching persistent volume claim.

Expose a Local Disk

In this context, "exposing a local disk" means exposing a raw block device. TODO.

Expose a Local Directory

Define a local directory that will be exposed as a persistent volume:

mkdir /mnt/disk1/local-volume-0

Define the persistent volume API resource instance:

apiVersion: v1
kind: PersistentVolume
metadata:
  name: worker-00-local-volume-0
spec:
  capacity:
    storage: 10Gi
  volumeMode: Filesystem
  accessModes:
  - ReadWriteOnce
  persistentVolumeReclaimPolicy: Delete
  storageClassName: manual-local-storage
  local:
    path: /mnt/disk1/local-volume-0
  nodeAffinity:
    required:
      nodeSelectorTerms:
      - matchExpressions:
        - key: kubernetes.io/hostname
          operator: In
          values:
          - worker-00

Note that in the persistent volume metadata shown above, "worker-00" is the name of the node, as known to Kubernetes. It can be obtained with:

kubectl get nodes -o wide

If the cluster has more than one node, symmetrical persistent volumes can be created for other nodes as well.

Upon creation, the persistent volumes can be listed with:

kubectl get pv
NAME                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS      CLAIM   STORAGECLASS           REASON   AGE
worker-00-local-volume-0   10Gi       RWO            Delete           Available           manual-local-storage            94s
worker-01-local-volume-0   10Gi       RWO            Delete           Available           manual-local-storage            2s

Create a Matching Persistent Volume Claim

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: local-storage-claim
spec:
  accessModes:
  - ReadWriteOnce
  storageClassName: manual-local-storage
  resources:
    requests:
      storage: 10Gi

Aside from attributes like storage amount request access mode, the storage class name must match.

The claim is immediately bound, as it finds a matching persistent volume:

kubectl get pvc
NAME                  STATUS   VOLUME                     CAPACITY   ACCESS MODES   STORAGECLASS           AGE
local-storage-claim   Bound    worker-00-local-volume-0   10Gi       RWO            manual-local-storage   2m19s

kubectl get pv
NAME                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS      CLAIM                         STORAGECLASS           REASON   AGE
worker-00-local-volume-0   10Gi       RWO            Delete           Bound       default/local-storage-claim   manual-local-storage            6m37s
worker-01-local-volume-0   10Gi       RWO            Delete           Available                                 manual-local-storage            5m5s

The pod gets access to the volume content by declaring a persistentVolumeClaim volume:

apiVersion: v1
kind: Pod
metadata:
  name: test
spec:
  containers:
    - name: test
      ...
      volumeMounts:
      - mountPath: "/something"
        name: local-storage
  volumes:
    - name: local-storage
      persistentVolumeClaim:
        claimName: local-storage-claim