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85 lines
3.9 KiB
Markdown
85 lines
3.9 KiB
Markdown
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# In-tree storage plugin to CSI Driver Migration
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Prior to CSI, Kubernetes provided a powerful volume plugin system. These volume
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plugins were “in-tree” meaning their code was part of the core Kubernetes code
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and shipped with the core Kubernetes binaries. The CSI migration effort enables
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the replacement of existing in-tree storage plugins such as kubernetes.io/rbd
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with a corresponding CSI driver. For more information on CSI migration effort
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refer [design doc](https://github.com/kubernetes/community/blob/master/contributors/design-proposals/storage/csi-migration.md)
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## RBD in-tree plugin to CSI migration
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This feature is tracked in Kubernetes for v1.23 as alpha under
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[RBD in-tree migration KEP](https://github.com/kubernetes/enhancements/issues/2923)
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. Below are the changes identified in the design discussions to enable CSI
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migration for RBD plugin:
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### ClusterID field in the migration request
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Considering the `clusterID` field is a required one for CSI, but in-tree
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StorageClass has `monitors` field as a required thing the clusterID will be sent
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from the migration library based on the monitors field, Kubernetes storage admin
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supposed to create a clusterID based on the monitors hash ( ex: `#md5sum <<<
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"<monaddress:port>"`) in the CSI config map and keep the monitors under this
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configuration before enabling the migration. While CSI driver receive the volume
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ID it will look at the configmap and figure out the monitors to do the
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operations. Thus, CSI operations are unchanged or untouched wrt to the clusterID
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field.
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### New Volume ID for existing volume operations
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The existing volume will have a volume ID passed in similar to the following
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format:
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```
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mig_mons-<monitors-hash>_image-<imageUUID>_<pool-hash>
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```
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Details on the hash values:
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* Monitors Hash: this carry a hash value (md5sum) which will be acted as the
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`clusterID` for the operations in this context.
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* ImageUUID: this is the unique UUID generated by Kubernetes for the created
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volume.
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* PoolHash: this is an encoded string of pool name.
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The existing in-tree volume's node operations should work without any issues as
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those will be tracked as static volumes for the CSI driver. From above volume
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ID, the CSI driver can also connect to the backend cluster and clean/delete the
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image. The migration volume ID carry the information like monitors, pool and
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image name which is good enough for the driver to identify and connect to the
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backend cluster for its operations. With above volume ID in place, we will be
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able to support mount, unmount, delete and resize operations.
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### Migration secret for CSI operations
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The in-tree secret has a data field called `key` which is the base64 admin
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secret key. The ceph CSI driver currently expect the secret to contain data
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field `UserKey` for the equivalent. The CSI driver also expect the `UserID`
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field which is not available in the in-tree secret by default. This
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missing `userID` will be filled (if the username differ than `admin`) in the
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migration secret as `adminId` field in the migration request, ie:
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`key` field value will be picked up from the migration secret to `UserKey`
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field.
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`adminId` field value will be picked up from the migration secret to `UserID`
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field
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if `adminId` field is nil or not set, `UserID` field will be filled with default
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value ie `admin`.The above logic get activated only when the secret is a
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migration secret, otherwise skipped to the normal workflow as we have today.
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## CephFS in-tree plugin to CSI migration
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This is yet to be done and tracked
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at [CephFS in-tree migration KEP](https://github.com/kubernetes/enhancements/issues/2924)
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### Additional Reference
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[Kubernetes 1.17 Feature: Kubernetes In-Tree to CSI Volume Migration Moves to Beta](https://kubernetes.io/blog/2019/12/09/kubernetes-1-17-feature-csi-migration-beta/)
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[Tracker Issue in Ceph CSI](https://github.com/ceph/ceph-csi/issues/2509)
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[In-tree storage plugin to CSI Driver Migration KEP](https://github.com/kubernetes/enhancements/issues/625)
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