Share an NFS volume across namespaces

07/18/2024 Contributors

Using Astra Trident, you can create a volume in a primary namespace and share it in one or more secondary namespaces.

Features

The Astra TridentVolumeReference CR allows you to securely share ReadWriteMany (RWX) NFS volumes across one or more Kubernetes namespaces. This Kubernetes-native solution has the following benefits:

Multiple levels of access control to ensure security
Works with all Trident NFS volume drivers
No reliance on tridentctl or any other non-native Kubernetes feature

This diagram illustrates NFS volume sharing across two Kubernetes namespaces.

A conceptual diagram of cross namespace sharing.

Quick start

You can set up NFS volume sharing in just a few steps.

Configure source PVC to share the volume

The source namespace owner grants permission to access the data in the source PVC.

Grant permission to create a CR in the destination namespace

The cluster administrator grants permission to the owner of the destination namespace to create the TridentVolumeReference CR.

Create TridentVolumeReference in the destination namespace

The owner of the destination namespace creates the TridentVolumeReference CR to refer to the source PVC.

Create the subordinate PVC in the destination namespace

The owner of the destination namespace creates the subordinate PVC to use the data source from the source PVC.

Configure the source and destination namespaces

To ensure security, cross namespace sharing requires collaboration and action by the source namespace owner, cluster administrator, and destination namespace owner. The user role is designated in each step.

Steps

Source namespace owner: Create the PVC (pvc1) in the source namespace that grants permission to share with the destination namespace (namespace2) using the shareToNamespace annotation.

kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: pvc1
  namespace: namespace1
  annotations:
    trident.netapp.io/shareToNamespace: namespace2
spec:
  accessModes:
    - ReadWriteMany
  storageClassName: trident-csi
  resources:
    requests:
      storage: 100Gi

Astra Trident creates the PV and its backend NFS storage volume.

You can share the PVC to multiple namespaces using a comma-delimited list. For example, trident.netapp.io/shareToNamespace: namespace2,namespace3,namespace4.
You can share to all namespaces using *. For example, trident.netapp.io/shareToNamespace: *
You can update the PVC to include the shareToNamespace annotation at any time.

Cluster admin: Create the custom role and kubeconfig to grant permission to the destination namespace owner to create the TridentVolumeReference CR in the destination namespace.

Destination namespace owner: Create a TridentVolumeReference CR in the destination namespace that refers to the source namespace pvc1.

apiVersion: trident.netapp.io/v1
kind: TridentVolumeReference
metadata:
  name: my-first-tvr
  namespace: namespace2
spec:
  pvcName: pvc1
  pvcNamespace: namespace1

Destination namespace owner: Create a PVC (pvc2) in destination namespace (namespace2) using the shareFromPVC annotation to designate the source PVC.

kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  annotations:
    trident.netapp.io/shareFromPVC: namespace1/pvc1
  name: pvc2
  namespace: namespace2
spec:
  accessModes:
    - ReadWriteMany
  storageClassName: trident-csi
  resources:
    requests:
      storage: 100Gi

The size of the destination PVC must be less than or equal than the source PVC.

Results

Astra Trident reads the shareFromPVC annotation on the destination PVC and creates the destination PV as a subordinate volume with no storage resource of its own that points to the source PV and shares the source PV storage resource. The destination PVC and PV appear bound as normal.

Delete a shared volume

You can delete a volume that is shared across multiple namespaces. Astra Trident will remove access to the volume on the source namespace and maintain access for other namespaces that share the volume. When all namespaces that reference the volume are removed, Astra Trident deletes the volume.

Use `tridentctl get` to query subordinate volumes

Using the tridentctl utility, you can run the get command to get subordinate volumes. For more information, refer to tridentctl commands and options.

Usage:
  tridentctl get [option]

Flags:

`-h, --help: Help for volumes.
--parentOfSubordinate string: Limit query to subordinate source volume.
--subordinateOf string: Limit query to subordinates of volume.

Limitations

Astra Trident cannot prevent destination namespaces from writing to the shared volume. You should use file locking or other processes to prevent overwriting shared volume data.
You cannot revoke access to the source PVC by removing the shareToNamespace or shareFromNamepace annotations or deleting the TridentVolumeReference CR. To revoke access, you must delete the subordinate PVC.
Snapshots, clones, and mirroring are not possible on subordinate volumes.

For more information

To learn more about cross-namespace volume access:

Visit Sharing volumes between namespaces: Say hello to cross-namespace volume access.
Watch the demo on NetAppTV.