Split PodPreset concept out from task doc (#5984)
Qiming
Steve Perry
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@ -40,6 +40,7 @@ toc:
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- docs/concepts/workloads/pods/pod.md
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- docs/concepts/workloads/pods/pod-lifecycle.md
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- docs/concepts/workloads/pods/init-containers.md
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- docs/concepts/workloads/pods/podpreset.md
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- docs/concepts/workloads/pods/disruptions.md
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- title: Controllers
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section:
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@ -364,7 +364,8 @@ For more information about persistent volume claims, see ["PersistentVolumeClaim
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### PodPreset
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This plug-in injects a pod with the fields specified in a matching PodPreset.
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See also [Inject Information into Pods Using a PodPreset](/docs/tasks/inject-data-application/podpreset)
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See also [PodPreset concept](docs/concepts/workloads/pods/podpreset/) and
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[Inject Information into Pods Using a PodPreset](/docs/tasks/inject-data-application/podpreset)
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for more information.
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### PodSecurityPolicy
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@ -0,0 +1,79 @@
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---
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approvers:
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- jessfraz
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title: Pod Preset
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---
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{% capture overview %}
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This page provides an overview of PodPresets, which are objects for injecting
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certain information into pods at creation time. The information can include
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secrets, volumes, volume mounts, and environment variables.
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{% endcapture %}
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{:toc}
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{% capture body %}
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## Understanding Pod Presets
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A "Pod Preset" is an API resource for injecting additional runtime requirements
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into a Pod at creation time.
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You use [label selectors] (/docs/concepts/overview/working-with-objects/labels/#label-selectors)
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to specify the Pods to which a given Pod Preset applies.
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Using a Pod Preset allows pod template authors to not have to explicitly provide
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all information for every pod. This way, authors of pod templates consuming a
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specific service do not need to know all the details about that service.
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For more information about the background, see the [design proposal for PodPreset](https://git.k8s.io/community/contributors/design-proposals/service-catalog/pod-preset.md).
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## How It Works
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Kubernetes provides an admission controller (`PodPreset`) which, when enabled,
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applies Pod Presets to incoming pod creation requests.
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When a pod creation request occurs, the system does the following:
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1. Retrieve all `PodPresets` available for use.
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1. Check if the label selectors of any `PodPreset` matches the labels on the
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pod being created.
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1. Attempt to merge the various resources defined by the `PodPreset` into the
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Pod being created.
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1. On error, throw an event documenting the merge error on the pod, and create
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the pod _without_ any injected resources from the `PodPreset`.
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1. Annotate the resulting mmodified Pod spec to indicate that it has been
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modified by a `PodPreset`. The annotation is of the form
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`podpreset.admission.kubernetes.io/podpreset-<pod-preset name>": "<resource version>"`.
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Each Pod can be matched zero or more Pod Presets; and each `PodPreset` can be
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applied to zero or more pods. When a `PodPreset` is applied to one or more
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Pods, Kubernetes modifies the Pod Spec. For changes to `Env`, `EnvFrom`, and
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`VolumeMounts`, Kubernetes modifies the container spec for all containers in
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the Pod; for changes to `Volume`, Kubernetes modifies the Pod Spec.
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### Disable Pod Preset for a Specific Pod
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There may be instances where you wish for a Pod to not be altered by any Pod
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Preset mutations. In these cases, you can add an annotation in the Pod Spec
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of the form: `podpreset.admission.kubernetes.io/exclude: "true"`.
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## Enable Pod Preset
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In order to use Pod Presets in your cluster you must ensure the following:
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1. You have enabled the API type `settings.k8s.io/v1alpha1/podpreset`. For
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example, this can be done by including `settings.k8s.io/v1alpha1=true` in
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the `--runtime-config` option for the API server.
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1. You have enabled the admission controller `PodPreset`. One way to doing this
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is to include `PodPreset` in the `--admission-control` option value specified
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for the API server.
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1. You have defined your Pod Presets by creating `PodPreset` objects in the
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namespace you will use.
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{% endcapture %}
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{% capture whatsnext %}
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* [Injecting data into a Pod using PodPreset](/docs/tasks/inject-data-application/podpreset/)
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{% endcapture %}
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{% include templates/concept.md %}
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@ -4,66 +4,15 @@ approvers:
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title: Inject Information into Pods Using a PodPreset
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---
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You can use a `podpreset` object to inject certain information into pods at creation
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time. This information can include secrets, volumes, volume mounts, and environment
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variables.
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See [PodPreset proposal](https://git.k8s.io/community/contributors/design-proposals/service-catalog/pod-preset.md) for more information.
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You can use a `podpreset` object to inject information like secrets, volume
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mounts, and environment variables etc into pods at creation time.
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This task shows some examples on using the `PodPreset` resource.
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You can get an overview of PodPresets at
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[Understanding Pod Presets](/docs/concepts/workloads/pods/podpreset/).
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* TOC
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{:toc}
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## What is a Pod Preset?
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A _Pod Preset_ is an API resource that you can use to inject additional runtime
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requirements into a Pod at creation time. You use label selectors to specify
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the Pods to which a given Pod Preset applies. Check out more information on [label
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selectors](/docs/concepts/overview/working-with-objects/labels/#label-selectors).
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Using a Pod Preset allows pod template authors to not have to explicitly set
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information for every pod. This way, authors of pod templates consuming a
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specific service do not need to know all the details about that service.
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## Admission Control
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_Admission control_ is how Kubernetes applies Pod Presets to incoming pod
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creation requests. When a pod creation request occurs, the system does the
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following:
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1. Retrieve all `PodPresets` available for use.
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1. Match the label selector of the `PodPreset` to the pod being created.
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1. Attempt to merge the various defined resources for the `PodPreset` into the
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Pod being created.
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1. On error, throw an event documenting the merge error on the pod, and create
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the pod _without_ any injected resources from the `PodPreset`.
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### Behavior
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When a `PodPreset` is applied to one or more Pods, Kubernetes modifies the pod
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spec. For changes to `Env`, `EnvFrom`, and `VolumeMounts`, Kubernetes modifies
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the container spec for all containers in the Pod; for changes to Volume,
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Kubernetes modifies the Pod Spec.
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Kubernetes annotates the resulting modified pod spec to show that it was
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modified by a `PodPreset`. The annotation is of the form
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`podpreset.admission.kubernetes.io/podpreset-<pod-preset name>": "<resource version>"`.
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## Enable Pod Preset
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In order to use Pod Presets in your cluster you must ensure the
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following
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1. You have enabled the api type `settings.k8s.io/v1alpha1/podpreset`
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1. You have enabled the admission controller `PodPreset`
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1. You have defined your pod presets
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## Disable Pod Preset for a pod
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There may be instances where you wish for a pod to not be altered by any pod
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preset mutations. For these events, one can add an annotation in the pod spec
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of the form: `podpreset.admission.kubernetes.io/exclude: "true"`.
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## Create a Pod Preset
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### Simple Pod Spec Example
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