Kustomize is built into kubectl with -k. Great samples on kubernetes.io/docs

Kustomize provides a template-free way to customize kubernetes manifest

Contents:

In a nutshell provides 3 key features:

  1. generating resources from other sources
  2. setting cross-cutting fields for resources
  3. composing and customizing collections of resources

Generating resources⌗

To generate a ConfigMap from an .env file, add an entry to the envs list in configMapGenerator. Kustomize supports other formats such as .properties.

The .env file:

FOO=Bar

kustomization.yaml:

configMapGenerator:
  - name: example-configmap-1
    envs:
      - .env

Run it:

kubectl kustomize ./

The generated result:

apiVersion: v1
data:
  FOO: Bar
kind: ConfigMap
metadata:
  name: example-configmap-1-42cfbf598f

Setting cross cutting fields⌗

It’s common to set cross-cutting fields for all Kubernetes resources in a project. Some use cases for setting cross-cutting fields:

  • setting the same namespace for all Resources
  • adding the same name prefix or suffix
  • adding the same set of labels
  • adding the same set of annotations

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

kustomization.yaml:

namespace: my-namespace
namePrefix: dev-
nameSuffix: "-001"
commonLabels:
  app: bingo
commonAnnotations:
  oncallPager: 800-555-1212
resources:
  - deployment.yaml

Run it:

kubectl kustomize ./

The generated result:

apiVersion: apps/v1
kind: Deployment
metadata:
  annotations:
    oncallPager: 800-555-1212
  labels:
    app: bingo
  name: dev-nginx-deployment-001
  namespace: my-namespace
spec:
  selector:
    matchLabels:
      app: bingo
  template:
    metadata:
      annotations:
        oncallPager: 800-555-1212
      labels:
        app: bingo
    spec:
      containers:
        - image: nginx
          name: nginx

Composing and customizing resources⌗

Composing⌗

Kustomize supports composition of different resources. The resources field, in the kustomization.yaml file, defines the list of resources to include in a configuration. Here’s an NGINX application comprised of a Deployment and a Service:

kustomization.yaml:

resources:
  - deployment.yaml
  - service.yaml

Customizing⌗

Patches⌗

Kustomize supports different patching mechanisms through patchesStrategicMerge and patchesJson6902. patchesStrategicMerge is a list of file paths. Each file should be resolved to a strategic merge patch. The names inside the patches must match Resource names that are already loaded. Small cohensive patches that do one thing are recommended. For example, create one patch for increasing the deployment replica number and another patch for setting the memory limit.

deployment.yaml:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-nginx
spec:
  selector:
    matchLabels:
      run: my-nginx
  replicas: 2
  template:
    metadata:
      labels:
        run: my-nginx
    spec:
      containers:
        - name: my-nginx
          image: nginx
          ports:
            - containerPort: 80

increase_replicas_patch.yaml:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-nginx
spec:
  replicas: 3

set_memory_patch.yaml.yaml:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-nginx
spec:
  template:
    spec:
      containers:
        - name: my-nginx
          resources:
            limits:
              memory: 512Mi

kustomization.yaml:

resources:
  - deployment.yaml
patchesStrategicMerge:
  - increase_replicas.yaml
  - set_memory.yaml

To apply objects:

kubectl apply -k <directory>/

Images⌗

Container images or injecting field values from other objects into containers without creating patches

kustomization.yaml:

resources:
  - deployment.yaml
images:
  - name: nginx
    newName: my.image.registry/nginx
    newTag: 1.4.0

Replacements⌗

Sometimes the application running in a Pod may need to use configuration values from other objects. For example, a Pod from a Deployment object need to read the Service name from Env or as a command argument. Here we lift the post processed service name and inject it as the 3rd command argument on the pod spec:

kustomization.yaml:

namePrefix: dev-
nameSuffix: "-001"

resources:
  - deployment.yaml
  - service.yaml

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
replacements:
  - source:
      kind: Service
      name: my-nginx
      version: v1
    targets:
      - fieldPaths:
          - spec.template.spec.containers.0.command.2
        select:
          group: apps
          kind: Deployment
          name: my-nginx
          version: v1

Reference⌗

https://kubernetes.io/docs/tasks/manage-kubernetes-objects/kustomization/