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Kustomize patches provide a surgical way to update individual Kubernetes resources without affecting all objects in your overlay. While common transformers are ideal for broad changes—such as applying a label or namespace to every resource—patches let you target one or a few objects with precise modifications. For instance, bumping the replica count in a Deployment is best handled via a dedicated patch.

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Key Parameters of a Patch

Every patch in Kustomize requires three core parameters:
  1. Operation type:
    • add → append a new field or item
    • remove → delete an existing field or item
    • replace → swap an existing value for a new one
  2. Target: selection criteria to identify the resource(s) you want to patch
  3. Value: the data to add or replace (not needed for remove)
The image is a slide explaining how Kustomize patches modify Kubernetes configurations, highlighting the need for three parameters: operation type, target resource, and value.
OperationDescriptionExample
addAppend a field or containerAdd a sidecar container to a Pod
removeDelete a field or labelRemove an unwanted annotation
replaceUpdate an existing valueChange replica count from 5 to 10
Use patches for fine-grained updates that shouldn’t apply globally. For bulk changes—like adding a common label—stick to transformers.

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Defining the Target

Specify one or more match criteria under target to pinpoint resources: 
target:
  kind: Deployment
  apiVersion: apps/v1
  name: api-deployment
  namespace: production
  labelSelector: "app=frontend"
Combine kind, apiVersion, name, namespace, labelSelector, or annotationSelector for exact control.

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JSON 6902 Patch Example

Below is a basic Deployment manifest: 
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
Add this inline JSON 6902 patch in your kustomization.yaml to rename the Deployment: 
patches:
  - target:
      kind: Deployment
      name: api-deployment
    patch: |-
      - op: replace
        path: /metadata/name
        value: web-deployment
After running kustomize build, the output changes metadata.name to web-deployment: 
apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-deployment
spec:
  replicas: 1
  selector:
    matchLabels:
      component: api
  template:
    metadata:
      labels:
        component: api
    spec:
      containers:
        - name: nginx
          image: nginx
JSON 6902 patches consist of an array of operations (op, path, value). Refer to the RFC 6902 for full details.

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Updating Replicas

To adjust the replica count, update the path to /spec/replicas and set the desired value: 
patches:
  - target:
      kind: Deployment
      name: api-deployment
    patch: |-
      - op: replace
        path: /spec/replicas
        value: 5
After kustomize build, you’ll see replicas: 5 in the generated manifest.

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Strategic Merge Patch

Strategic merge patches let you describe only the fields to modify, using standard Kubernetes YAML: 
patches:
  - patch: |
      apiVersion: apps/v1
      kind: Deployment
      metadata:
        name: api-deployment
      spec:
        replicas: 5
Here, Kustomize locates the Deployment by apiVersion, kind, and metadata.name, then merges spec.replicas: 5 into the base resource.
You can combine JSON 6902 and strategic merge patches in the same kustomization.yaml. Use whichever format fits your use case.

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