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Merge pull request kubernetes#321 from gnufied/mount-option-design-prop
Add proposal for mount options
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# Mount options for mountable volume types | ||
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## Goal | ||
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Enable Kubernetes admins to specify mount options with mountable volumes | ||
such as - `nfs`, `glusterfs` or `aws-ebs` etc. | ||
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## Motivation | ||
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We currently support network filesystems: NFS, Glusterfs, Ceph FS, SMB (Azure file), Quobytes, and local filesystems such as ext[3|4] and XFS. | ||
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Mount time options that are operationally important and have no security implications should be suppported. Examples are NFS's TCP mode, versions, lock mode, caching mode; Glusterfs's caching mode; SMB's version, locking, id mapping; and more. | ||
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## Design | ||
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We are going to add support for mount options in PVs as a beta feature to begin with. | ||
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Mount options can be specified as `mountOptions` annotations in PV. For example: | ||
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``` yaml | ||
apiVersion: v1 | ||
kind: PersistentVolume | ||
metadata: | ||
name: pv0003 | ||
annotations: | ||
volume.beta.kubernetes.io/mountOptions: "hard,nolock,nfsvers=3" | ||
spec: | ||
capacity: | ||
storage: 5Gi | ||
accessModes: | ||
- ReadWriteOnce | ||
persistentVolumeReclaimPolicy: Recycle | ||
nfs: | ||
path: /tmp | ||
server: 172.17.0.2 | ||
``` | ||
## Preventing users from specifying mount options in inline volume specs of Pod | ||
While mount options enable more flexibility in how volumes are mounted, it can result | ||
in user specifying options that are not supported or are known to be problematic when | ||
using inline volume specs. | ||
After much deliberation it was decided that - `mountOptions` as an API parameter will not be supported | ||
for inline volume specs. | ||
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### Error handling and plugins that don't support mount option | ||
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Kubernetes ships with volume plugins that don't support any kind of mount options. Such as `configmaps` or `secrets`, | ||
in those cases to prevent user from submitting volume definitions with bogus mount options - plugins can define a interface function | ||
such as: | ||
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```go | ||
func SupportsMountOption() { | ||
return false | ||
} | ||
``` | ||
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which will be used to validate the PV definition and API object will be *only* created if it passes the validation. Additionally | ||
support for user specified mount options will be also checked when volumes are being mounted. | ||
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In other cases where plugin supports mount options (such as - `NFS` or `GlusterFS`) but mounting fails because of invalid mount | ||
option or otherwise - an Event API object will be created and attached to the appropriate object. |