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.
An Azure disk can only be mounted with Access mode type ReadWriteOnce, which makes it available to one node in AKS. If you need to share a persistent volume across multiple nodes, use Azure Files.
For more information on Kubernetes volumes, see Storage options for applications in AKS.
Before you begin
You also need the Azure CLI version 2.0.59 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 four pre-created storage classes, two of them configured to work with Azure disks:
- The default storage class provisions a standard SSD Azure disk.
- Standard storage is backed by Standard SSDs and delivers cost-effective storage while still delivering reliable performance.
- 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.
If you use one of the default storage classes, you can't update the volume size after the storage class is created. To be able to update the volume size after a storage class is created, add the line
allowVolumeExpansion: true to one of the default storage classes, or you can create you own custom storage class. Note that it's not supported to reduce the size of a PVC (to prevent data loss). You can edit an existing storage class by using the
kubectl edit sc command.
For example, if you want to use a disk of size 4 TiB, you must create a storage class that defines
cachingmode: None because disk caching isn't supported for disks 4 TiB and larger.
For more information about storage classes and creating your own storage class, see Storage options for applications in AKS.
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
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 (in preview). 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
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. For Windows Server containers, specify a mountPath using the Windows path convention, such as 'D:'.
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" [...]
Use Ultra Disks
To leverage ultra disk see Use Ultra Disks on Azure Kubernetes Service (AKS).
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 [...]
For associated best practices, see Best practices for storage and backups in AKS.
Learn more about Kubernetes persistent volumes using Azure disks.