Container Service for Kubernetes:Migrate FlexVolume to CSI for clusters that store no data

Differences between FlexVolume and CSI

The following table describes the differences between CSI and FlexVolume.

Scenarios

The CSI plug-in is more stable and efficient than the FlexVolume plug-in. In the following scenarios, we recommend that you migrate FlexVolume to CSI:

• No volume has been mounted to the cluster by using FlexVolume and no data is stored in the cluster by using FlexVolume.

• Volumes were mounted to the cluster by using FlexVolume but the relevant data in the volumes is deleted. No data is stored in the cluster by using FlexVolume.

Step 1: Uninstall FlexVolume

1. Log on to the OpenAPI Explorer console and call the UnInstallClusterAddons operation to uninstall the FlexVolume plug-in.

   • ClusterId: Set the value to the ID of your cluster. You can view the cluster ID on the Basic Information tab of the cluster details page of your cluster.

   • name: Set the value to Flexvolume.

   For more information, see Uninstall components from a cluster.

2. Run the following command to delete the alicloud-disk-controller and alicloud-nas-controller components:

   kubectl delete deploy -n kube-system alicloud-disk-controller alicloud-nas-controller

3. Run the following command to check whether the FlexVolume plug-in is uninstalled from your cluster:

   kubectl get pods -n kube-system | grep 'flexvolume\|alicloud-disk-controller\|alicloud-nas-controller'

   If no output is displayed, the FlexVolume plug-in is uninstalled from your cluster.

4. Run the following command to delete the StorageClass that uses FlexVolume from the cluster. The provisioner of the StorageClass that uses FlexVolume is alicloud/disk.

   kubectl delete storageclass alicloud-disk-available alicloud-disk-efficiency alicloud-disk-essd alicloud-disk-ssd

   Expected output:

   storageclass.storage.k8s.io "alicloud-disk-available" deleted
   storageclass.storage.k8s.io "alicloud-disk-efficiency" deleted
   storageclass.storage.k8s.io "alicloud-disk-essd" deleted
   storageclass.storage.k8s.io "alicloud-disk-ssd" deleted

   If the preceding output is displayed, the StorageClass is deleted from your cluster.

Step 2: Install the CSI plug-in

• If you use the csi-compatible-controller plug-in in a cluster, a CSI plug-in is already installed in the cluster. However, this CSI plug-in is a customized CSI plug-in instead of a standard CSI plug-in. You must run the following command to delete the customized CSI plug-in before you install the standard CSI plug-in:

  kubectl delete deploy csi-provisioner -n kube-system
  kubectl delete ds csi-plugin -n kube-system
  kubectl delete csidriver diskplugin.csi.alibabacloud.com nasplugin.csi.alibabacloud.com ossplugin.csi.alibabacloud.com

  Note

  When you delete the customized CSI plug-in from the cluster, the existing pods in the cluster are not affected. However, after you delete the customized CSI plug-in from the cluster, the pods in the cluster cannot be changed until the standard CSI plug-in is installed.

• If you do not use the csi-compatible-controller plug-in in the cluster, you can call an API operation to install the standard CSI plug-in.

1. Log on to the OpenAPI Explorer console and call the InstallClusterAddons to install the CSI plug-in.

   • ClusterId: Set the value to the ID of your cluster.

   • name: Set the value to csi-provisioner.

   • version: The latest version is automatically specified. For more information about CSI versions, see csi-provisioner.

   For more information about how to install the CSI plug-in, see Install a component in an ACK cluster.

2. Run the following command to check whether the CSI plug-in runs as expected in your cluster:

   kubectl get pods -n kube-system | grep csi

   Expected output:

   csi-plugin-577mm                              4/4     Running   0          3d20h
   csi-plugin-k9mzt                              4/4     Running   0          41d
   csi-provisioner-6b58f46989-8wwl5              9/9     Running   0          41d
   csi-provisioner-6b58f46989-qzh8l              9/9     Running   0          6d20h

   If the preceding output is displayed, the CSI plug-in runs as expected in the cluster.

Step 3: Modify the configurations of all node pools in the cluster

The configurations of a node pool change after the volume plug-in of a cluster change. After you install the new standard CSI plug-in in your cluster, the configurations of original node pools in the cluster do not automatically change. In this case, you need to manually update the configurations of these node pools. If the update is successful, the kubelet parameter --enable-controller-attach-detach is set to true on newly added nodes.

You can modify the configurations of each node pool to update the volume plug-in by adding a new instance type or changing the logon password. This way, the system automatically updates the node initialization script in the background to ensure that newly added nodes use the new configurations.

1. Log on to the ACK console. In the navigation pane on the left, click Clusters.

2. On the Clusters page, find the cluster to manage and click its name. In the left-side navigation pane, choose Nodes > Node Pools.

3. On the Node Pools page, find the target node pool and click Edit in the Actions column.

4. In the dialog box that appears, modify the node pool configurations, then click Confirm.

   Note

   This modification is intended to trigger an update of the cluster volume plug-in in the background. After the node pool configuration changes take effect, you can revert to the original settings.

Step 4: Modify the configurations of existing nodes

Use the following YAML template to modify Kubelet parameters for CSI plug-in compatibility. This DaemonSet can change the value of the kubelet parameter --enable-controller-attach-detach of existing nodes to true. After this step is complete, the DaemonSet can be deleted.

kind: DaemonSet
apiVersion: apps/v1
metadata:
  name: kubelet-set
spec:
  selector:
    matchLabels:
      app: kubelet-set
  template:
    metadata:
      labels:
        app: kubelet-set
    spec:
      tolerations:
        - operator: "Exists"
      hostNetwork: true
      hostPID: true
      containers:
        - name: kubelet-set
          securityContext:
            privileged: true
            capabilities:
              add: ["SYS_ADMIN"]
            allowPrivilegeEscalation: true
          image: registry.cn-hangzhou.aliyuncs.com/acs/csi-plugin:v1.26.5-56d1e30-aliyun
          imagePullPolicy: "Always"
          env:
          - name: enableADController
            value: "true"
          command: ["sh", "-c"]
          args:
          - echo "Starting kubelet flag set to $enableADController";
            ifFlagTrueNum=`cat /host/etc/systemd/system/kubelet.service.d/10-kubeadm.conf | grep enable-controller-attach-detach=$enableADController | grep -v grep | wc -l`;
            echo "ifFlagTrueNum is $ifFlagTrueNum";
            if [ "$ifFlagTrueNum" = "0" ]; then
                curValue="true";
                if [ "$enableADController" = "true" ]; then
                    curValue="false";
                fi;
                sed -i "s/enable-controller-attach-detach=$curValue/enable-controller-attach-detach=$enableADController/" /host/etc/systemd/system/kubelet.service.d/10-kubeadm.conf;
                restartKubelet="true";
                echo "current value is $curValue, change to expect "$enableADController;
            fi;
            if [ "$restartKubelet" = "true" ]; then
                /nsenter --mount=/proc/1/ns/mnt systemctl daemon-reload;
                /nsenter --mount=/proc/1/ns/mnt service kubelet restart;
                echo "restart kubelet";
            fi;
            while true;
            do
                sleep 5;
            done;
          volumeMounts:
          - name: etc
            mountPath: /host/etc
      volumes:
        - name: etc
          hostPath:
            path: /etc