Injecting Information into Pods Using Pod Presets

You are viewing documentation for a release that is no longer supported. The latest supported version of version 3 is [3.11]. For the most recent version 4, see [4]

You are viewing documentation for a release that is no longer supported. The latest supported version of version 3 is [3.11]. For the most recent version 4, see [4]

Overview

A pod preset is an object that injects user-specified information into pods as they are created.

Using pod preset objects you can inject:

• secret objects

• ConfigMap objects

• storage volumes

• container volume mounts

• environment variables

Developers only need make sure the pod labels match the label selector on the PodPreset in order to add all that information to the pod. The label on a pod associates the pod with one or more pod preset objects that have a matching label selectors.

Using pod presets, a developer can provision pods without needing to know the details about the services the pod will consume. An administrator can keep configuration items of a service invisible from a developer without preventing the developer from deploying pods. For example, an administrator can create a pod preset that provides the name, user name, and password for a database through a secret and the database port through environment variables. The pod developer only needs to know the label to use to include all the information in pods. A developer can also create pod presets and perform all the same tasks. For example, the developer can create a preset that injects environment variable automatically into multiple pods.

When a pod preset is applied to a pod, OKD modifies the pod specification, adding the injectable data and annotating the pod spec to show that it was modified by a pod preset. The annotation is of the form:

podpreset.admission.kubernetes.io/<pod-preset name>: `resource version`

In order to use pod presets in your cluster:

• An administrator must enable the pod preset admission controller plug-in through the /etc/origin/master/master-config.yaml;

• The pod preset author must enable the API type settings.k8s.io/v1alpha1/podpreset through the pod preset and add injectable information to the pod preset.

If the pod creation encounters an error, the pod is created without any injected resources from the pod preset.

You can exclude specific pods from being altered by any pod preset mutations using the podpreset.admission.kubernetes.io/exclude: "true" parameter in the pod specification. See the example pod specification below.

Sample pod preset object

kind: PodPreset
apiVersion: settings.k8s.io/v1alpha1 (1)
metadata:
  name: allow-database (2)
spec:
  selector:
    matchLabels:
      role: frontend (3)
  env:
    - name: DB_PORT (4)
      value: "6379" (4)
  envFrom:
    - configMapRef: (5)
      name: etcd-env-config
    - secretKeyRef: (6)
      name: test-secret
  volumeMounts: (7)
    - mountPath: /cache
      name: cache-volume
  volumes: (8)
    - name: cache-volume
      emptyDir: {}

Sample pod specification

apiVersion: v1
kind: Pod
metadata:
  name: website
  labels:
    app: website
    role: frontend (1)
spec:
  containers:
    - name: website
      image: ecorp/website
      ports:
        - containerPort: 80

Sample pod specification after a pod preset

apiVersion: v1
kind: Pod
metadata:
  name: website
  labels:
    app: website
    role: frontend
  annotations:
    podpreset.admission.kubernetes.io/allow-database: "resource version" (1)
spec:
  containers:
    - name: website
      image: ecorp/website
      volumeMounts: (2)
        - mountPath: /cache
          name: cache-volume
      ports:
        - containerPort: 80
      env: (3)
        - name: DB_PORT
          value: "6379"
      envFrom: (4)
        - configMapRef:
          name: etcd-env-config
        - secretKeyRef:
          name: test-secret
  volumes: (5)
    - name: cache-volume
      emptyDir: {}

Sample pod specification to exclude the pod from pod preset

apiVersion: v1
kind: Pod
metadata:
  name: no-podpreset
  labels:
    app: website
    role: frontend
  annotations:
    podpreset.admission.kubernetes.io/exclude: "true" (1)
spec:
  containers:
    - name: hello-pod
      image: docker.io/ocpqe/hello-pod

Creating Pod Presets

The following example demonstrates how to create and use pod presets.

Add the Admission Controller

An administrator can check the /etc/origin/master/master-config.yaml file to make sure the pod preset admission controller plug-in is present. If the admission controller is not present, add the plug-in using the following:

admissionConfig:
  pluginConfig:
    PodPreset:
      configuration:
        kind: DefaultAdmissionConfig
        apiVersion: v1
        disable: false

Then, restart the OKD services:

# master-restart api
# master-restart controllers

Create the Pod Preset

An administrator or developer creates the pod preset with the settings.k8s.io/v1alpha1 API, the information to inject, and a label selector to match with the pods:

kind: PodPreset
apiVersion: settings.k8s.io/v1alpha1
metadata:
  name: allow-database
spec:
  selector:
    matchLabels:
      role: frontend
  env:
    - name: DB_PORT
      value: "6379"
  volumeMounts:
    - mountPath: /cache
      name: cache-volume
  volumes:
    - name: cache-volume
      emptyDir: {}

Create the Pod

The developer creates the pod with a label that matches the label selector in the pod preset:

1. Create a standard pod specification with a label that matches the label selector in the pod preset:

   apiVersion: v1
   kind: Pod
   metadata:
     name: website
     labels:
       app: website
       role: frontend
   spec:
     containers:
       - name: website
         image: ecorp/website
         ports:
           - containerPort: 80

2. Create the pod:

   $ oc create -f pod.yaml

3. Check the pod spec after creation:

   $ oc get pod website -o yaml
   apiVersion: v1
   kind: Pod
   metadata:
     name: website
     labels:
       app: website
       role: frontend
     annotations:
       podpreset.admission.kubernetes.io/allow-database: "resource version" (1)
   spec:
     containers:
       - name: website
         image: ecorp/website
         volumeMounts: (1)
           - mountPath: /cache
             name: cache-volume
         ports:
           - containerPort: 80
         env: (1)
           - name: DB_PORT
             value: "6379"
     volumes:
       - name: cache-volume
         emptyDir: {}

   1	The annotation is present and the container storage and environment variables are injected.

Using Multiple Pod Presets

You can use multiple pod presets to inject multiple pod injection policies.

• Make sure the pod preset admission controller plug-in is enabled.

• Create a pod preset, similar to the following, with environment variables, mount points, and/or storage volumes:

  kind: PodPreset
  apiVersion: settings.k8s.io/v1alpha1
  metadata:
    name: allow-database
  spec:
    selector:
      matchLabels:
        role: frontend (1)
    env:
      - name: DB_PORT
        value: "6379"
    volumeMounts:
      - mountPath: /cache
        name: cache-volume
    volumes:
      - name: cache-volume
        emptyDir: {}

  1	Label selector to match the pod labels.

• Create a second pod preset, similar to the following:

  kind: PodPreset
  apiVersion: settings.k8s.io/v1alpha1
  metadata:
    name: proxy
  spec:
    selector:
      matchLabels:
        role: frontend (1)
    volumeMounts:
      - mountPath: /etc/proxy/configs
        name: proxy-volume
    volumes:
      - name: proxy-volume
        emptyDir: {}

  1	Label selector to match the pod labels.

• Create a standard pod specification:

  apiVersion: v1
  kind: Pod
  metadata:
    name: website
    labels:
      app: website
      role: frontend (1)
  spec:
    containers:
      - name: website
        image: ecorp/website
        ports:
          - containerPort: 80

  1	Label to match both pod preset label selectors.

• Create the pod:

  $ oc create -f pod.yaml

• Check the pod spec after creation:

  apiVersion: v1
  kind: Pod
  metadata:
    name: website
    labels:
      app: website
      role: frontend
    annotations:
      podpreset.admission.kubernetes.io/allow-database: "resource version" (1)
      podpreset.admission.kubernetes.io/proxy: "resource version" (1)
  spec:
    containers:
      - name: website
        image: ecorp/website
        volumeMounts:
          - mountPath: /cache
            name: cache-volume
          - mountPath: /etc/proxy/configs
            name: proxy-volume
        ports:
          - containerPort: 80
        env:
          - name: DB_PORT
            value: "6379"
    volumes:
      - name: cache-volume
        emptyDir: {}
      - name: proxy-volume
        emptyDir: {}

  1	Annotation indicating that multiple pod presets were injected.

Deleting Pod Presets

You can delete a pod preset using the following command:

$ oc delete podpreset <name>

For example:

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