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7.Run-Stateful-Apps-with-disks.MD

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Running Stateful Application on Azure Kubernetes Service (AKS)

Create persistent volumes with Azure disks for 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.

Note

An Azure disk can only be mounted with Access mode type ReadWriteOnce, which makes it available to only a single AKS node. If needing to share a persistent volume across multiple nodes, consider using Azure Files

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][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][kubectl-get] 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 4TiB for S50 or P50 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][managed-disk-pricing-performance].

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. This file is already available in your repo

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 create][kubectl-create] command and specify your azure-premium.yaml file:

$ kubectl create -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. This file is already available in your cloned repo

kind: Pod
apiVersion: v1
metadata:
  name: mypod
spec:
  containers:
    - name: myfrontend
      image: nginx
      volumeMounts:
      - mountPath: "/mnt/azure"
        name: volume
  volumes:
    - name: volume
      persistentVolumeClaim:
        claimName: azure-managed-disk

Create the pod with the [kubectl create][kubectl-create] command, as shown in the following example:

$ kubectl create -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"
[...]