Customizing Pods

Motivation

It is common for users to customize their Applications for specific environments. Simple customizations to Pod Templates may be through Images, Environment Variables and Command Line Arguments.

Common examples include:

Running different versions of an Image for dev, test, canary, production
Configuring different Pod Environment Variables and Arguments for dev, test, canary, production

Reference

Customizing Images

Use Case: Different Environments (test, dev, staging, canary, prod) use images with different tags.

Override the name or tag for an image field from a Pod Template in a base by specifying the images field in the kustomization.yaml.

Field	Description	Example Field	Example Result
`name`	Match images with this image name	`name: nginx`
`newTag`	Override the image tag or digest for images whose image name matches `name`	`newTag: new`	`nginx:old` -> `nginx:new`
`newName`	Override the image name for images whose image name matches `name`	`newName: nginx-special`	`nginx:old` -> `nginx-special:old`

Input: The kustomization.yaml file

# kustomization.yaml
bases:
- ../base
images:
  - name: nginx-pod
    newTag: 1.15
    newName: nginx-pod-2

Base: Resources to be modified by the kustomization.yaml

# ../base/kustomization.yaml
resources:
- deployment.yaml

# ../base/deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx-pod

Applied: The Resource that is Applied to the cluster

# Modified Base Resource
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: nginx
  name: nginx-deployment
spec:
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      # The image image tag has been changed for the container
      - name: nginx
        image: nginx-pod-2:1.15

Replacing Images

newName allows an image name to be replaced with another arbitrary image name. e.g. you could call your image webserver or database and replace it with nginx or mysql.

For more information on customizing images, see Container Images.

Customizing Pod Environment Variables

Use Case: Different Environments (test, dev, staging, canary, prod) are configured with different Environment Variables.

Override Pod Environment Variables.

Base uses ConfigMap data in Pods as Environment Variables
Each Variant overrides or extends ConfigMap data

Input: The kustomization.yaml file

# kustomization.yaml
bases:
- ../base
configMapGenerator:
- name: special-config
  behavior: merge
  literals:
  - special.how=very # override the base value
  - special.type=charm # add a value to the base

Base: kustomization.yaml and Resources

# ../base/kustomization.yaml
resources:
- deployment.yaml
configMapGenerator:
- name: special-config
  behavior: merge
  literals:
  - special.how=some # this value is overridden
  - special.other=that # this value is added

# ../base/deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx
        envFrom:
        - configMapRef:
            name: special-config

Applied: The Resources that are Applied to the cluster

# Generated Variant Resource
apiVersion: v1
kind: ConfigMap
metadata:
  name: special-config-82tc88cmcg
data:
  special.how: very
  special.type: charm
  special.other: that
---
# Unmodified Base Resource
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: nginx
  name: nginx-deployment
spec:
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx
        envFrom:
        # Container env will have the overridden ConfigMap values
        - configMapRef:
            name: special-config-82tc88cmcg

See ConfigMaps and Secrets.

Customizing Pod Command Arguments

Use Case: Different Environments (test, dev, staging, canary, prod) provide different Commandline Arguments to a Pod.

Override Pod Command Arguments.

Base uses ConfigMap data in Pods as Command Arguments
Each Variant defines different ConfigMap data

Input: The kustomization.yaml file

# kustomization.yaml
bases:
- ../base
configMapGenerator:
- name: special-config
  behavior: merge
  literals:
  - SPECIAL_LEVEL=very
  - SPECIAL_TYPE=charm

# ../base/kustomization.yaml
resources:
- deployment.yaml

configMapGenerator:
- name: special-config
  literals:
  - SPECIAL_LEVEL=override.me
  - SPECIAL_TYPE=override.me

# ../base/deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: test-container
        image: k8s.gcr.io/busybox
        command: [ "/bin/sh" ]
        # Use the ConfigMap Environment Variables in the Command
        args: ["-c", "echo $(SPECIAL_LEVEL_KEY) $(SPECIAL_TYPE_KEY)" ]
        env:
          - name: SPECIAL_LEVEL_KEY
            valueFrom:
              configMapKeyRef:
                name: special-config
                key: SPECIAL_LEVEL
          - name: SPECIAL_TYPE_KEY
            valueFrom:
              configMapKeyRef:
                name: special-config
                key: SPECIAL_TYPE

Applied: The Resources that are Applied to the cluster

# Generated Variant Resource
apiVersion: v1
kind: ConfigMap
metadata:
  name: special-config-82tc88cmcg
data:
  SPECIAL_LEVEL: very
  SPECIAL_TYPE: charm
---
# Unmodified Base Resource
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: nginx
  name: nginx-deployment
spec:
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - image: k8s.gcr.io/busybox
        name: test-container
        command:
        - /bin/sh
        args:
        - -c
        # Container args will have the overridden ConfigMap values
        - echo $(SPECIAL_LEVEL_KEY) $(SPECIAL_TYPE_KEY)
        env:
        - name: SPECIAL_LEVEL_KEY
          valueFrom:
            configMapKeyRef:
              key: SPECIAL_LEVEL
              name: special-config-82tc88cmcg
        - name: SPECIAL_TYPE_KEY
          valueFrom:
            configMapKeyRef:
              key: SPECIAL_TYPE
              name: special-config-82tc88cmcg

More Info

See Secrets and ConfigMaps for more information on ConfigMap and Secret generation.

Customizing Pod Templates

Customizing Pods

Motivation

Customizing Images

Customizing Pod Environment Variables

Customizing Pod Command Arguments

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