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Docs for KEP 2200
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* Document DenyServiceExternalIPs admission controller
* Re-order other admission controller blocks to be alphabetical
* Document DefaultIngressClass (missing)
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thockin committed Jan 29, 2021
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122 changes: 75 additions & 47 deletions content/en/docs/reference/access-authn-authz/admission-controllers.md
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Expand Up @@ -94,7 +94,7 @@ kube-apiserver -h | grep enable-admission-plugins
In the current version, the default ones are:

```shell
NamespaceLifecycle, LimitRanger, ServiceAccount, TaintNodesByCondition, Priority, DefaultTolerationSeconds, DefaultStorageClass, StorageObjectInUseProtection, PersistentVolumeClaimResize, RuntimeClass, CertificateApproval, CertificateSigning, CertificateSubjectRestriction, DefaultIngressClass, MutatingAdmissionWebhook, ValidatingAdmissionWebhook, ResourceQuota
AlwaysAdmit, AlwaysDeny, AlwaysPullImages, CertificateApproval, CertificateSigning, CertificateSubjectRestriction, DefaultIngressClass, DefaultStorageClass, DefaultTolerationSeconds, DenyEscalatingExec, DenyExecOnPrivileged, DenyServiceExternalIPs, EventRateLimit, ExtendedResourceToleration, ImagePolicyWebhook, LimitPodHardAntiAffinityTopology, LimitRanger, MutatingAdmissionWebhook, NamespaceAutoProvision, NamespaceExists, NamespaceLifecycle, NodeRestriction, OwnerReferencesPermissionEnforcement, PersistentVolumeClaimResize, PersistentVolumeLabel, PodNodeSelector, PodSecurityPolicy, PodTolerationRestriction, Priority, ResourceQuota, RuntimeClass, SecurityContextDeny, ServiceAccount, StorageObjectInUseProtection, TaintNodesByCondition, ValidatingAdmissionWebhook
```

## What does each admission controller do?
Expand All @@ -105,6 +105,12 @@ NamespaceLifecycle, LimitRanger, ServiceAccount, TaintNodesByCondition, Priority

This admission controller allows all pods into the cluster. It is deprecated because its behavior is the same as if there were no admission controller at all.

### AlwaysDeny {#alwaysdeny}

{{< feature-state for_k8s_version="v1.13" state="deprecated" >}}

Rejects all requests. AlwaysDeny is DEPRECATED as no real meaning.

### AlwaysPullImages {#alwayspullimages}

This admission controller modifies every new Pod to force the image pull policy to Always. This is useful in a
Expand All @@ -115,12 +121,6 @@ scheduled onto the right node), without any authorization check against the imag
is enabled, images are always pulled prior to starting containers, which means valid credentials are
required.

### AlwaysDeny {#alwaysdeny}

{{< feature-state for_k8s_version="v1.13" state="deprecated" >}}

Rejects all requests. AlwaysDeny is DEPRECATED as no real meaning.

### CertificateApproval {#certificateapproval}

This admission controller observes requests to 'approve' CertificateSigningRequest resources and performs additional
Expand All @@ -145,6 +145,22 @@ This admission controller observes creation of CertificateSigningRequest resourc
of `kubernetes.io/kube-apiserver-client`. It rejects any request that specifies a 'group' (or 'organization attribute')
of `system:masters`.

### DefaultIngressClass {#defaultingressclass}

This admission controller observes creation of `Ingress` objects that do not request any specific
ingress class and automatically adds a default ingress class to them. This way, users that do not
request any special ingress class do not need to care about them at all and they will get the
default one.

This admission controller does not do anything when no default ingress class is configured. When more than one ingress
class is marked as default, it rejects any creation of `Ingress` with an error and an administrator
must revisit their `IngressClass` objects and mark only one as default (with the annotation
"ingressclass.kubernetes.io/is-default-class"). This admission controller ignores any `Ingress`
updates; it acts only on creation.

See [ingress](/docs/concepts/services-networking/ingress/) documentation for more about ingress
classes and how to mark one as default.

### DefaultStorageClass {#defaultstorageclass}

This admission controller observes creation of `PersistentVolumeClaim` objects that do not request any specific storage class
Expand All @@ -169,33 +185,45 @@ have toleration for taints `node.kubernetes.io/not-ready:NoExecute` or
`node.kubernetes.io/unreachable:NoExecute`.
The default value for `default-not-ready-toleration-seconds` and `default-unreachable-toleration-seconds` is 5 minutes.

### DenyExecOnPrivileged {#denyexeconprivileged}
### DenyEscalatingExec {#denyescalatingexec}

{{< feature-state for_k8s_version="v1.13" state="deprecated" >}}

This admission controller will intercept all requests to exec a command in a pod if that pod has a privileged container.
This admission controller will deny exec and attach commands to pods that run with escalated privileges that
allow host access. This includes pods that run as privileged, have access to the host IPC namespace, and
have access to the host PID namespace.

This functionality has been merged into [DenyEscalatingExec](#denyescalatingexec).
The DenyExecOnPrivileged admission plugin is deprecated and will be removed in v1.18.
The DenyEscalatingExec admission plugin is deprecated and will be removed in v1.18.

Use of a policy-based admission plugin (like [PodSecurityPolicy](#podsecuritypolicy) or a custom admission plugin)
which can be targeted at specific users or Namespaces and also protects against creation of overly privileged Pods
is recommended instead.

### DenyEscalatingExec {#denyescalatingexec}
### DenyExecOnPrivileged {#denyexeconprivileged}

{{< feature-state for_k8s_version="v1.13" state="deprecated" >}}

This admission controller will deny exec and attach commands to pods that run with escalated privileges that
allow host access. This includes pods that run as privileged, have access to the host IPC namespace, and
have access to the host PID namespace.
This admission controller will intercept all requests to exec a command in a pod if that pod has a privileged container.

The DenyEscalatingExec admission plugin is deprecated and will be removed in v1.18.
This functionality has been merged into [DenyEscalatingExec](#denyescalatingexec).
The DenyExecOnPrivileged admission plugin is deprecated and will be removed in v1.18.

Use of a policy-based admission plugin (like [PodSecurityPolicy](#podsecuritypolicy) or a custom admission plugin)
which can be targeted at specific users or Namespaces and also protects against creation of overly privileged Pods
is recommended instead.

### DenyServiceExternalIPs

This admission controller rejects all net-new usage of the `Service` field `externalIPs`. This
feature is very powerful (allows network traffic interception) and not well policied. When enabled,
users of the cluster may not create new Services which use `externalIPs` and may not add new values
to `externalIPs` on existing `Service` objects. Existing uses of `externalIPs` are not affected,
and users may remove values from `externalIPs` on existing `Service` objects.

Most users do not need this feature at all, and cluster admins should consider disabling it.
Clusters that do need to use this feature should consider using some custom policy to manage usage
of it.

### EventRateLimit {#eventratelimit}

{{< feature-state for_k8s_version="v1.13" state="alpha" >}}
Expand Down Expand Up @@ -553,6 +581,37 @@ This admission controller also protects the access to `metadata.ownerReferences[
of an object, so that only users with "update" permission to the `finalizers`
subresource of the referenced *owner* can change it.

### PersistentVolumeClaimResize {#persistentvolumeclaimresize}

This admission controller implements additional validations for checking incoming `PersistentVolumeClaim` resize requests.

{{< note >}}
Support for volume resizing is available as an alpha feature. Admins must set the feature gate `ExpandPersistentVolumes`
to `true` to enable resizing.
{{< /note >}}

After enabling the `ExpandPersistentVolumes` feature gate, enabling the `PersistentVolumeClaimResize` admission
controller is recommended, too. This admission controller prevents resizing of all claims by default unless a claim's `StorageClass`
explicitly enables resizing by setting `allowVolumeExpansion` to `true`.

For example: all `PersistentVolumeClaim`s created from the following `StorageClass` support volume expansion:

```yaml
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
name: gluster-vol-default
provisioner: kubernetes.io/glusterfs
parameters:
resturl: "http://192.168.10.100:8080"
restuser: ""
secretNamespace: ""
secretName: ""
allowVolumeExpansion: true
```

For more information about persistent volume claims, see [PersistentVolumeClaims](/docs/concepts/storage/persistent-volumes/#persistentvolumeclaims).

### PersistentVolumeLabel {#persistentvolumelabel}

{{< feature-state for_k8s_version="v1.13" state="deprecated" >}}
Expand Down Expand Up @@ -638,37 +697,6 @@ PodNodeSelector allows forcing pods to run on specifically labeled nodes. Also s
admission plugin, which allows preventing pods from running on specifically tainted nodes.
{{< /note >}}

### PersistentVolumeClaimResize {#persistentvolumeclaimresize}

This admission controller implements additional validations for checking incoming `PersistentVolumeClaim` resize requests.

{{< note >}}
Support for volume resizing is available as an alpha feature. Admins must set the feature gate `ExpandPersistentVolumes`
to `true` to enable resizing.
{{< /note >}}

After enabling the `ExpandPersistentVolumes` feature gate, enabling the `PersistentVolumeClaimResize` admission
controller is recommended, too. This admission controller prevents resizing of all claims by default unless a claim's `StorageClass`
explicitly enables resizing by setting `allowVolumeExpansion` to `true`.

For example: all `PersistentVolumeClaim`s created from the following `StorageClass` support volume expansion:

```yaml
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
name: gluster-vol-default
provisioner: kubernetes.io/glusterfs
parameters:
resturl: "http://192.168.10.100:8080"
restuser: ""
secretNamespace: ""
secretName: ""
allowVolumeExpansion: true
```

For more information about persistent volume claims, see [PersistentVolumeClaims](/docs/concepts/storage/persistent-volumes/#persistentvolumeclaims).

### PodSecurityPolicy {#podsecuritypolicy}

This admission controller acts on creation and modification of the pod and determines if it should be admitted
Expand Down
2 changes: 1 addition & 1 deletion content/en/docs/reference/command-line-tools-reference/kube-apiserver.md
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Expand Up @@ -470,7 +470,7 @@ kube-apiserver [flags]
<td colspan="2">--enable-admission-plugins stringSlice</td>
</tr>
<tr>
<td></td><td style="line-height: 130%; word-wrap: break-word;">admission plugins that should be enabled in addition to default enabled ones (NamespaceLifecycle, LimitRanger, ServiceAccount, TaintNodesByCondition, Priority, DefaultTolerationSeconds, DefaultStorageClass, StorageObjectInUseProtection, PersistentVolumeClaimResize, RuntimeClass, CertificateApproval, CertificateSigning, CertificateSubjectRestriction, DefaultIngressClass, MutatingAdmissionWebhook, ValidatingAdmissionWebhook, ResourceQuota). Comma-delimited list of admission plugins: AlwaysAdmit, AlwaysDeny, AlwaysPullImages, CertificateApproval, CertificateSigning, CertificateSubjectRestriction, DefaultIngressClass, DefaultStorageClass, DefaultTolerationSeconds, DenyEscalatingExec, DenyExecOnPrivileged, EventRateLimit, ExtendedResourceToleration, ImagePolicyWebhook, LimitPodHardAntiAffinityTopology, LimitRanger, MutatingAdmissionWebhook, NamespaceAutoProvision, NamespaceExists, NamespaceLifecycle, NodeRestriction, OwnerReferencesPermissionEnforcement, PersistentVolumeClaimResize, PersistentVolumeLabel, PodNodeSelector, PodSecurityPolicy, PodTolerationRestriction, Priority, ResourceQuota, RuntimeClass, SecurityContextDeny, ServiceAccount, StorageObjectInUseProtection, TaintNodesByCondition, ValidatingAdmissionWebhook. The order of plugins in this flag does not matter.</td>
<td></td><td style="line-height: 130%; word-wrap: break-word;">admission plugins that should be enabled in addition to default enabled ones (NamespaceLifecycle, LimitRanger, ServiceAccount, TaintNodesByCondition, Priority, DefaultTolerationSeconds, DefaultStorageClass, StorageObjectInUseProtection, PersistentVolumeClaimResize, RuntimeClass, CertificateApproval, CertificateSigning, CertificateSubjectRestriction, DefaultIngressClass, MutatingAdmissionWebhook, ValidatingAdmissionWebhook, ResourceQuota). Comma-delimited list of admission plugins: AlwaysAdmit, AlwaysDeny, AlwaysPullImages, CertificateApproval, CertificateSigning, CertificateSubjectRestriction, DefaultIngressClass, DefaultStorageClass, DefaultTolerationSeconds, DenyEscalatingExec, DenyExecOnPrivileged, DenyServiceExternalIPs, EventRateLimit, ExtendedResourceToleration, ImagePolicyWebhook, LimitPodHardAntiAffinityTopology, LimitRanger, MutatingAdmissionWebhook, NamespaceAutoProvision, NamespaceExists, NamespaceLifecycle, NodeRestriction, OwnerReferencesPermissionEnforcement, PersistentVolumeClaimResize, PersistentVolumeLabel, PodNodeSelector, PodSecurityPolicy, PodTolerationRestriction, Priority, ResourceQuota, RuntimeClass, SecurityContextDeny, ServiceAccount, StorageObjectInUseProtection, TaintNodesByCondition, ValidatingAdmissionWebhook. The order of plugins in this flag does not matter.</td>
</tr>

<tr>
Expand Down

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