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

reviewers	title
jessfraz	Inject Information into Pods Using a PodPreset

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. You can get an overview of PodPresets at Understanding Pod Presets.

{{< toc >}}

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.

{{< code file="podpreset-preset.yaml" >}}

Create the PodPreset:

kubectl create -f https://k8s.io/docs/tasks/inject-data-application/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.

{{< code file="podpreset-pod.yaml" >}}

Create a pod:

$ kubectl create -f https://k8s.io/docs/tasks/inject-data-application/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:

{{< code 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:

{{< code file="podpreset-pod.yaml" >}}

User submitted ConfigMap:

{{< code file="podpreset-configmap.yaml" >}}

Example Pod Preset:

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

Pod spec after admission controller:

{{< code 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:

{{< code file="podpreset-replicaset.yaml" >}}

Example Pod Preset:

{{< code 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.

{{< code 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:

{{< code file="podpreset-pod.yaml" >}}

Example Pod Preset:

{{< code file="podpreset-preset.yaml" >}}

Another Pod Preset:

{{< code file="podpreset-proxy.yaml" >}}

Pod spec after admission controller:

{{< code 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:

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

Example Pod Preset:

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

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

{{< code 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