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71 lines
3.2 KiB
Markdown
71 lines
3.2 KiB
Markdown
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# Dynamic provisioning of NFS volumes
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Ceph has [support for NFS-Ganesha to export directories][ceph_mgr_nfs] on
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CephFS. This can be used to export CephFS based volumes over NFS.
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## Node-Plugin for mounting NFS-exports
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The Kubernetes CSI community provides and maintains a [NFS CSI][nfs_csi]
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driver. This driver can be used as a Node-Plugin so that NFS CSI volumes can be
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mounted. When a CSI volume has the `server` and `share`
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[parameters][nfs_csi_params], the Node-Plugin will be able to mount the
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NFS-export.
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## Exporting CephFS based volumes over NFS
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Ceph-CSI already creates CephFS volumes, that can be mounted over the native
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CephFS protocol. A new provisioner in Ceph-CSI can create CephFS volumes, and
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include the required [NFS CSI parameters][nfs_csi_params] so that the [NFS CSI
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driver][nfs_csi] can mount the CephFS volume over NFS.
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The provisioner that handles the CSI requests for NFS volume can call the [Ceph
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Mgr commands to export/unexport][ceph_mgr_nfs] the CephFS volumes. The CephFS
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volumes would be internally managed by the NFS provisioner, and only be exposed
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as NFS CSI volumes towards the consumers.
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### `CreateVolume` CSI operation
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When the Ceph-CSI NFS provisioner is requested to create a NFS CSI volume, the
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following steps need to be taken:
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1. create a CephFS volume, use the CephFS `CreateVolume` call or other internal
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API
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1. call the Ceph Mgr API to export the CephFS volume with NFS-Ganesha
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1. return the NFS CSI volume, with `server` and `share` parameters (other
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parameters that are useful for CephFS volume management may be kept)
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The 2nd step requires a NFS-cluster name for the Ceph Mgr call(s). The name of
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the NFS-cluster as managed by Ceph should be provided in the parameters of the
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`CreateVolume` operation. For Kubernetes that means the parameters is set as an
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option in the `StorageClass`.
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The `server` parameter of the volume is an other option that is managed by the
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Ceph (or Rook) infrastructure. This parameter is also required to be provided
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in the `CreateVolume` parameters.
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Removing the NFS-export for the volume (or other operations) requires the name
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of the NFS-cluster, as it is needed for the Ceph Mgr API. Like other parameters
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of the CephFS volume, it will be needed to store the NFS-cluster name in the
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OMAP journalling.
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### `DeleteVolume` CSI operation
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The `DeleteVolume` operation only receives the `volume_id` parameter, which
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is to be used by the CSI Controller (provisioner) to locate the backing volume.
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The `DeleteVolume` operation for the CephFS provisioner already knows how to
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delete volumes by ID.
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In order to remove the exported volume from the NFS-cluster, the operation
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needs to fetch the name of the NFS-cluster from the journal where it was stored
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during `CreateVolume`.
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### Additional CSI operations
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`CreateVolume` and `DeleteVolume` are the only required operations for the CSI
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Controller (provisioner). Additional features as they are supported by CephFS
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can forward the operations to the CephFS provisioner at a later time.
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[ceph_mgr_nfs]: https://docs.ceph.com/en/latest/mgr/nfs/
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[nfs_csi]: https://github.com/kubernetes-csi/csi-driver-nfs
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[nfs_csi_params]: https://github.com/kubernetes-csi/csi-driver-nfs/blob/master/docs/driver-parameters.md
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