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Release 1.8 (#5659)

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* GC now supports non-core resources

* Add two examples about how to analysis audits of kube-apiserver (#4264)

* Deprecate system:nodes binding

* [1.8] StatefulSet `initialized` annotation is now ignored.

* inits the kubeadm upgrade docs

addresses kubernetes/kubernetes.github.io/issues/4689

* adds kubeadm upgrade cmd to ToC

addresses kubernetes/kubernetes.github.io/issues/4689

* add workload placement docs

* ScaleIO - document udpate for 1.8

* Add documentation on storageClass.mountOptions and PV.mountOptions (#5254)

* Add documentation on storageClass.mountOptions and PV.mountOptions

* convert notes into callouts

* Add docs for CustomResource validation

add info about supported fields

* advanced audit beta features (#5300)

* Update job workload doc with backoff failure policy (#5319)

Add to the Jobs documentation how to use the new backoffLimit field that
limit the number of Pod failure before considering the Job as failed.

* Documented additional AWS Service annotations (#4864)

* Add device plugin doc under concepts/cluster-administration. (#5261)

* Add device plugin doc under concepts/cluster-administration.

* Update device-plugins.md

* Update device-plugins.md

Add meta description. Fix typo. Change bare metal deployment to manual deployment.

* Update device-plugins.md

Fix typo again.

* Update page.version. (#5341)

* Add documentation on storageClass.reclaimPolicy (#5171)

* [Advanced audit] use new herf for audit-api (#5349)

This tag contains all the changes in v1beta1 version. Update it now.

* Added documentation around creating the InitializerConfiguration for the persistent volume label controller in the cloud-controller-manager (#5255)

* Documentation for kubectl plugins (#5294)

* Documentation for kubectl plugins

* Update kubectl-plugins.md

* Update kubectl-plugins.md

* Updated CPU manager docs to match implementation. (#5332)

* Noted limitation of alpha static cpumanager.

* Updated CPU manager docs to match implementation.

- Removed references to CPU pressure node condition and evictions.
- Added note about new --cpu-manager-reconcile-period flag.
- Added note about node allocatable requirements for static policy.
- Noted limitation of alpha static cpumanager.

* Move cpu-manager task link to rsc mgmt section.

* init containers annotation removed in  1.8 (#5390)

* Add documentation for TaintNodesByCondition (#5352)

* Add documentation for TaintNodesByCondition

* Update nodes.md

* Update taint-and-toleration.md

* Update daemonset.md

* Update nodes.md

* Update taint-and-toleration.md

* Update daemonset.md

* Fix deployments (#5421)

* Document extended resources and OIR deprecation. (#5399)

* Document extended resources and OIR deprecation.

* Updated extended resources doc per reviews.

* reverts extra spacing in _data/tasks.yml

* addresses `kubeadm upgrade` review comments

Feedback from @chenopis, @luxas, and @steveperry-53 addressed with this commit

* HugePages documentation (#5419)

* Update cpu-management-policies.md (#5407)

Fixed the bad link.
Modified "cpu" to "CPU".
Added more 'yaml' as supplement.

* Update RBAC docs for v1 (#5445)

* Add user docs for pod priority and preemption (#5328)

* Add user docs for pod priority and preemption

* Update pod-priority-preemption.md

* More updates

* Update docs/admin/kubeadm.md for 1.8 (#5440)

- Made a couple of minor wording changes (not strictly 1.8 related).
 - Did some reformatting (not strictly 1.8 related).
 - Updated references to the default token TTL (was infinite, now 24 hours).
 - Documented the new `--discovery-token-ca-cert-hash` and `--discovery-token-unsafe-skip-ca-verification` flags for `kubeadm join`.
 - Added references to the new `--discovery-token-ca-cert-hash` flag in all the default examples.
 - Added a new _Security model_ section that describes the security tradeoffs of the various discovery modes.
 - Documented the new `--groups` flag for `kubeadm token create`.
 - Added a note of caution under _Automating kubeadm_ that references the _Security model_ section.
 - Updated the component version table to drop 1.6 and add 1.8.
 - Update `_data/reference.yml` to try to get the sidebar fixed up and more consistent with `kubefed`.

* Update StatefulSet Basics for 1.8 release (#5398)

* addresses `kubeadm upgrade` review comments

2nd iteration review comments by @luxas

* adds kubelet upgrade section to kubeadm upgrade

* Fix a bulleted list on docs/admin/kubeadm.md. (#5458)

I updated this doc yesterday and I was absolutely sure I fixed this, but I just saw that this commit got lost somehow.

This was introduced recently in https://github.com/kubernetes/kubernetes.github.io/pull/5440.

* Clarify the API to check for device plugins

* Moving Flexvolume to separate out-of-tree section

* addresses `kubeadm upgrade` review comments

CC: @luxas

* fixes kubeadm upgrade index

* Update Stackdriver Logging documentation (#5495)

* Re-update WordPress and MySQL PV doc to use apps/v1beta2 APIs (#5526)

* Update statefulset concepts doc to use apps/v1beta2 APIs (#5420)

* add document on kubectl's behavior regarding initializers (#5505)

* Update docs/admin/kubeadm.md to cover self-hosting in 1.8. (#5497)

This is a new beta feature in 1.8.

* Update kubectl patch doc to use apps/v1beta2 APIs (#5422)

* [1.8] Update "Run Applications" tasks to apps/v1beta2. (#5525)

* Update replicated stateful application task for 1.8.

* Update single instance stateful app task for 1.8.

* Update stateless app task for 1.8.

* Update kubectl patch task for 1.8.

* fix the link of persistent storage (#5515)

* update the admission-controllers.md index.md what-is-kubernetes.md link

* fix the link of persistent storage

* Add quota support for local ephemeral storage (#5493)

* Add quota support for local ephemeral storage

update the doc to this alpha feature

* Update resource-quotas.md

* Updated Deployments concepts doc (#5491)

* Updated Deployments concepts doc

* Addressed comments

* Addressed more comments

* Modify allocatable storage to ephemeral-storage (#5490)

Update the doc to use ephemeral-storage instead of storage

* Revamped concepts doc for ReplicaSet (#5463)

* Revamped concepts doc for ReplicaSet

* Minor changes to call out specific versions for selector defaulting and
immutability

* Addressed doc review comments

* Remove petset documentations (#5395)

* Update docs to use batch/v1beta1 cronjobs (#5475)

* add federation job doc (#5485)

* add federation job doc

* Update job.md

Edits for clarity and consistency

* Update job.md

Fixed a typo

* update DaemonSet concept for 1.8 release (#5397)

* update DaemonSet concept for 1.8 release

* Update daemonset.md

Fix typo. than -> then

* Update bootstrap tokens doc for 1.8. (#5479)

* Update bootstrap tokens doc for 1.8.

This has some changes I missed when I was updating the main kubeadm documention:
 - Bootstrap tokens are now beta, not alpha (https://github.com/kubernetes/features/issues/130)
 - The apiserver flag to enable the authenticator changedin 1.8 (https://github.com/kubernetes/kubernetes/pull/51198)
 - Added `auth-extra-groups` documentaion (https://github.com/kubernetes/kubernetes/pull/50933)
 - Updated the _Token Management with `kubeadm`_ section to link to the main kubeadm docs, since it was just duplicated information.

* Update bootstrap-tokens.md

* Updated the Cassandra tutorial to use apps/v1beta2 (#5548)

* add docs for AllowPrivilegeEscalation (#5448)

Signed-off-by: Jess Frazelle <acidburn@microsoft.com>

* Add local ephemeral storage alpha feature in managing compute resource (#5522)

* Add local ephemeral storage alpha feature in managing compute resource

Since 1.8, we add the local ephemeral storage alpha feature as one
resource type to manage. Add this feature into the doc.

* Update manage-compute-resources-container.md

* Update manage-compute-resources-container.md

* Update manage-compute-resources-container.md

* Update manage-compute-resources-container.md

* Update manage-compute-resources-container.md

* Update manage-compute-resources-container.md

* Added documentation for Metrics Server (#5560)

* authorization: improve authorization debugging docs (#5549)

* Document mount propagation (#5544)

* Update /docs/setup/independent/create-cluster-kubeadm.md for 1.8. (#5524)

This introduction needed a couple of small tweaks to cover the `--discovery-token-ca-cert-hash` flag added in https://github.com/kubernetes/kubernetes/pull/49520 and some version bumps.

* Add task doc for alpha dynamic kubelet configuration (#5523)

* Fix input/output of selfsubjectaccess review (#5593)

* Add docs for implementing resize (#5528)

* Add docs for implementing resize

* Update admission-controllers.md

* Added link to PVC section

* minor typo fixes

* Update NetworkPolicy concept guide with egress and CIDR changes (#5529)

* update zookeeper tutorial for 1.8 release

* add doc for hostpath type (#5503)

* Federated Hpa feature doc (#5487)

* Federated Hpa feature doc

* Federated Hpa feature doc review fixes

* Update hpa.md

* Update hpa.md

* update cloud controller manager docs for v1.8

* Update cronjob with defaults information (#5556)

* Kubernetes 1.8 reference docs (#5632)

* Kubernetes 1.8 reference docs

* Kubectl reference docs for 1.8

* Update side bar with 1.8 kubectl and api ref docs links

* remove petset.md

* update on state of HostAlias in 1.8 with hostNetwork Pod support (#5644)

* Fix cron job deletion section (#5655)

* update imported docs (#5656)

* Add documentation for certificate rotation. (#5639)

* Link to using kubeadm page

* fix the command output

fix the command output

* fix typo in api/resources reference: "Worloads"

* Add documentation for certificate rotation.

* Create TOC entry for cloud controller manager. (#5662)

* Updates for new versions of API types

* Followup 5655: fix link to garbage collection (#5666)

* Temporarily redirect resources-reference to api-reference. (#5668)

* Update config for 1.8 release. (#5661)

* Update config for 1.8 release.

* Address reviewer comments.

* Switch references in HPA docs from alpha to beta (#5671)

The HPA docs still referenced the alpha version.  This switches them to
talk about v2beta1, which is the appropriate version for Kubernetes 1.8

* Deprecate openstack heat (#5670)

* Fix typo in pod preset conflict example

Move container port definition to the correct line.

* Highlight openstack-heat provider deprecation

The openstack-heat provider for kube-up is being deprecated and will be
removed in a future release.

* Temporarily fix broken links by redirecting. (#5672)

* Fix broken links. (#5675)

* Fix render of code block (#5674)

* Fix broken links. (#5677)

* Add a small note about auto-bootstrapped CSR ClusterRoles (#5660)

* Update kubeadm install doc for v1.8 (#5676)

* add draft workloads api content for 1.8 (#5650)

* add draft workloads api content for 1.8

* edits per review, add tables, for 1.8 workloads api doc

* fix typo

* Minor fixes to kubeadm 1.8 upgrade guide. (#5678)

- The kubelet upgrade instructions should be done on every host, not
  just worker nodes.
- We should just upgrade all packages, instead of calling out kubelet
  specifically. This will also upgrade kubectl, kubeadm, and
  kubernetes-cni, if installed.
- Draining nodes should also ignore daemonsets, and master errors can be
  ignored.
- Make sure that the new kubeadm download is chmoded correctly.
- Add a step to run `kubeadm version` to verify after downloading.
- Manually approve new kubelet CSRs if rotation is enabled (known issue).

* Release 1.8 (#5680)

* Fix versions for 1.8 API ref docs

* Updates for 1.8 kubectl reference docs

* Kubeadm /docs/admin/kubeadm.md cleanup, editing. (#5681)

* Update docs/admin/kubeadm.md (mostly 1.8 related).

This is Fabrizio's work, which I'm committing along with my edits (in a commit on top of this).

* A few of my own edits to clarify and clean up some Markdown.
This commit is contained in:
Steve Perry
2017-09-28 21:46:51 -07:00
committed by GitHub
parent 88d3ed821d
commit 799eaf4229
1553 changed files with 318572 additions and 3286 deletions
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docs/concepts/storage/persistent-volumes.md
+100 -67
View File
@@ -107,7 +107,40 @@ However, the particular path specified in the custom recycler pod template in th
#### Deleting
For volume plugins that support the Delete reclaim policy, deletion removes both the `PersistentVolume` object from Kubernetes, as well as deleting the associated storage asset in the external infrastructure, such as an AWS EBS, GCE PD, Azure Disk, or Cinder volume. Volumes that were dynamically provisioned are always deleted. If that is not desired, currently, the only option is to edit or patch the PV after it is created. See [Change the Reclaim Policy of a PersistentVolume](https://kubernetes.io/docs/tasks/administer-cluster/change-pv-reclaim-policy/).
For volume plugins that support the Delete reclaim policy, deletion removes both the `PersistentVolume` object from Kubernetes, as well as deleting the associated storage asset in the external infrastructure, such as an AWS EBS, GCE PD, Azure Disk, or Cinder volume. Volumes that were dynamically provisioned inherit the [reclaim policy of their `StorageClass`](#reclaim-policy-1), which defaults to Delete. The administrator should configure the `StorageClass` according to users' expectations, otherwise the PV must be edited or patched after it is created. See [Change the Reclaim Policy of a PersistentVolume](https://kubernetes.io/docs/tasks/administer-cluster/change-pv-reclaim-policy/).
### Expanding Persistent Volumes Claims
With Kubernetes 1.8, we have added Alpha support for expanding persistent volumes. The current Alpha support was designed to only support volume types
that don't need file system resizing (Currently only glusterfs).
Administrator can allow expanding persistent volume claims by setting `ExpandPersistentVolumes` feature gate to true. Administrator
should also enable [`PersistentVolumeClaimResize` admission plugin](/docs/admin/admission-controllers/#persistentvolumeclaimresize)
to perform additional validations of volumes that can be resized.
Once `PersistentVolumeClaimResize` admission plug-in has been turned on, resizing will only be allowed for storage classes
whose `allowVolumeExpansion` field is set to true.
``` yaml
kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
name: gluster-vol-default
provisioner: kubernetes.io/glusterfs
parameters:
resturl: "http://192.168.10.100:8080"
restuser: ""
secretNamespace: ""
secretName: ""
allowVolumeExpansion: true
```
Once both feature gate and aforementioned admission plug-in are turned on, an user can request larger volume for their `PersistentVolumeClaim`
by simply editing the claim and requesting bigger size. This in turn will trigger expansion of volume that is backing underlying `PersistentVolume`.
Under no circustances a new `PersistentVolume` gets created to satisfy the claim. Kubernetes will attempt to resize existing volume to satisfy the claim.
## Types of Persistent Volumes
@@ -139,20 +172,23 @@ For volume plugins that support the Delete reclaim policy, deletion removes both
Each PV contains a spec and status, which is the specification and status of the volume.
```yaml
apiVersion: v1
kind: PersistentVolume
metadata:
name: pv0003
spec:
capacity:
storage: 5Gi
accessModes:
- ReadWriteOnce
persistentVolumeReclaimPolicy: Recycle
storageClassName: slow
nfs:
path: /tmp
server: 172.17.0.2
apiVersion: v1
kind: PersistentVolume
metadata:
name: pv0003
spec:
capacity:
storage: 5Gi
accessModes:
- ReadWriteOnce
persistentVolumeReclaimPolicy: Recycle
storageClassName: slow
mountOptions:
- hard
- nfsvers=4.1
nfs:
path: /tmp
server: 172.17.0.2
```
### Capacity
@@ -225,47 +261,14 @@ Current reclaim policies are:
Currently, only NFS and HostPath support recycling. AWS EBS, GCE PD, Azure Disk, and Cinder volumes support deletion.
### Phase
A volume will be in one of the following phases:
* Available -- a free resource that is not yet bound to a claim
* Bound -- the volume is bound to a claim
* Released -- the claim has been deleted, but the resource is not yet reclaimed by the cluster
* Failed -- the volume has failed its automatic reclamation
The CLI will show the name of the PVC bound to the PV.
### Mount Options
A Kubernetes administrator can specify additional mount options for when a Persistent Volume is being mounted on a node.
A Kubernetes administrator can specify additional mount options for when a Persistent Volume is mounted on a node.
You can specify a mount option by using the annotation `volume.beta.kubernetes.io/mount-options` on
your Persistent Volume.
**Note:** Not all Persistent volume types support mount options.
{: .note}
For example:
```yaml
apiVersion: "v1"
kind: "PersistentVolume"
metadata:
name: gce-disk-1
annotations:
volume.beta.kubernetes.io/mount-options: "discard"
spec:
capacity:
storage: "10Gi"
accessModes:
- "ReadWriteOnce"
gcePersistentDisk:
fsType: "ext4"
pdName: "gce-disk-1"
```
A mount option is a string which will be cumulatively joined and used while mounting volume to the disk.
Note that not all Persistent volume types support mount options. In Kubernetes version 1.6, the following
volume types support mount options.
The following volume types support mount options:
* GCEPersistentDisk
* AWSElasticBlockStore
@@ -281,6 +284,22 @@ volume types support mount options.
* Quobyte Volumes
* VMware Photon
Mount options are not validated, so mount will simply fail if one is invalid.
In the past, the annotation `volume.beta.kubernetes.io/mount-options` was used instead
of the `mountOptions` attribute. This annotation is still working, however
it will become fully deprecated in a future Kubernetes release.
### Phase
A volume will be in one of the following phases:
* Available -- a free resource that is not yet bound to a claim
* Bound -- the volume is bound to a claim
* Released -- the claim has been deleted, but the resource is not yet reclaimed by the cluster
* Failed -- the volume has failed its automatic reclamation
The CLI will show the name of the PVC bound to the PV.
## PersistentVolumeClaims
@@ -355,8 +374,10 @@ to Kubernetes cluster by addon manager during installation.
When a PVC specifies a `selector` in addition to requesting a `StorageClass`,
the requirements are ANDed together: only a PV of the requested class and with
the requested labels may be bound to the PVC. Note that currently, a PVC with a
non-empty `selector` can't have a PV dynamically provisioned for it.
the requested labels may be bound to the PVC.
**Note:** Currently, a PVC with a non-empty `selector` can't have a PV dynamically provisioned for it.
{: .note}
In the past, the annotation `volume.beta.kubernetes.io/storage-class` was used instead
of `storageClassName` attribute. This annotation is still working, however
@@ -390,9 +411,9 @@ spec:
## StorageClasses
Each `StorageClass` contains the fields `provisioner` and `parameters`, which
are used when a `PersistentVolume` belonging to the class needs to be
dynamically provisioned.
Each `StorageClass` contains the fields `provisioner`, `parameters`, and
`reclaimPolicy`, which are used when a `PersistentVolume` belonging to the
class needs to be dynamically provisioned.
The name of a `StorageClass` object is significant, and is how users can
request a particular class. Administrators set the name and other parameters
@@ -412,6 +433,9 @@ metadata:
provisioner: kubernetes.io/aws-ebs
parameters:
type: gp2
reclaimPolicy: Retain
mountOptions:
- debug
```
### Provisioner
@@ -455,13 +479,22 @@ There are also cases when 3rd party storage vendors provide their own external
provisioner.
### Reclaim Policy
Persistent Volumes that are dynamically created by a storage class will have a reclaim
policy of `delete`. If that is not desired, the only current option is to edit the
PV after it is created.
Persistent Volumes that are dynamically created by a storage class will have the
reclaim policy specified in the `reclaimPolicy` field of the class, which can be
either `Delete` or `Retain`. If no `reclaimPolicy` is specified when a
`StorageClass` object is created, it will default to `Delete`.
Persistent Volumes that are created manually and managed via a storage class will have
whatever reclaim policy they were assigned at creation.
### Mount Options
Persistent Volumes that are dynamically created by a storage class will have the
mount options specified in the `mountOptions` field of the class.
If the volume plugin does not support mount options but mount options are
specified, provisioning will fail. Mount options are not validated on neither
the class nor PV, so mount of the PV will simply fail if one is invalid.
### Parameters
Storage classes have parameters that describe volumes belonging to the storage
class. Different parameters may be accepted depending on the `provisioner`. For
@@ -795,8 +828,8 @@ provisioner: kubernetes.io/scaleio
parameters:
gateway: https://192.168.99.200:443/api
system: scaleio
protectionDomain: default
storagePool: default
protectionDomain: pd0
storagePool: sp1
storageMode: ThinProvisionned
secretRef: sio-secret
readOnly: false
@@ -806,12 +839,12 @@ parameters:
* `provisioner`: attribute is set to `kubernetes.io/scaleio`
* `gateway`: address to a ScaleIO API gateway (required)
* `system`: the name of the ScaleIO system (required)
* `protectionDomain`: the name of the ScaleIO protection domain
* `storagePool`: the name of the volume storage pool
* `protectionDomain`: the name of the ScaleIO protection domain (required)
* `storagePool`: the name of the volume storage pool (required)
* `storageMode`: the storage provision mode: `ThinProvisionned` (default) or `ThickProvisionned`
* `secretRef`: reference to a configured Secret object (required, see detail below)
* `readOnly`: specifies the access mode to the mounted volume
* `fsType`: the file system to use for the volume
* `secretRef`: reference to a configured Secret object (required)
* `readOnly`: specifies the access mode to the mounted volume (default false)
* `fsType`: the file system to use for the volume (default ext4)
The ScaleIO Kubernetes volume plugin requires a configured Secret object.
The secret must be created with type `kubernetes.io/scaleio` and use the same namespace value as that of the PVC where it is referenced
docs/concepts/storage/volumes.md
+85 -10
View File
@@ -141,7 +141,7 @@ spec:
### hostPath
A `hostPath` volume mounts a file or directory from the host node's filesystem
into your pod. This is not something that most Pods will need, but it offers a
into your pod. This is not something that most Pods will need, but it offers a
powerful escape hatch for some applications.
For example, some uses for a `hostPath` are:
@@ -149,6 +149,24 @@ For example, some uses for a `hostPath` are:
* running a container that needs access to Docker internals; use a `hostPath`
of `/var/lib/docker`
* running cAdvisor in a container; use a `hostPath` of `/dev/cgroups`
* allowing a pod to specify whether a given hostPath should exist prior to the
pod running, whether it should be created, and what it should exist as
In addition to the required `path` property, user can optionally specify a `type` for a `hostPath` volume.
The supported values for field `type` are:
| Value | Behavior |
|:------|:---------|
| | Empty string (default) is for backward compatibility, which means that no checks will be performed before mounting the hostPath volume. |
| `DirectoryOrCreate` | If nothing exists at the given path, an empty directory will be created there as needed with permission set to 0755, having the same group and ownership with Kubelet. |
| `Directory` | A directory must exist at the given path |
| `FileOrCreate` | If nothing exists at the given path, an empty file will be created there as needed with permission set to 0644, having the same group and ownership with Kubelet. |
| `File` | A file must exist at the given path |
| `Socket` | A UNIX socket must exist at the given path |
| `CharDevice` | A character device must exist at the given path |
| `BlockDevice` | A block device must exist at the given path |
Watch out when using this type of volume, because:
@@ -156,7 +174,7 @@ Watch out when using this type of volume, because:
behave differently on different nodes due to different files on the nodes
* when Kubernetes adds resource-aware scheduling, as is planned, it will not be
able to account for resources used by a `hostPath`
* the directories created on the underlying hosts are only writable by root. You
* the files or directories created on the underlying hosts are only writable by root. You
either need to run your process as root in a
[privileged container](/docs/user-guide/security-context) or modify the file
permissions on the host to be able to write to a `hostPath` volume
@@ -180,6 +198,8 @@ spec:
hostPath:
# directory location on host
path: /data
# this field is optional
type: Directory
```
### gcePersistentDisk
@@ -549,14 +569,6 @@ with ConfigMap naming.
volume source. However, as illustrated above, you can explicitly set the `mode`
for each individual projection.
### FlexVolume
A `FlexVolume` enables users to mount vendor volumes into a pod. It expects vendor
drivers are installed in the volume plugin path on each kubelet node. This is
an alpha feature and may change in future.
More details are in [here](https://github.com/kubernetes/examples/tree/{{page.githubbranch}}/staging/volumes/flexvolume/README.md).
### AzureFileVolume
A `AzureFileVolume` is used to mount a Microsoft Azure File Volume (SMB 2.1 and 3.0)
@@ -699,6 +711,8 @@ spec:
scaleIO:
gateway: https://localhost:443/api
system: scaleio
protectionDomain: sd0
storagePool: sp1
volumeName: vol-0
secretRef:
name: sio-secret
@@ -847,6 +861,67 @@ request a certain amount of space using a [resource](/docs/user-guide/compute-re
specification, and to select the type of media to use, for clusters that have
several media types.
## Out-of-Tree Volume Plugins
In addition to the previously listed volume types, storage vendors may create
custom plugins without adding it to the Kubernetes repository. This can be
achieved by using the `FlexVolume` plugin.
`FlexVolume` enables users to mount vendor volumes into a pod. The vendor plugin
is implemented using a driver, an executable supporting a list of volume commands
defined by the `FlexVolume` API. Drivers must be installed in a pre-defined
volume plugin path on each node. This is an alpha feature and may change in future.
More details can be found [here](https://github.com/kubernetes/community/blob/master/contributors/devel/flexvolume.md).
## Mount propagation
**Note:** Mount propagation is an alpha feature in Kubernetes 1.8 and may be
redesigned or even removed in future releases.
{: .note}
Mount propagation allows for sharing volumes mounted by a Container to
other Containers in the same Pod, or even to other Pods on the same node.
If the MountPropagation feature is disabled, volume mounts in pods are not propagated.
That is, Containers run with `private` mount propagation as described in the
[Linux kernel documentation](https://www.kernel.org/doc/Documentation/filesystems/sharedsubtree.txt).
To enable this feature, specify `MountPropagation=true` in the
`--feature-gates` command line option. When enabled, the `volumeMounts` field
of a Container has a new `mountPropagation` subfield. Its values are:
* `HostToContainer` - This volume mount will receive all subsequent mounts
that are mounted to this volume or any of its subdirectories. This is
the default mode when the MountPropagation feature is enabled.
In other words, if the host mounts anything inside the volume mount, the
Container will see it mounted there.
Similarly, if any pod with `Bidirectional` mount propagation to the same
volume mounts anything there, the Container with `HostToContainer` mount
propagation will see it.
This mode is equal to `rslave` mount propagation as described in the
[Linux kernel documentation](https://www.kernel.org/doc/Documentation/filesystems/sharedsubtree.txt)
* `Bidirectional` - This volume mount behaves the same the `HostToContainer` mount.
In addition, all volume mounts created by the Container will be propagated
back to the host and to all Containers of all Pods that use the same volume.
A typical use case for this mode is a Pod with a Flex volume driver or
a Pod that needs to mount something on the host using a HostPath volume.
This mode is equal to `rshared` mount propagation as described in the
[Linux kernel documentation](https://www.kernel.org/doc/Documentation/filesystems/sharedsubtree.txt)
**Caution:** `Bidirectional` mount propagation can be dangerous. It can damage
the host operating system and therefore it is allowed only in privileged
Containers. Familiarity with Linux kernel behavior is strongly recommended.
In addition, any volume mounts created by Containers in Pods must be destroyed
(unmounted) by the Containers on termination.
{: .caution}
{% endcapture %}
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