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Learn how to update, add, and remove keys (e.g., labels) in a Kubernetes Deployment using Kustomize. We’ll demonstrate both JSON 6902 patches and Strategic Merge Patches with clear examples and best practices.

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Overview

Kustomize supports two main patch mechanisms:
Patch TypeSyntaxUse CaseReference
JSON 6902 PatchJSON PointerPrecise add, replace, remove opsJSON Patch (RFC6902)
Strategic Merge PatchYAML mergeDeclarative updates, merges by keyStrategic Merge Patch
Use JSON 6902 when you need fine-grained control. Choose Strategic Merge for simpler, declarative label or annotation updates.

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Base Deployment Configuration

Save this as base/api-deployment.yaml: 
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
In the same directory, your kustomization.yaml should include: 
resources:
  - api-deployment.yaml

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1. Replacing a Label

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1.1 JSON 6902 Patch

Add this section under patches in kustomization.yaml: 
patches:
  - target:
      kind: Deployment
      name: api-deployment
    patch: |-
      - op: replace
        path: /spec/template/metadata/labels/component
        value: web
  • op: replace – updates the existing component label.
  • path – JSON Pointer to /spec/template/metadata/labels/component.
  • value: web – new label value.

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1.2 Strategic Merge Patch

Reference an external YAML file in kustomization.yaml: 
patches:
  - label-replace.yaml
Create label-replace.yaml: 
apiVersion: apps/v1
kind: Deployment
metadata:
  name: api-deployment
spec:
  template:
    metadata:
      labels:
        component: web
Kustomize merges only the provided fields, updating component to web.

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2. Adding a Label

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2.1 JSON 6902 Patch

In kustomization.yaml: 
patches:
  - target:
      kind: Deployment
      name: api-deployment
    patch: |-
      - op: add
        path: /spec/template/metadata/labels/org
        value: kodekloud
  • op: add – inserts a new key org.
  • value: kodekloud – label value added under .spec.template.metadata.labels.

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2.2 Strategic Merge Patch

Reference a file in kustomization.yaml: 
patches:
  - label-add.yaml
Create label-add.yaml: 
apiVersion: apps/v1
kind: Deployment
metadata:
  name: api-deployment
spec:
  template:
    metadata:
      labels:
        org: kodekloud
After applying, labels will include both component: api and org: kodekloud.

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3. Removing a Label

Assume the Deployment now has: 
apiVersion: apps/v1
kind: Deployment
metadata:
  name: api-deployment
spec:
  replicas: 1
  selector:
    matchLabels:
      component: api
  template:
    metadata:
      labels:
        component: api
        org: kodekloud
    spec:
      containers:
      - name: nginx
        image: nginx

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3.1 JSON 6902 Patch

In kustomization.yaml: 
patches:
  - target:
      kind: Deployment
      name: api-deployment
    patch: |-
      - op: remove
        path: /spec/template/metadata/labels/org
  • op: remove – deletes the org key.

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3.2 Strategic Merge Patch

Reference in kustomization.yaml: 
patches:
  - label-remove.yaml
Create label-remove.yaml: 
apiVersion: apps/v1
kind: Deployment
metadata:
  name: api-deployment
spec:
  template:
    metadata:
      labels:
        org: null
Setting org: null instructs Kustomize to remove that label key.

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