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The Azure Files Container Storage Interface (CSI) driver is a CSI specification -compliant driver used by Azure Kubernetes Service (AKS) to manage the lifecycle of Azure file shares. The CSI is a standard for exposing arbitrary block and file storage systems to containerized workloads on Kubernetes.

By adopting and using CSI, AKS now can write, deploy, and iterate plug-ins to expose new or improve existing storage systems in Kubernetes. Using CSI drivers in AKS avoids having to touch the core Kubernetes code and wait for its release cycles.

To create an AKS cluster with CSI drivers support, see Enable CSI drivers on AKS .

In-tree drivers refers to the current storage drivers that are part of the core Kubernetes code versus the new CSI drivers, which are plug-ins.

Azure Files CSI driver new features

In addition to the original in-tree driver features, Azure Files CSI driver supports the following new features:

Use a persistent volume with Azure Files

A persistent volume (PV) represents a piece of storage that's provisioned for use with Kubernetes pods. A PV can be used by one or many pods and can be dynamically or statically provisioned. If multiple pods need concurrent access to the same storage volume, you can use Azure Files to connect by using the Server Message Block (SMB) or NFS protocol . This article shows you how to dynamically create an Azure Files share for use by multiple pods in an AKS cluster. For static provisioning, see Manually create and use a volume with an Azure Files share .

With Azure Files shares, there is no limit as to how many can be mounted on a node.

For more information on Kubernetes volumes, see Storage options for applications in AKS .

Dynamically create Azure Files PVs by using the built-in storage classes

A storage class is used to define how an Azure file share is created. A storage account is automatically created in the node resource group for use with the storage class to hold the Azure files share. Choose one of the following Azure storage redundancy SKUs for skuName :

Azure Files supports Azure Premium Storage. The minimum premium file share capacity is 100 GiB.

When you use storage CSI drivers on AKS, there are two more built-in StorageClasses that uses the Azure Files CSI storage drivers. The other CSI storage classes are created with the cluster alongside the in-tree default storage classes.

The reclaim policy on both storage classes ensures that the underlying Azure files share is deleted when the respective PV is deleted. The storage classes also configure the file shares to be expandable, you just need to edit the persistent volume claim (PVC) with the new size.

To use these storage classes, create a PVC and respective pod that references and uses them. A PVC is used to automatically provision storage based on a storage class. A PVC can use one of the pre-created storage classes or a user-defined storage class to create an Azure files share for the desired SKU and size. When you create a pod definition, the PVC is specified to request the desired storage.

Create an example PVC and pod that prints the current date into an outfile by running the [kubectl apply][kubectl-apply] commands:

kubectl apply -f https://raw.githubusercontent.com/kubernetes-sigs/azurefile-csi-driver/master/deploy/example/pvc-azurefile-csi.yaml
kubectl apply -f https://raw.githubusercontent.com/kubernetes-sigs/azurefile-csi-driver/master/deploy/example/nginx-pod-azurefile.yaml
The output of the command resembles the following example:
persistentvolumeclaim/pvc-azurefile created
pod/nginx-azurefile created
After the pod is in the running state, you can validate that the file share is correctly mounted by running the following command and verifying the output contains the outfile:
kubectl exec nginx-azurefile -- ls -l /mnt/azurefile
The output of the command resembles the following example:
total 29
-rwxrwxrwx 1 root root 29348 Aug 31 21:59 outfile
Create a custom storage class
The default storage classes suit the most common scenarios, but not all. For some cases, you might want to have your own storage class customized with your own parameters. For example, use the following manifest to configure the mountOptions of the file share.
The default value for fileMode and dirMode is 0777 for Kubernetes mounted file shares. You can specify the different mount options on the storage class object.
Create a file named azure-file-sc.yaml, and paste the following example manifest:
kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: my-azurefile
provisioner: file.csi.azure.com
reclaimPolicy: Delete
volumeBindingMode: Immediate
allowVolumeExpansion: true
mountOptions:
  - dir_mode=0640
  - file_mode=0640
  - uid=0
  - gid=0
  - mfsymlinks
  - cache=strict # https://linux.die.net/man/8/mount.cifs
  - nosharesock
parameters:
  skuName: Standard_LRS
Create the storage class by running the [kubectl apply][kubectl-apply] command:
kubectl apply -f azure-file-sc.yaml
The output of the command resembles the following example:
storageclass.storage.k8s.io/my-azurefile created
The Azure Files CSI driver supports creating snapshots of persistent volumes and the underlying file shares.
This driver only supports snapshot creation, restore from snapshot is not supported by this driver. Snapshots can be restored from Azure portal or CLI. For more information about creating and restoring a snapshot, see Overview of share snapshots for Azure Files.
Create a volume snapshot class with the [kubectl apply][kubectl-apply] command:
kubectl apply -f https://raw.githubusercontent.com/kubernetes-sigs/azurefile-csi-driver/master/deploy/example/snapshot/volumesnapshotclass-azurefile.yaml
The output of the command resembles the following example:
volumesnapshotclass.snapshot.storage.k8s.io/csi-azurefile-vsc created
Create a volume snapshot from the PVC we dynamically created at the beginning of this tutorial, pvc-azurefile.
kubectl apply -f https://raw.githubusercontent.com/kubernetes-sigs/azurefile-csi-driver/master/deploy/example/snapshot/volumesnapshot-azurefile.yaml
The output of the command resembles the following example:
volumesnapshot.snapshot.storage.k8s.io/azurefile-volume-snapshot created
Verify the snapshot was created correctly by running the following command:
kubectl describe volumesnapshot azurefile-volume-snapshot
The output of the command resembles the following example:
Name:         azurefile-volume-snapshot
Namespace:    default
Labels:       <none>
Annotations:  API Version:  snapshot.storage.k8s.io/v1beta1
Kind:         VolumeSnapshot
Metadata:
  Creation Timestamp:  2020-08-27T22:37:41Z
  Finalizers:
    snapshot.storage.kubernetes.io/volumesnapshot-as-source-protection
    snapshot.storage.kubernetes.io/volumesnapshot-bound-protection
  Generation:        1
  Resource Version:  955091
  Self Link:         /apis/snapshot.storage.k8s.io/v1beta1/namespaces/default/volumesnapshots/azurefile-volume-snapshot
  UID:               c359a38f-35c1-4fb1-9da9-2c06d35ca0f4
Spec:
  Source:
    Persistent Volume Claim Name:  pvc-azurefile
  Volume Snapshot Class Name:      csi-azurefile-vsc
Status:
  Bound Volume Snapshot Content Name:  snapcontent-c359a38f-35c1-4fb1-9da9-2c06d35ca0f4
  Ready To Use:                        false
Events:                                <none>
Resize a persistent volume
You can request a larger volume for a PVC. Edit the PVC object, and specify a larger size. This change triggers the expansion of the underlying volume that backs the PV.
A new PV is never created to satisfy the claim. Instead, an existing volume is resized.
In AKS, the built-in azurefile-csi storage class already supports expansion, so use the PVC created earlier with this storage class. The PVC requested a 100 GiB file share. We can confirm that by running:
kubectl exec -it nginx-azurefile -- df -h /mnt/azurefile
The output of the command resembles the following example:
Filesystem                                                                                Size  Used Avail Use% Mounted on
//f149b5a219bd34caeb07de9.file.core.windows.net/pvc-5e5d9980-da38-492b-8581-17e3cad01770  100G  128K  100G   1% /mnt/azurefile
Expand the PVC by increasing the spec.resources.requests.storage field:
kubectl patch pvc pvc-azurefile --type merge --patch '{"spec": {"resources": {"requests": {"storage": "200Gi"}}}}'
The output of the command resembles the following example:
persistentvolumeclaim/pvc-azurefile patched
Verify that both the PVC and the file system inside the pod show the new size:
kubectl get pvc pvc-azurefile
NAME            STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS    AGE
pvc-azurefile   Bound    pvc-5e5d9980-da38-492b-8581-17e3cad01770   200Gi      RWX            azurefile-csi   64m
kubectl exec -it nginx-azurefile -- df -h /mnt/azurefile
Filesystem                                                                                Size  Used Avail Use% Mounted on
//f149b5a219bd34caeb07de9.file.core.windows.net/pvc-5e5d9980-da38-492b-8581-17e3cad01770  200G  128K  200G   1% /mnt/azurefile
Use a persistent volume with private Azure Files storage (private endpoint)
If your Azure Files resources are protected with a private endpoint, you must create your own storage class. Make sure that you've configured your DNS settings to resolve the private endpoint IP address to the FQDN of the connection string. Customize the following parameters:
resourceGroup: The resource group where the storage account is deployed.
storageAccount: The storage account name.
server: The FQDN of the storage account's private endpoint.
Create a file named private-azure-file-sc.yaml, and then paste the following example manifest in the file. Replace the values for <resourceGroup> and <storageAccountName>.
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: private-azurefile-csi
provisioner: file.csi.azure.com
allowVolumeExpansion: true
parameters:
  resourceGroup: <resourceGroup>
  storageAccount: <storageAccountName>
  server: <storageAccountName>.file.core.windows.net 
reclaimPolicy: Delete
volumeBindingMode: Immediate
mountOptions:
  - dir_mode=0777
  - file_mode=0777
  - uid=0
  - gid=0
  - mfsymlinks
  - cache=strict  # https://linux.die.net/man/8/mount.cifs
  - nosharesock  # reduce probability of reconnect race
  - actimeo=30  # reduce latency for metadata-heavy workload
Create the storage class by using the kubectl apply command:
kubectl apply -f private-azure-file-sc.yaml
The output of the command resembles the following example:
storageclass.storage.k8s.io/private-azurefile-csi created
Create a file named private-pvc.yaml, and then paste the following example manifest in the file:
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: private-azurefile-pvc
spec:
  accessModes:
    - ReadWriteMany
  storageClassName: private-azurefile-csi
  resources:
    requests:
      storage: 100Gi
Create the PVC by using the [kubectl apply][kubectl-apply] command:
kubectl apply -f private-pvc.yaml
NFS file shares
Azure Files supports the NFS v4.1 protocol. NFS version 4.1 support for Azure Files provides you with a fully managed NFS file system as a service built on a highly available and highly durable distributed resilient storage platform.
This option is optimized for random access workloads with in-place data updates and provides full POSIX file system support. This section shows you how to use NFS shares with the Azure File CSI driver on an AKS cluster.
Prerequisites
Your AKS cluster Control plane identity (that is, your AKS cluster name) is added to the Contributor role on the VNet and NetworkSecurityGroup.
Your AKS cluster's service principal or managed service identity (MSI) must be added to the Contributor role to the storage account.
You can use a private endpoint instead of allowing access to the selected VNet.
Create NFS file share storage class
Create a file named nfs-sc.yaml and copy the manifest below.
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: azurefile-csi-nfs
provisioner: file.csi.azure.com
allowVolumeExpansion: true
parameters:
  protocol: nfs
mountOptions:
  - nconnect=4
After editing and saving the file, create the storage class with the [kubectl apply][kubectl-apply] command:
kubectl apply -f nfs-sc.yaml
The output of the command resembles the following example:
storageclass.storage.k8s.io/azurefile-csi-nfs created
Create a deployment with an NFS-backed file share
You can deploy an example stateful set that saves timestamps into a file data.txt with the [kubectl apply][kubectl-apply] command:
kubectl apply -f
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: statefulset-azurefile
  labels:
    app: nginx
spec:
  podManagementPolicy: Parallel  # default is OrderedReady
  serviceName: statefulset-azurefile
  replicas: 1
  template:
    metadata:
      labels:
        app: nginx
    spec:
      nodeSelector:
        "kubernetes.io/os": linux
      containers:
        - name: statefulset-azurefile
          image: mcr.microsoft.com/oss/nginx/nginx:1.19.5
          command:
            - "/bin/bash"
            - "-c"
            - set -euo pipefail; while true; do echo $(date) >> /mnt/azurefile/outfile; sleep 1; done
          volumeMounts:
            - name: persistent-storage
              mountPath: /mnt/azurefile
  updateStrategy:
    type: RollingUpdate
  selector:
    matchLabels:
      app: nginx
  volumeClaimTemplates:
    - metadata:
        name: persistent-storage
      spec:
        storageClassName: azurefile-csi-nfs
        accessModes: ["ReadWriteMany"]
        resources:
          requests:
            storage: 100Gi
The output of the command resembles the following example:
statefulset.apps/statefulset-azurefile created
Validate the contents of the volume by running the following command:
kubectl exec -it statefulset-azurefile-0 -- df -h
The output of the command resembles the following example:
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1                                                                                 29G   11G   19G  37% /etc/hosts
accountname.file.core.windows.net:/accountname/pvc-fa72ec43-ae64-42e4-a8a2-556606f5da38  100G     0  100G   0% /mnt/azurefile
Note that because the NFS file share is in a Premium account, the minimum file share size is 100 GiB. If you create a PVC with a small storage size, you might encounter an error similar to the following: failed to create file share ... size (5)....
Windows containers
The Azure Files CSI driver also supports Windows nodes and containers. To use Windows containers, follow the Windows containers quickstart to add a Windows node pool.
After you have a Windows node pool, use the built-in storage classes like azurefile-csi or create a custom one. You can deploy an example Windows-based stateful set that saves timestamps into a file data.txt by running the [kubectl apply][kubectl-apply] command:
kubectl apply -f https://raw.githubusercontent.com/kubernetes-sigs/azurefile-csi-driver/master/deploy/example/windows/statefulset.yaml
The output of the command resembles the following example:
statefulset.apps/busybox-azurefile created
Validate the contents of the volume by running the following kubectl exec command:
kubectl exec -it busybox-azurefile-0 -- cat c:\\mnt\\azurefile\\data.txt # on Linux/MacOS Bash
kubectl exec -it busybox-azurefile-0 -- cat c:\mnt\azurefile\data.txt # on Windows Powershell/CMD
The output of the commands resembles the following example:
2020-08-27 22:11:01Z
2020-08-27 22:11:02Z
2020-08-27 22:11:04Z
(...)
Next steps
To learn how to use CSI driver for Azure Disks, see Use Azure Disks with CSI driver.
To learn how to use CSI driver for Azure Blob storage, see Use Azure Blob storage with CSI driver.
For more about storage best practices, see Best practices for storage and backups in Azure Kubernetes Service.