:Automatically scale out NAS volumes using CNFS

How it works

The auto-scaling workflow is handled entirely by the storage-operator component.

1. Define a policy. Create a StorageAutoScalerPolicy resource that specifies the target PersistentVolumeClaim (PVC), trigger conditions, and scale-out actions.

   The StorageClass used by the PVC must have allowVolumeExpansion: true.

2. Monitor continuously. The storage-operator monitors real-time storage usage of the target PVC.

3. Trigger scale-out. When conditions are met, the storage-operator sends a scale-out request to the PVC.

4. Execute scale-out. The Container Storage Interface (CSI) driver processes the request, and Alibaba Cloud NAS performs the actual file system expansion.

5. Synchronize status. The PVC status updates automatically to reflect the new capacity.

Prerequisites

Before you begin, ensure that you have:

• csi-plugin and csi-provisioner at version v1.20.5-ff6490f-aliyun or later. To upgrade, see Upgrade CSI components.

• storage-operator at version v1.18.8.56-2aa33ba-aliyun or later. To upgrade, see Manage the storage-operator component.

• cnfs-controller installed. This is a managed component installed by default — verify it has not been uninstalled.

• A CNFS with Available status. To create one, see Manage NAS file systems with CNFS.

For storage-operator versions earlier than v1.33.1: Run the following command to enable the auto-scaling feature in the ConfigMap before proceeding:

kubectl patch configmap/storage-operator \
  -n kube-system \
  --type merge \
  -p '{"data":{"storage-auto-expander":"{\"imageRep\":\"acs/storage-auto-expander\",\"imageTag\":\"\",\"install\":\"true\",\"template\":\"/acs/templates/storage-auto-expander/install.yaml\",\"type\":\"deployment\"}"}}'

To verify CNFS status:

# List all CNFS objects
kubectl get cnfs

# Check the status of a specific CNFS
kubectl get cnfs <CNFS_NAME> -o yaml | grep Available

Expected output:

NAME                                      AGE
default-cnfs-nas-837d6ea-20210819155623   14d

status: Available

Step 1: Define the scale-out policy

Create a StorageAutoScalerPolicy resource to specify when and how the storage-operator expands your NAS volume.

The following example triggers a scale-out when capacity usage of a PVC labeled app: nginx (in the default or nginx namespace) exceeds 80%. Each expansion doubles the current capacity, up to a maximum of 200 GiB.

cat << EOF | kubectl apply -f -
apiVersion: storage.alibabacloud.com/v1alpha1
kind: StorageAutoScalerPolicy
metadata:
  name: hybrid-expand-policy
spec:
  # Match PVCs by label selector.
  pvcSelector:
    matchLabels:
      app: nginx  # Must match the labels on your PVC and Deployment.
  # Namespaces where this policy applies.
  namespaces:
    - default
    - nginx
  # Conditions that trigger a scale-out.
  conditions:
    - name: condition1
      key: volume-capacity-used-percentage  # Metric: capacity usage percentage.
      operator: Gt                          # Greater than.
      values:
        - "80"                              # Threshold: 80%.
  # Actions to perform when conditions are met.
  actions:
    - name: action1
      type: volume-expand
      params:
        scale: 100%    # Increase capacity by 100% of the current size.
        limits: 200Gi  # Cap total capacity at 200 GiB.
EOF

Policy parameters:

conditions parameters:

actions parameters:

Step 2: Create a StorageClass

Create a StorageClass that references your existing CNFS NAS file system. Set allowVolumeExpansion: true — this establishes the capacity baseline that the auto-scaling policy uses to calculate usage.

cat << EOF | kubectl apply -f -
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: alibabacloud-cnfs-nas  # Referenced in the PVC in the next step.
mountOptions:
- nolock,tcp,noresvport
- vers=3
parameters:
  volumeAs: subpath
  # Format: <nas-server-address>:/<path>
  server: "0cd8b4a576-g****.cn-hangzhou.nas.aliyuncs.com:/k8s"
  archiveOnDelete: "true"
provisioner: nasplugin.csi.alibabacloud.com
reclaimPolicy: Retain
allowVolumeExpansion: true  # Required for auto-scaling.
EOF

For a full list of StorageClass parameters, see Manage NAS file systems with CNFS.

Step 3: Deploy the application and PVC

Create a PVC and a Deployment with labels that match the pvcSelector.matchLabels in your policy (app: nginx). The storage-operator uses these labels to associate the policy with the correct PVC.

cat << EOF | kubectl apply -f -
kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: cnfs-nas-pvc
  labels:
    app: nginx  # Must match pvcSelector.matchLabels in the policy.
spec:
  accessModes:
    - ReadWriteMany
  storageClassName: alibabacloud-cnfs-nas  # References the StorageClass created earlier.
  resources:
    requests:
      storage: 20Gi
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: cnfs-nas-deployment
  labels:
    app: nginx
spec:
  selector:
    matchLabels:
      app: nginx  # Must match pvcSelector.matchLabels in the policy.
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: anolis-registry.cn-zhangjiakou.cr.aliyuncs.com/openanolis/nginx:1.14.1-8.6
        volumeMounts:
        - mountPath: "/data"
          name: cnfs-nas-pvc
      volumes:
      - name: cnfs-nas-pvc
        persistentVolumeClaim:
          claimName: cnfs-nas-pvc
EOF

Step 4: Verify auto-scaling

Trigger a scale-out by writing test data, then confirm the expansion through events and the monitoring dashboard.

1. Confirm the Pod is running.

   kubectl get pods -l app=nginx

   Expected output:

   NAME                                       READY   STATUS    RESTARTS   AGE
   cnfs-nas-deployment-56dbcc7fb7-wh79z       1/1     Running   0          20m

2. Record the initial PVC capacity before writing any data.

   kubectl get pvc cnfs-nas-pvc

   Expected output (initial state, 20 GiB):

   NAME           STATUS   VOLUME       CAPACITY   ACCESS MODES   STORAGECLASS             AGE
   cnfs-nas-pvc   Bound    ...          20Gi       RWX            alibabacloud-cnfs-nas    2m

3. Write 20 GiB of test data to push usage above the 80% threshold.

   The write operation may take several minutes depending on network throughput and storage performance.

   kubectl exec -it <POD_NAME> -- dd if=/dev/zero of=/data/testfile bs=1G count=20

4. Check the events generated by the scale-out.

   kubectl get events | grep cnfs-nas-pvc

   The StartExpand and VolumeResizeSuccessful events confirm the expansion completed. In this example, the PVC scaled from 20 GiB to 40 GiB (100% increase).

   12s   Warning  StartExpand            persistentvolumeclaim/cnfs-nas-pvc   Start to expand of pvc cnfs-nas-pvc from 20Gi to 40Gi, usedCapacityPercentage:99%, freeSize:204MB.
   12s   Normal   ExternalExpanding      persistentvolumeclaim/cnfs-nas-pvc   waiting for an external controller to expand this PVC
   12s   Normal   Resizing               persistentvolumeclaim/cnfs-nas-pvc   External resizer is resizing volume nas-462db2b2-717d-44fe-b0b6-fb4db03a****
   12s   Normal   VolumeResizeSuccessful persistentvolumeclaim/cnfs-nas-pvc   Resize volume succeeded

   Confirm the updated capacity:

   kubectl get pvc cnfs-nas-pvc

5. (Optional) View the usage trend on the CSI NAS monitoring dashboard. In this example, the scale-out was triggered at 10:23:30, and the capacity after expansion is 100 GiB.

   Requires Alibaba Cloud Prometheus Monitoring.

   1. On the Clusters page, click your cluster name. In the left navigation pane, choose Operations > Prometheus Monitoring.

   2. Click the Storage Monitoring tab, then click CSI NAS.

   3. Set Namespace to default and PVC Name to cnfs-nas-pvc to view capacity in the Total Capacity area.

   

Best practices

Apply these recommendations when using NAS volume auto-scaling in production.