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| -rw-r--r-- | contributors/design-proposals/storage/csi-migration.md | 65 |
1 files changed, 47 insertions, 18 deletions
diff --git a/contributors/design-proposals/storage/csi-migration.md b/contributors/design-proposals/storage/csi-migration.md index 5aa7411c..ee6dc464 100644 --- a/contributors/design-proposals/storage/csi-migration.md +++ b/contributors/design-proposals/storage/csi-migration.md @@ -237,26 +237,55 @@ with the in-tree plugin, the VolumeAttachment object becomes orphaned. ### In-line Volumes In-line controller calls are a special case because there is no PV. In this case -we will add the CSI Source JSON to the VolumeToAttach object and in Attach we -will put the Source in a new field in the VolumeAttachment object -VolumeAttachment.Spec.Source.VolumeAttachmentSource.InlineVolumeSource. The CSI Attacher will have to -be modified to also check this location for a source before checking the PV -itself. +we will forward the in-tree volume source to CSI attach as-is and it will be +copied to a new field in the VolumeAttachment object +VolumeAttachment.Spec.Source.VolumeAttachmentSource.InlineVolumeSource. The +VolumeAttachment name must be made with the CSI Translated version of the +VolumeSource in order for it to be discoverable by Detach and WaitForAttach +(described in more detail below). + +The CSI Attacher will have to be modified to also check this location for a +source as well as checking for the `pvName`. Only one of the two may be +specified. + +The new VolumeAttachmentSource API will look as such: +``` +// VolumeAttachmentSource represents a volume that should be attached. +// Right now only PersistenVolumes can be attached via external attacher, +// in future we may allow also inline volumes in pods. +// Exactly one member can be set. +type VolumeAttachmentSource struct { + // Name of the persistent volume to attach. + // +optional + PersistentVolumeName *string `json:"persistentVolumeName,omitempty" protobuf:"bytes,1,opt,name=persistentVolumeName"` + + // Allows CSI migration code to copy an inline volume + // source from a pod to the VolumeAttachment to support shimming of + // in-tree inline volumes to a CSI backend. + // This field is alpha-level and is only honored by servers that enable the CSIMigration feature. + // +optional + InlineVolumeSource *v1.VolumeSource `json:"inlineVolumeSource,omitempty protobuf:"bytes,2,opt,name=inlineVolumeSource"` +} +``` We need to be careful with naming VolumeAttachments for in-line volumes. The -name needs to be unique and ADC must be able to find the right -VolumeAttachment when a pod is deleted (i.e. using only info in Node.Status). -CSI driver in kubelet must be able to find the VolumeAttachment too to get -AttachmentMetadata for NodeStage/NodePublish. - -In downgrade scenario where the migration is then turned off we will have to -remove these floating VolumeAttachment objects, the same issue is outlined above -in the Non-Dynamic Provisioned Volumes section. - -For more details on this see the PR that specs out CSI Inline Volumes in more detail: -https://github.com/kubernetes/community/pull/2273. Basically we will just translate -the in-tree inline volumes into the format specified/implemented in the -container-storage-interface-inline-volumes proposal. +name needs to be unique and ADC must be able to find the right VolumeAttachment +when a pod is deleted (i.e. using only info in Node.Status). CSI driver in +kubelet must be able to find the VolumeAttachment too to call WaitForAttach and +VolumesAreAttached. + +The attachment name is usually a hash of the volume name, CSI Driver name, and +Node name. We are able to get all this information for Detach and WaitForAttach +by translating the in-tree inline volume source to a CSI volume source before +passing it to to the volume operations. + +There is currently a race condition in in-tree inline volumes where if a pod +object is deleted and the ADC restarts we lose the information for the inline +volume and will not be able to detach the volume. This is a known issue and we +will retain the same behavior with migrated inline volumes. However, we may be +able to solve this in the future by reconciling the VolumeAttachment object with +existing Pods in the ADC. + ### Volume Resize |