Transformers Demo

In this tutorial, you’ll learn how to apply common Kustomize transformers—labels, annotations, name prefixes/suffixes, namespaces, and image updates—across your Kubernetes manifests. We’ll use a simple API and database example to demonstrate each feature step by step.

Directory Layout

Our project structure separates API and database manifests into their own folders:

k8s/
├── api/
│   ├── api-depl.yaml
│   ├── api-service.yaml
│   └── kustomization.yaml
└── db/
    ├── db-config.yaml
    ├── db-depl.yaml
    ├── db-service.yaml
    └── kustomization.yaml

Each subdirectory’s kustomization.yaml declares its local resources. For example, api/kustomization.yaml:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
  - api-depl.yaml
  - api-service.yaml

And db/kustomization.yaml:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
  - db-config.yaml
  - db-depl.yaml
  - db-service.yaml

The root kustomization.yaml aggregates both:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
  - api/
  - db/

1. Global Labels with commonLabels

To tag all resources with department=engineering, add a commonLabels section at the root:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
  - api/
  - db/
commonLabels:
  department: engineering

Build the manifests:

kustomize build k8s/

Excerpt of the generated YAML shows the label applied everywhere:

apiVersion: v1
kind: ConfigMap
metadata:
  name: db-credentials
  labels:
    department: engineering
---
apiVersion: v1
kind: Service
metadata:
  name: api-service
  labels:
    department: engineering

2. Scoped Labels in Subdirectories

Labels in a subdirectory only affect its own resources.

API folder example (api/kustomization.yaml):

commonLabels:
  feature: api

After rebuilding:

• API resources include both department=engineering and feature=api.
• DB resources remain only department=engineering.

Similarly, add feature: db to db/kustomization.yaml:

commonLabels:
  feature: db

3. Assigning a Namespace

To place all resources into a namespace (e.g., debugging), set namespace at the root:

namespace: debugging

Rebuild and notice each resource now has:

metadata:
  namespace: debugging

4. Name Prefixes and Suffixes

Global Prefix

In the root kustomization.yaml:

namePrefix: KodeKloud-

Every resource name is prefixed with KodeKloud-.

Subdirectory Suffixes

• api/kustomization.yaml:

  nameSuffix: -web
  

• db/kustomization.yaml:

  nameSuffix: -storage
  

Resulting resource names:

• name: KodeKloud-api-deployment-web
• name: KodeKloud-db-deployment-storage

5. Common Annotations

Add commonAnnotations at the root to include annotations globally:

commonAnnotations:
  logging: verbose

Each manifest’s metadata now contains:

annotations:
  logging: verbose

6. Overriding Container Images

Use the images transformer where needed. In db/kustomization.yaml, override the MongoDB image:

images:
  - name: mongo
    newName: postgres
    newTag: "4.2"

After building, the DB Deployment spec shows:

spec:
  containers:
    - name: mongo
      image: postgres:4.2

Only the specified image is updated; all other container images remain unchanged.

Kustomize Transformers at a Glance

Next, try these transformers hands-on to see how they simplify your Kubernetes deployments.

Links and References

• Kustomize Official Documentation
• Kustomize Transformers Reference
• Kubernetes Concepts: Labels and Selectors