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This commit add some more details like helper or utility functions which will be introduced as part of the effort and also add some more details about the CSI operations a particular identified change touches. Signed-off-by: Humble Chirammal <hchiramm@redhat.com>
129 lines
6.2 KiB
Markdown
129 lines
6.2 KiB
Markdown
# 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. This will be an opt-in feature turned on at
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cluster creation time that will redirect in-tree plugin operations to a
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corresponding CSI Driver. The main mechanism we will use to migrate plugins is
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redirecting in-tree operation calls to the CSI Driver instead of the in-tree
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driver, the external components will pick up these in-tree PV's and use a
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translation library to translate to CSI Source. For more information on CSI
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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 as like any other CSI
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request, Kubernetes storage admin supposed to create a clusterID based on the
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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 like create volume. Thus, CSI operations are unchanged or untouched
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wrt to the clusterID field. In other words, for Ceph CSI this is yet another
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request coming in from a client with required parameters. This is an opaque/NOOP
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change from the Ceph CSI side for its operations, however mentioning it here as
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a reference.
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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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This volume handle is introduced as the existing in-tree volume does not have
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the volume ID format (
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ex: `0001-0020-b7f67366bb43f32e07d8a261a7840da9 -0000000000000002-c867ff35-3f04-11ec-b823-0242ac110003`)
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which Ceph CSI use by default. However, Ceph CSI need certain information like
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clusterID, pool, Image name to perform deletion and expansion of the volumes.
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The existing in-tree
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volume's `NodeStageVolume, NodePublishVolume, NodeUnstageVolume, NodeUnpublishVolume`
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operations should work without any issues as those will be tracked as static
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volumes for the CSI driver. For `DeleteVolume and ControllerExpandVolume`
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operations, from above migration specific volume ID, the CSI driver can derive
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the required details and connect to the backend cluster ( as it carry
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information like monitors, pool and image name) then perform deletion of the
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image or perform resize operation.
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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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CreateVolume, DeleteVolume, NodeStage and ExpandVolume has to validate the
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secret and use for its operations:
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## Helper functions
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Few helper/utility functions will be introduced as part of this effort to handle
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migration specific logic to it.
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internal/rbd/migration.go
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* isMigrationVolID() - Identify the volume ID is of above-mentioned form of
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migration volume ID.
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* parseMigrationVolID() - Parse the migration volume ID and populate the
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required information like `pool`, `image`, `clusterID`..etc. into
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`migrationVolID` structure.
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* deleteMigratedVolume() - Deletes the volume from the cluster by making use of
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the `migrationVolID` structure fields like `pool, image, clusterID`.
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internal/util/credentials.go
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* isMigrationSecret() - Identify the passed in secret is a migration secret
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based on the map values (ex: `key` field) of request secret.
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* NewUserCredentialsWithMigration() - This take request secret map as input and
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validate whether it is migration secret with the help of isMigrationSecret(),
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and return credentials by calling NewUserCredentials().
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* ParseAndSetSecretMapFromMigSecret() - Parse the secret map from the migration
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request and return a map with adjusted secret fields for the CSI driver to
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continue performing secret specific operations.
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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) |