website/content/en/docs/tasks/inject-data-application/podpreset.md

reviewers	title	content_template	weight
jessfraz	Inject Information into Pods Using a PodPreset	templates/task	60

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You can use a podpreset object to inject information like secrets, volume mounts, and environment variables etc into pods at creation time. This task shows some examples on using the PodPreset resource.

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Get an overview of PodPresets at Understanding Pod Presets.

{{< include "task-tutorial-prereqs.md" >}} {{< version-check >}}

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Create a Pod Preset

Simple Pod Spec Example

This is a simple example to show how a Pod spec is modified by the Pod Preset.

{{< codenew file="podpreset/preset.yaml" >}}

Create the PodPreset:

kubectl create -f https://k8s.io/examples/podpreset/preset.yaml

Examine the created PodPreset:

$ kubectl get podpreset
NAME             AGE
allow-database   1m

The new PodPreset will act upon any pod that has label role: frontend.

{{< codenew file="podpreset/pod.yaml" >}}

Create a pod:

$ kubectl create -f https://k8s.io/examples/podpreset/pod.yaml

List the running Pods:

$ kubectl get pods
NAME      READY     STATUS    RESTARTS   AGE
website   1/1       Running   0          4m

Pod spec after admission controller:

{{< codenew file="podpreset/merged.yaml" >}}

To see above output, run the following command:

$ kubectl get pod website -o yaml

Pod Spec with ConfigMap Example

This is an example to show how a Pod spec is modified by the Pod Preset that defines a ConfigMap for Environment Variables.

User submitted pod spec:

{{< codenew file="podpreset/pod.yaml" >}}

User submitted ConfigMap:

{{< codenew file="podpreset/configmap.yaml" >}}

Example Pod Preset:

{{< codenew file="podpreset/allow-db.yaml" >}}

Pod spec after admission controller:

{{< codenew file="podpreset/allow-db-merged.yaml" >}}

ReplicaSet with Pod Spec Example

The following example shows that only the pod spec is modified by the Pod Preset.

User submitted ReplicaSet:

{{< codenew file="podpreset/replicaset.yaml" >}}

Example Pod Preset:

{{< codenew file="podpreset/preset.yaml" >}}

Pod spec after admission controller:

Note that the ReplicaSet spec was not changed, users have to check individual pods to validate that the PodPreset has been applied.

{{< codenew file="podpreset/replicaset-merged.yaml" >}}

Multiple PodPreset Example

This is an example to show how a Pod spec is modified by multiple Pod Injection Policies.

User submitted pod spec:

{{< codenew file="podpreset/pod.yaml" >}}

Example Pod Preset:

{{< codenew file="podpreset/preset.yaml" >}}

Another Pod Preset:

{{< codenew file="podpreset/proxy.yaml" >}}

Pod spec after admission controller:

{{< codenew file="podpreset/multi-merged.yaml" >}}

Conflict Example

This is an example to show how a Pod spec is not modified by the Pod Preset when there is a conflict.

User submitted pod spec:

{{< codenew file="podpreset/conflict-pod.yaml" >}}

Example Pod Preset:

{{< codenew file="podpreset/conflict-preset.yaml" >}}

Pod spec after admission controller will not change because of the conflict:

{{< codenew file="podpreset/conflict-pod.yaml" >}}

If we run kubectl describe... we can see the event:

$ kubectl describe ...
....
Events:
  FirstSeen             LastSeen            Count   From                    SubobjectPath               Reason      Message
  Tue, 07 Feb 2017 16:56:12 -0700   Tue, 07 Feb 2017 16:56:12 -0700 1   {podpreset.admission.kubernetes.io/podpreset-allow-database }    conflict  Conflict on pod preset. Duplicate mountPath /cache.

Deleting a Pod Preset

Once you don't need a pod preset anymore, you can delete it with kubectl:

$ kubectl delete podpreset allow-database
podpreset "allow-database" deleted

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