> ## Documentation Index
> Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Patches Intro

> Kustomize patches allow precise updates to individual Kubernetes resources without affecting all objects in an overlay.

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.

## 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`)

<Frame>
  ![The image is a slide explaining how Kustomize patches modify Kubernetes configurations, highlighting the need for three parameters: operation type, target resource, and value.](https://kodekloud.com/kk-media/image/upload/v1752880926/notes-assets/images/Kustomize-Patches-Intro/kustomize-patches-kubernetes-configurations-slide.jpg)
</Frame>

| Operation | Description                 | Example                           |
| --------- | --------------------------- | --------------------------------- |
| add       | Append a field or container | Add a sidecar container to a Pod  |
| remove    | Delete a field or label     | Remove an unwanted annotation     |
| replace   | Update an existing value    | Change replica count from 5 to 10 |

<Callout icon="lightbulb" color="#1CB2FE">
  Use patches for fine-grained updates that shouldn’t apply globally. For bulk changes—like adding a common label—stick to transformers.
</Callout>

### Defining the Target

Specify one or more match criteria under `target` to pinpoint resources:

```yaml theme={null}
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.

***

## JSON 6902 Patch Example

Below is a basic `Deployment` manifest:

```yaml theme={null}
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:

```yaml theme={null}
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`:

```yaml theme={null}
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
```

<Callout icon="lightbulb" color="#1CB2FE">
  JSON 6902 patches consist of an array of operations (`op`, `path`, `value`). Refer to the [RFC 6902](https://tools.ietf.org/html/rfc6902) for full details.
</Callout>

### Updating Replicas

To adjust the replica count, update the `path` to `/spec/replicas` and set the desired value:

```yaml theme={null}
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.

***

## Strategic Merge Patch

Strategic merge patches let you describe only the fields to modify, using standard Kubernetes YAML:

```yaml theme={null}
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.

<Callout icon="triangle-alert" color="#FF6B6B">
  You can combine JSON 6902 and strategic merge patches in the same `kustomization.yaml`. Use whichever format fits your use case.
</Callout>

***

## Links and References

* [Kustomize Documentation](https://kubectl.docs.kubernetes.io/references/kustomize/)
* [RFC 6902: JSON Patch](https://tools.ietf.org/html/rfc6902)
* [Kubernetes API Conventions](https://github.com/kubernetes/community/blob/master/contributors/devel/sig-architecture/api-conventions.md)

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