Patches Dictionary

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.

Overview

Kustomize supports two main patch mechanisms:

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

1. Replacing a Label

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.

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.

2. Adding a Label

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.

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.

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

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.

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

Links and References

• Kustomize Patches Reference
• JSON Patch (RFC6902)
• Strategic Merge Patch