Node Driver Registrar

The node-driver-registrar is a sidecar container that registers the CSI driver with Kubelet using the kubelet plugin registration mechanism.

This is necessary because Kubelet is responsible for issuing CSI NodeGetInfo, NodeStageVolume, NodePublishVolume calls. The node-driver-registrar registers your CSI driver with Kubelet so that it knows which Unix domain socket to issue the CSI calls on.

Compatibility

This information reflects the head of this branch.

Compatible with CSI Version	Container Image	Min K8s Version	Recommended K8s Version
CSI Spec v1.5.0	registry.k8s.io/sig-storage/csi-node-driver-registrar	1.13	1.23.10*

For release-0.4 and below, please refer to the driver-registrar repository.

*) On Windows, Kubernetes v1.23.10, v1.24.4, v1.25.0 or newer is required to fix handling of registration sockets. On Linux, v1.13 is the recommended version.

Usage

There are two UNIX domain sockets used by the node-driver-registrar:

Registration socket:
- Registers the driver with kubelet.
- Created by the node-driver-registrar.
- Exposed on a Kubernetes node via hostpath in the Kubelet plugin registry. (typically /var/lib/kubelet/plugins_registry/<drivername.example.com>-reg.sock). The hostpath volume must be mounted at /registration.
CSI driver socket:
- Used by kubelet to interact with the CSI driver.
- Created by the CSI driver.
- Exposed on a Kubernetes node via hostpath somewhere other than the Kubelet plugin registry. (typically /var/lib/kubelet/plugins/<drivername.example.com>/csi.sock).
- This is the socket referenced by the --csi-address and --kubelet-registration-path arguments.
- Note that before Kubernetes v1.17, if the csi socket is in the /var/lib/kubelet/plugins/ path, kubelet may log a lot of harmless errors regarding grpc GetInfo call not implemented (fix in kubernetes/kubernetes#84533). The /var/lib/kubelet/csi-plugins/ path is preferred in Kubernetes versions prior to v1.17.

Required arguments

--csi-address: This is the path to the CSI driver socket (defined above) inside the pod that the node-driver-registrar container will use to issue CSI operations (e.g. /csi/csi.sock).
--kubelet-registration-path: This is the path to the CSI driver socket on the host node that kubelet will use to issue CSI operations (e.g. /var/lib/kubelet/plugins/<drivername.example.com>/csi.sock). Note this is NOT the path to the registration socket.

Optional arguments

--http-endpoint: The TCP network address where the HTTP server for diagnostics, including the health check indicating whether the registration socket exists, will listen (example: :8080). The default is empty string, which means the server is disabled.
--health-port: (deprecated) This is the port of the health check server for the node-driver-registrar, which checks if the registration socket exists. A value <= 0 disables the server. Server is disabled by default.
--timeout <duration>: Timeout of all calls to CSI driver. It should be set to a value that accommodates the GetDriverName calls. 1 second is used by default.
--mode <mode> (default: --mode=registration): DEPRECATED. If this is set to kubelet-registration-probe, the driver will exit successfully without registering with CSI. If set to any other value node-driver-registrar will do the kubelet plugin registration. This flag will be removed in a future major release because the mode kubelet-registration-probe is no longer needed.
--enable-pprof: Enable pprof profiling on the TCP network address specified by --http-endpoint.

Required permissions

The node-driver-registrar does not interact with the Kubernetes API, so no RBAC rules are needed.

It does, however, need to be able to mount hostPath volumes and have the file permissions to:

Access the CSI driver socket (typically in /var/lib/kubelet/plugins/<drivername.example.com>/).
- Used by the node-driver-registrar to fetch the driver name from the driver contain (via the CSI GetPluginInfo() call).
Access the registration socket (typically in /var/lib/kubelet/plugins_registry/).
- Used by the node-driver-registrar to register the driver with kubelet.

Health Check with the http server

If --http-endpoint is set, the node-driver-registrar exposes a health check endpoint at the specified address and the path /healthz, indicating whether the registration socket exists.

Health Check with an exec probe

If --mode=kubelet-registration-probe is set, node-driver-registrar can act as a probe checking if kubelet plugin registration succeeded. This is useful to detect if the registration got stuck as seen in issue #143

The value of --kubelet-registration-path must be the same as the one set in the container args, --csi-address is not required in this mode, for example:

Linux

  containers:
    - name: csi-driver-registrar
      image: k8s.gcr.io/sig-storage/csi-node-driver-registrar:v2.5.0
      args:
        - "--v=5"
        - "--csi-address=/csi/csi.sock"
        - "--kubelet-registration-path=/var/lib/kubelet/plugins/<drivername.example.com>/csi.sock"
      livenessProbe:
        exec:
          command:
          - /csi-node-driver-registrar
          - --kubelet-registration-path=/var/lib/kubelet/plugins/<drivername.example.com>/csi.sock
          - --mode=kubelet-registration-probe
        initialDelaySeconds: 30
        timeoutSeconds: 15

Windows

  containers:
    - name: csi-driver-registrar
      image: k8s.gcr.io/sig-storage/csi-node-driver-registrar:v2.5.0
      args:
        - --v=5
        - --csi-address=unix://C:\\csi\\csi.sock
        - --kubelet-registration-path=C:\\var\\lib\\kubelet\\plugins\\<drivername.example.com>\\csi.sock
      livenessProbe:
        exec:
          command:
          - /csi-node-driver-registrar.exe
          - --kubelet-registration-path=C:\\var\\lib\\kubelet\\plugins\\<drivername.example.com>\\csi.sock
          - --mode=kubelet-registration-probe
        initialDelaySeconds: 30
        timeoutSeconds: 15

Related issue #143

Example

Here is an example sidecar spec in the driver DaemonSet. <drivername.example.com> should be replaced by the actual driver's name.

      containers:
        - name: csi-driver-registrar
          image: k8s.gcr.io/sig-storage/csi-node-driver-registrar:v2.5.0
          args:
            - "--csi-address=/csi/csi.sock"
            - "--kubelet-registration-path=/var/lib/kubelet/plugins/<drivername.example.com>/csi.sock"
            - "--health-port=9809"
          volumeMounts:
            - name: plugin-dir
              mountPath: /csi
            - name: registration-dir
              mountPath: /registration
          ports:
            - containerPort: 9809
              name: healthz
          livenessProbe:
            httpGet:
              path: /healthz
              port: healthz
            initialDelaySeconds: 5
            timeoutSeconds: 5
      volumes:
        - name: registration-dir
          hostPath:
            path: /var/lib/kubelet/plugins_registry/
            type: Directory
        - name: plugin-dir
          hostPath:
            path: /var/lib/kubelet/plugins/<drivername.example.com>/
            type: DirectoryOrCreate

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