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In this lesson, you will learn how to use Kustomize transformers to modify Kubernetes configurations. Kustomize supports several built-in transformers, and you can also create custom ones. Here, we focus on a subgroup known as Common Transformers. Imagine you have multiple YAML files such as deployment.yaml and service.yaml. You might want to apply a common configuration—for example, adding a label like “org: KodeKloud” or appending “-dev” to resource names—across all these files. Manually updating each file in a production environment isn’t scalable or efficient. Kustomize transformers offer a systematic way to make consistent changes across all resources. Below are the original Kubernetes resource examples: 
apiVersion: apps/v1
kind: Deployment
metadata:
  name: api-deployment
spec:
  replicas: 1
  selector:
    matchLabels:
      component: api
  template:
    metadata:
      labels:
        component: api
    spec:
      containers:
      - name: nginx
        image: nginx

apiVersion: v1
kind: Service
metadata:
  name: db-service
spec:
  selector:
    component: db-depl
  ports:
  - protocol: "TCP"
    port: 27017
    targetPort: 27017
  type: LoadBalancer
After applying Kustomize transformations, the resources might look like this: 
apiVersion: apps/v1
kind: Deployment
metadata:
  name: api-deployment-dev
spec:
  replicas: 1
  selector:
    matchLabels:
      component: api
      org: KodeKloud
  template:
    metadata:
      labels:
        component: api
        org: KodeKloud
    spec:
      containers:
      - name: nginx
        image: nginx

apiVersion: v1
kind: Service
metadata:
  labels:
    org: KodeKloud
  name: api-service-dev
spec:
  selector:
    component: api
  ports:
  - protocol: "TCP"
    port: 80
    targetPort: 3000
  type: LoadBalancer
Kustomize transformers are essential for ensuring that your Kubernetes configurations remain consistent and manageable across various environments.

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Common Transformation Methods

Below is an overview of common transformations available in Kustomize for managing Kubernetes resources:

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1. Common Label Transformation

This transformer automatically adds the specified labels to all Kubernetes resources. You can define the labels in your kustomization.yaml file as shown below: 
commonLabels:
  org: KodeKloud
For example, a transformed Service resource would appear as: 
apiVersion: v1
kind: Service
metadata:
  labels:
    org: KodeKloud
  name: api-service
spec:
  ports:
  - port: 80
    protocol: TCP
    targetPort: 3000
  selector:
    component: api
  type: LoadBalancer

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2. Namespace Transformation

The namespace transformer assigns all Kubernetes resources to a specified namespace. By specifying the namespace in your kustomization.yaml, all resources will be modified accordingly. For example: 
namespace: lab
After this transformation, a Service resource might look like: 
apiVersion: v1
kind: Service
metadata:
  annotations:
    branch: master
  labels:
    org: KodeKloud
    name: api-service
    namespace: lab
spec:
  ports:
  - port: 80
    protocol: TCP
    targetPort: 3000
  selector:
    component: api
    org: KodeKloud
  type: LoadBalancer
When applying namespace transformations, ensure that the specified namespace exists in your cluster to avoid deployment issues.

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3. Name Prefix and Suffix Transformation

This transformer enables you to systematically add a prefix or suffix to resource names. For instance, to prepend “KodeKloud-” and append “-dev” to each resource name, include the following in your kustomization.yaml: 
namePrefix: KodeKloud-
nameSuffix: -dev
After applying this configuration, a Service resource would be renamed to “KodeKloud-api-service-dev”: 
apiVersion: v1
kind: Service
metadata:
  name: KodeKloud-api-service-dev
spec:
  ports:
  - port: 80
    protocol: TCP
    targetPort: 3000
  selector:
    component: api
  type: LoadBalancer

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4. Common Annotation Transformation

If you need to add specific annotations to all resources, use the common annotations transformer. By setting the annotations in your kustomization.yaml, each resource will automatically include them. For example: 
commonAnnotations:
  branch: master
This transformation results in a Service resource similar to: 
apiVersion: v1
kind: Service
metadata:
  annotations:
    branch: master
  labels:
    org: KodeKloud
    name: api-service
    namespace: auth
spec:
  ports:
  - port: 80
    protocol: TCP
    targetPort: 3000
  selector:
    component: api
    org: KodeKloud
  type: LoadBalancer

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Summary

The common transformations available in Kustomize include:
Transformation TypePurpose
Common Label TransformationAdds specified labels (e.g., org: KodeKloud) to all resources
Namespace TransformationAssigns a specific namespace to all resources
Name Prefix and SuffixAdds predetermined prefixes and suffixes to resource names
Common Annotation TransformationAppends specific annotations (e.g., branch: master) to resources
These methods provide a scalable and systematic approach to maintaining consistent configurations across your Kubernetes resources.
The image lists common transformations for Kubernetes resources, including adding labels, prefixes/suffixes, namespaces, and annotations.
In summary, Kustomize transformers offer a robust and error-resistant way to apply common configurations—such as labels, namespaces, name modifications, and annotations—to your Kubernetes resources, ensuring that your deployments remain consistent and manageable across various environments.

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