Components

In this guide, you’ll learn how to define and consume components in Kustomize. Components let you package optional features—such as additional resources, patches, ConfigMaps, or Secrets—into self-contained units. You can then import them in selected overlays without duplicating code, ensuring consistency and reducing configuration drift.

When to Use Components

Use components when an application offers optional features that only apply to some overlays. If a feature is required in all overlays, include it in your base. For features needed by only a subset, bundle them as components to avoid repetition.

Visual Example

Consider three deployment environments:

• dev (development)
• premium (for premium customers)
• standalone (self-hosted)

Our shared base/ folder holds common resources. We also have two optional features:

• Caching (backed by Redis) — enabled in premium and standalone
• External DB (Postgres) — enabled in dev and premium

Where should we place the Redis and Postgres manifests so only the right overlays include them?

Instead of duplicating manifests in overlays—or adding unwanted features to base—we create two components (caching and db) and import them selectively.

Component Features Table

Project Structure

k8s/
├── base/
│   ├── api-depl.yaml
│   └── kustomization.yaml
├── components/
│   ├── caching/
│   │   ├── kustomization.yaml
│   │   ├── deployment-patch.yaml
│   │   └── redis-depl.yaml
│   └── db/
│       ├── kustomization.yaml
│       ├── deployment-patch.yaml
│       └── postgres-depl.yaml
└── overlays/
    ├── dev/
    │   └── kustomization.yaml
    ├── premium/
    │   └── kustomization.yaml
    └── standalone/
        └── kustomization.yaml

• base/: Common resources (e.g., API Deployment)
• components/: Feature directories (caching/, db/)
• overlays/: Environment-specific kustomizations

Database Component

The db component adds a Postgres deployment, a Secret for credentials, and patches your API Deployment.

postgres-depl.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: postgres-deployment
spec:
  replicas: 1
  selector:
    matchLabels:
      component: postgres
  template:
    metadata:
      labels:
        component: postgres
    spec:
      containers:
        - name: postgres
          image: postgres:latest

kustomization.yaml (Component)

apiVersion: kustomize.config.k8s.io/v1alpha1
kind: Component
resources:
  - postgres-depl.yaml
secretGenerator:
  - name: postgres-cred
    literals:
      - password=postgres123
patches:
  - deployment-patch.yaml

deployment-patch.yaml

This strategic merge patch injects the DB_PASSWORD from the Secret into your API Deployment:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: api-deployment
spec:
  template:
    spec:
      containers:
        - name: api
          env:
            - name: DB_PASSWORD
              valueFrom:
                secretKeyRef:
                  name: postgres-cred
                  key: password

Overlay Configuration

Each overlay’s kustomization.yaml pulls in base plus the desired components.

Example: Dev Overlay

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

• premium overlay adds both ../../components/db and ../../components/caching.
• standalone overlay adds only ../../components/caching.

With Kustomize components, you can define optional feature logic once and enable it in any overlay by adding a single entry.

Links and References

• Kustomize Documentation
• Kubernetes Concepts: Overlays
• Redis Official Image
• Postgres Official Image