Dynamically create and use a persistent volume with Azure disks in Azure Kubernetes Service (AKS)

A persistent volume represents a piece of storage that has been provisioned for use with Kubernetes pods. A persistent volume can be used by one or many pods, and can be dynamically or statically provisioned. This article shows you how to dynamically create persistent volumes with Azure disks for use by a single pod in an Azure Kubernetes Service (AKS) cluster.

Note

An Azure disk can only be mounted with Access mode type ReadWriteOnce, which makes it available to only a single pod in AKS. If you need to share a persistent volume across multiple pods, use Azure Files.

For more information on Kubernetes persistent volumes, see Kubernetes persistent volumes.

Before you begin

This article assumes that you have an existing AKS cluster. If you need an AKS cluster, see the AKS quickstart using the Azure CLI or using the Azure portal.

You also need the Azure CLI version 2.0.46 or later installed and configured. Run az --version to find the version. If you need to install or upgrade, see Install Azure CLI.

Built in storage classes

A storage class is used to define how a unit of storage is dynamically created with a persistent volume. For more information on Kubernetes storage classes, see Kubernetes Storage Classes.

Each AKS cluster includes two pre-created storage classes, both configured to work with Azure disks:

  • The default storage class provisions a standard Azure disk.
    • Standard storage is backed by HDDs, and delivers cost-effective storage while still being performant. Standard disks are ideal for a cost effective dev and test workload.
  • The managed-premium storage class provisions a premium Azure disk.
    • Premium disks are backed by SSD-based high-performance, low-latency disk. Perfect for VMs running production workload. If the AKS nodes in your cluster use premium storage, select the managed-premium class.

Use the kubectl get sc command to see the pre-created storage classes. The following example shows the pre-create storage classes available within an AKS cluster:

$ kubectl get sc

NAME                PROVISIONER                AGE
default (default)   kubernetes.io/azure-disk   1h
managed-premium     kubernetes.io/azure-disk   1h

Note

Persistent volume claims are specified in GiB but Azure managed disks are billed by SKU for a specific size. These SKUs range from 32GiB for S4 or P4 disks to 32TiB for S80 or P80 disks. The throughput and IOPS performance of a Premium managed disk depends on the both the SKU and the instance size of the nodes in the AKS cluster. For more information, see Pricing and Performance of Managed Disks.

Create a persistent volume claim

A persistent volume claim (PVC) is used to automatically provision storage based on a storage class. In this case, a PVC can use one of the pre-created storage classes to create a standard or premium Azure managed disk.

Create a file named azure-premium.yaml, and copy in the following manifest. The claim requests a disk named azure-managed-disk that is 5GB in size with ReadWriteOnce access. The managed-premium storage class is specified as the storage class.

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: azure-managed-disk
spec:
  accessModes:
  - ReadWriteOnce
  storageClassName: managed-premium
  resources:
    requests:
      storage: 5Gi

Tip

To create a disk that uses standard storage, use storageClassName: default rather than managed-premium.

Create the persistent volume claim with the kubectl apply command and specify your azure-premium.yaml file:

$ kubectl apply -f azure-premium.yaml

persistentvolumeclaim/azure-managed-disk created

Use the persistent volume

Once the persistent volume claim has been created and the disk successfully provisioned, a pod can be created with access to the disk. The following manifest creates a basic NGINX pod that uses the persistent volume claim named azure-managed-disk to mount the Azure disk at the path /mnt/azure.

Create a file named azure-pvc-disk.yaml, and copy in the following manifest.

kind: Pod
apiVersion: v1
metadata:
  name: mypod
spec:
  containers:
  - name: mypod
    image: nginx:1.15.5
    resources:
      requests:
        cpu: 100m
        memory: 128Mi
      limits:
        cpu: 250m
        memory: 256Mi
    volumeMounts:
    - mountPath: "/mnt/azure"
      name: volume
  volumes:
    - name: volume
      persistentVolumeClaim:
        claimName: azure-managed-disk

Create the pod with the kubectl apply command, as shown in the following example:

$ kubectl apply -f azure-pvc-disk.yaml

pod/mypod created

You now have a running pod with your Azure disk mounted in the /mnt/azure directory. This configuration can be seen when inspecting your pod via kubectl describe pod mypod, as shown in the following condensed example:

$ kubectl describe pod mypod

[...]
Volumes:
  volume:
    Type:       PersistentVolumeClaim (a reference to a PersistentVolumeClaim in the same namespace)
    ClaimName:  azure-managed-disk
    ReadOnly:   false
  default-token-smm2n:
    Type:        Secret (a volume populated by a Secret)
    SecretName:  default-token-smm2n
    Optional:    false
[...]
Events:
  Type    Reason                 Age   From                               Message
  ----    ------                 ----  ----                               -------
  Normal  Scheduled              2m    default-scheduler                  Successfully assigned mypod to aks-nodepool1-79590246-0
  Normal  SuccessfulMountVolume  2m    kubelet, aks-nodepool1-79590246-0  MountVolume.SetUp succeeded for volume "default-token-smm2n"
  Normal  SuccessfulMountVolume  1m    kubelet, aks-nodepool1-79590246-0  MountVolume.SetUp succeeded for volume "pvc-faf0f176-8b8d-11e8-923b-deb28c58d242"
[...]

Back up a persistent volume

To back up the data in your persistent volume, take a snapshot of the managed disk for the volume. You can then use this snapshot to create a restored disk and attach to pods as a means of restoring the data.

First, get the volume name with the kubectl get pvc command, such as for the PVC named azure-managed-disk:

$ kubectl get pvc azure-managed-disk

NAME                 STATUS    VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS      AGE
azure-managed-disk   Bound     pvc-faf0f176-8b8d-11e8-923b-deb28c58d242   5Gi        RWO            managed-premium   3m

This volume name forms the underlying Azure disk name. Query for the disk ID with az disk list and provide your PVC volume name, as shown in the following example:

$ az disk list --query '[].id | [?contains(@,`pvc-faf0f176-8b8d-11e8-923b-deb28c58d242`)]' -o tsv

/subscriptions/<guid>/resourceGroups/MC_MYRESOURCEGROUP_MYAKSCLUSTER_EASTUS/providers/MicrosoftCompute/disks/kubernetes-dynamic-pvc-faf0f176-8b8d-11e8-923b-deb28c58d242

Use the disk ID to create a snapshot disk with az snapshot create. The following example creates a snapshot named pvcSnapshot in the same resource group as the AKS cluster (MC_myResourceGroup_myAKSCluster_eastus). You may encounter permission issues if you create snapshots and restore disks in resource groups that the AKS cluster does not have access to.

$ az snapshot create \
    --resource-group MC_myResourceGroup_myAKSCluster_eastus \
    --name pvcSnapshot \
    --source /subscriptions/<guid>/resourceGroups/MC_myResourceGroup_myAKSCluster_eastus/providers/MicrosoftCompute/disks/kubernetes-dynamic-pvc-faf0f176-8b8d-11e8-923b-deb28c58d242

Depending on the amount of data on your disk, it may take a few minutes to create the snapshot.

Restore and use a snapshot

To restore the disk and use it with a Kubernetes pod, use the snapshot as a source when you create a disk with az disk create. This operation preserves the original resource if you then need to access the original data snapshot. The following example creates a disk named pvcRestored from the snapshot named pvcSnapshot:

az disk create --resource-group MC_myResourceGroup_myAKSCluster_eastus --name pvcRestored --source pvcSnapshot

To use the restored disk with a pod, specify the ID of the disk in the manifest. Get the disk ID with the az disk show command. The following example gets the disk ID for pvcRestored created in the previous step:

az disk show --resource-group MC_myResourceGroup_myAKSCluster_eastus --name pvcRestored --query id -o tsv

Create a pod manifest named azure-restored.yaml and specify the disk URI obtained in the previous step. The following example creates a basic NGINX web server, with the restored disk mounted as a volume at /mnt/azure:

kind: Pod
apiVersion: v1
metadata:
  name: mypodrestored
spec:
  containers:
  - name: mypodrestored
    image: nginx:1.15.5
    resources:
      requests:
        cpu: 100m
        memory: 128Mi
      limits:
        cpu: 250m
        memory: 256Mi
    volumeMounts:
    - mountPath: "/mnt/azure"
      name: volume
  volumes:
    - name: volume
      azureDisk:
        kind: Managed
        diskName: pvcRestored
        diskURI: /subscriptions/<guid>/resourceGroups/MC_myResourceGroupAKS_myAKSCluster_eastus/providers/Microsoft.Compute/disks/pvcRestored

Create the pod with the kubectl apply command, as shown in the following example:

$ kubectl apply -f azure-restored.yaml

pod/mypodrestored created

You can use kubectl describe pod mypodrestored to view details of the pod, such as the following condensed example that shows the volume information:

$ kubectl describe pod mypodrestored

[...]
Volumes:
  volume:
    Type:         AzureDisk (an Azure Data Disk mount on the host and bind mount to the pod)
    DiskName:     pvcRestored
    DiskURI:      /subscriptions/19da35d3-9a1a-4f3b-9b9c-3c56ef409565/resourceGroups/MC_myResourceGroupAKS_myAKSCluster_eastus/providers/Microsoft.Compute/disks/pvcRestored
    Kind:         Managed
    FSType:       ext4
    CachingMode:  ReadWrite
    ReadOnly:     false
[...]

Next steps

Learn more about Kubernetes persistent volumes using Azure disks.