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Merge pull request #30366 from aravindhp/windows-projected-volume

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storage: document Windows projected volume limitations
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Kubernetes Prow Robot
2021-11-16 16:11:53 -08:00
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content/en/docs/concepts/storage/projected-volumes.md
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---
reviewers:
- sftim
- marosset
- jsturtevant
- zshihang
title: Projected Volumes
content_type: concept
---
<!-- overview -->
This document describes the current state of _projected volumes_ in Kubernetes. Familiarity with [volumes](/docs/concepts/storage/volumes/) is suggested.
<!-- body -->
## Introduction
A `projected` volume maps several existing volume sources into the same directory.
Currently, the following types of volume sources can be projected:
* [`secret`](/docs/concepts/storage/volumes/#secret)
* [`downwardAPI`](/docs/concepts/storage/volumes/#downwardapi)
* [`configMap`](/docs/concepts/storage/volumes/#configmap)
* `serviceAccountToken`
All sources are required to be in the same namespace as the Pod. For more details,
see the [all-in-one volume design document](https://github.com/kubernetes/community/blob/master/contributors/design-proposals/node/all-in-one-volume.md).
### Example configuration with a secret, a downwardAPI, and a configMap {#example-configuration-secret-downwardapi-configmap}
{{< codenew file="pods/storage/projected-secret-downwardapi-configmap.yaml" >}}
### Example configuration: secrets with a non-default permission mode set {#example-configuration-secrets-nondefault-permission-mode}
{{< codenew file="pods/storage/projected-secrets-nondefault-permission-mode.yaml" >}}
Each projected volume source is listed in the spec under `sources`. The
parameters are nearly the same with two exceptions:
* For secrets, the `secretName` field has been changed to `name` to be consistent
with ConfigMap naming.
* The `defaultMode` can only be specified at the projected level and not for each
volume source. However, as illustrated above, you can explicitly set the `mode`
for each individual projection.
When the `TokenRequestProjection` feature is enabled, you can inject the token
for the current [service account](/docs/reference/access-authn-authz/authentication/#service-account-tokens)
into a Pod at a specified path. For example:
{{< codenew file="pods/storage/projected-service-account-token.yaml" >}}
The example Pod has a projected volume containing the injected service account
token. This token can be used by a Pod's containers to access the Kubernetes API
server. The `audience` field contains the intended audience of the
token. A recipient of the token must identify itself with an identifier specified
in the audience of the token, and otherwise should reject the token. This field
is optional and it defaults to the identifier of the API server.
The `expirationSeconds` is the expected duration of validity of the service account
token. It defaults to 1 hour and must be at least 10 minutes (600 seconds). An administrator
can also limit its maximum value by specifying the `--service-account-max-token-expiration`
option for the API server. The `path` field specifies a relative path to the mount point
of the projected volume.
{{< note >}}
A container using a projected volume source as a [`subPath`](/docs/concepts/storage/volumes/#using-subpath)
volume mount will not receive updates for those volume sources.
{{< /note >}}
## SecurityContext interactions
The [proposal for file permission handling in projected service account volume](https://github.com/kubernetes/enhancements/pull/1598)
enhancement introduced the projected files having the the correct owner
permissions set.
### Linux
In Linux pods that have a projected volume and `RunAsUser` set in the Pod
[`SecurityContext`](/docs/reference/kubernetes-api/workload-resources/pod-v1/#security-context),
the projected files have the correct ownership set including container user
ownership.
### Windows
In Windows pods that have a projected volume and `RunAsUsername` set in the
Pod `SecurityContext`, the ownership is not enforced due to the way user
accounts are managed in Windows. Windows stores and manages local user and group
accounts in a database file called Security Account Manager (SAM). Each
container maintains its own instance of the SAM database, to which the host has
no visibility into while the container is running. Windows containers are
designed to run the user mode portion of the OS in isolation from the host,
hence the maintenance of a virtual SAM database. As a result, the kubelet running
on the host does not have the ability to dynamically configure host file
ownership for virtualized container accounts. It is recommended that if files on
the host machine are to be shared with the container then they should be placed
into their own volume mount outside of `C:\`.
By default, the projected files will have the following ownership as shown for
an example projected volume file:
```powershell
Path : Microsoft.PowerShell.Core\FileSystem::C:\var\run\secrets\kubernetes.io\serviceaccount\..2021_08_31_22_22_18.318230061\ca.crt
Owner : BUILTIN\Administrators
Group : NT AUTHORITY\SYSTEM
Access : NT AUTHORITY\SYSTEM Allow FullControl
BUILTIN\Administrators Allow FullControl
BUILTIN\Users Allow ReadAndExecute, Synchronize
Audit :
Sddl : O:BAG:SYD:AI(A;ID;FA;;;SY)(A;ID;FA;;;BA)(A;ID;0x1200a9;;;BU)
```
This implies all administrator users like `ContainerAdministrator` will have
read, write and execute access while, non-administrator users will have read and
execute access.
{{< note >}}
In general, granting the container access to the host is discouraged as it can
open the door for potential security exploits.
Creating a Windows Pod with `RunAsUser` in it's `SecurityContext` will result in
the Pod being stuck at `ContainerCreating` forever. So it is advised to not use
the Linux only `RunAsUser` option with Windows Pods.
{{< /note >}}
content/en/docs/concepts/storage/volumes.md
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### projected
A `projected` volume maps several existing volume sources into the same directory.
Currently, the following types of volume sources can be projected:
* [`secret`](#secret)
* [`downwardAPI`](#downwardapi)
* [`configMap`](#configmap)
* `serviceAccountToken`
All sources are required to be in the same namespace as the Pod. For more details,
see the [all-in-one volume design document](https://github.com/kubernetes/community/blob/master/contributors/design-proposals/node/all-in-one-volume.md).
#### Example configuration with a secret, a downwardAPI, and a configMap {#example-configuration-secret-downwardapi-configmap}
```yaml
apiVersion: v1
kind: Pod
metadata:
name: volume-test
spec:
containers:
- name: container-test
image: busybox
volumeMounts:
- name: all-in-one
mountPath: "/projected-volume"
readOnly: true
volumes:
- name: all-in-one
projected:
sources:
- secret:
name: mysecret
items:
- key: username
path: my-group/my-username
- downwardAPI:
items:
- path: "labels"
fieldRef:
fieldPath: metadata.labels
- path: "cpu_limit"
resourceFieldRef:
containerName: container-test
resource: limits.cpu
- configMap:
name: myconfigmap
items:
- key: config
path: my-group/my-config
```
#### Example configuration: secrets with a non-default permission mode set {#example-configuration-secrets-nondefault-permission-mode}
```yaml
apiVersion: v1
kind: Pod
metadata:
name: volume-test
spec:
containers:
- name: container-test
image: busybox
volumeMounts:
- name: all-in-one
mountPath: "/projected-volume"
readOnly: true
volumes:
- name: all-in-one
projected:
sources:
- secret:
name: mysecret
items:
- key: username
path: my-group/my-username
- secret:
name: mysecret2
items:
- key: password
path: my-group/my-password
mode: 511
```
Each projected volume source is listed in the spec under `sources`. The
parameters are nearly the same with two exceptions:
* For secrets, the `secretName` field has been changed to `name` to be consistent
with ConfigMap naming.
* The `defaultMode` can only be specified at the projected level and not for each
volume source. However, as illustrated above, you can explicitly set the `mode`
for each individual projection.
When the `TokenRequestProjection` feature is enabled, you can inject the token
for the current [service account](/docs/reference/access-authn-authz/authentication/#service-account-tokens)
into a Pod at a specified path. For example:
```yaml
apiVersion: v1
kind: Pod
metadata:
name: sa-token-test
spec:
containers:
- name: container-test
image: busybox
volumeMounts:
- name: token-vol
mountPath: "/service-account"
readOnly: true
volumes:
- name: token-vol
projected:
sources:
- serviceAccountToken:
audience: api
expirationSeconds: 3600
path: token
```
The example Pod has a projected volume containing the injected service account
token. This token can be used by a Pod's containers to access the Kubernetes API
server. The `audience` field contains the intended audience of the
token. A recipient of the token must identify itself with an identifier specified
in the audience of the token, and otherwise should reject the token. This field
is optional and it defaults to the identifier of the API server.
The `expirationSeconds` is the expected duration of validity of the service account
token. It defaults to 1 hour and must be at least 10 minutes (600 seconds). An administrator
can also limit its maximum value by specifying the `--service-account-max-token-expiration`
option for the API server. The `path` field specifies a relative path to the mount point
of the projected volume.
{{< note >}}
A container using a projected volume source as a [`subPath`](#using-subpath) volume mount will not
receive updates for those volume sources.
{{< /note >}}
A projected volume maps several existing volume sources into the same
directory. For more details, see [projected volumes](/docs/concepts/storage/projected-volumes/)
### quobyte (deprecated) {#quobyte}
content/en/examples/pods/storage/projected-secret-downwardapi-configmap.yaml
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apiVersion: v1
kind: Pod
metadata:
name: volume-test
spec:
containers:
- name: container-test
image: busybox
volumeMounts:
- name: all-in-one
mountPath: "/projected-volume"
readOnly: true
volumes:
- name: all-in-one
projected:
sources:
- secret:
name: mysecret
items:
- key: username
path: my-group/my-username
- downwardAPI:
items:
- path: "labels"
fieldRef:
fieldPath: metadata.labels
- path: "cpu_limit"
resourceFieldRef:
containerName: container-test
resource: limits.cpu
- configMap:
name: myconfigmap
items:
- key: config
path: my-group/my-config
content/en/examples/pods/storage/projected-secrets-nondefault-permission-mode.yaml
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apiVersion: v1
kind: Pod
metadata:
name: volume-test
spec:
containers:
- name: container-test
image: busybox
volumeMounts:
- name: all-in-one
mountPath: "/projected-volume"
readOnly: true
volumes:
- name: all-in-one
projected:
sources:
- secret:
name: mysecret
items:
- key: username
path: my-group/my-username
- secret:
name: mysecret2
items:
- key: password
path: my-group/my-password
mode: 511
content/en/examples/pods/storage/projected-service-account-token.yaml
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apiVersion: v1
kind: Pod
metadata:
name: sa-token-test
spec:
containers:
- name: container-test
image: busybox
volumeMounts:
- name: token-vol
mountPath: "/service-account"
readOnly: true
volumes:
- name: token-vol
projected:
sources:
- serviceAccountToken:
audience: api
expirationSeconds: 3600
path: token