> ## 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 list

> This article explains how to use Kustomize to modify lists in Kubernetes resources using JSON 6902 and Strategic Merge Patches.

When customizing Kubernetes resources, you often need to modify lists—such as the `containers` array in a Deployment. Kustomize supports two patch strategies:

* **JSON 6902 patches**: precise, index-based operations (`add`, `replace`, `remove`).
* **Strategic Merge Patches (SMP)**: declarative, merge-key based edits.

Below is a quick comparison:

| Operation    | JSON 6902 Patch                     | Strategic Merge Patch                  |
| ------------ | ----------------------------------- | -------------------------------------- |
| Replace item | Targets an explicit index           | Matches on `name` merge key            |
| Add item     | Uses `add` with `/-` or an index    | Appends new entries by default         |
| Remove item  | Uses `remove` with a specific index | Uses `$patch: delete` on the merge key |

## Base Deployment Example

```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
```

<Callout icon="lightbulb" color="#1CB2FE">
  Every entry in `spec.template.spec.containers` is a YAML list item, so it begins with `-`.
</Callout>

***

## 1. Replacing a Container

### 1.1 JSON 6902 Patch

Add to your `kustomization.yaml`:

```yaml theme={null}
patches:
  - target:
      kind: Deployment
      name: api-deployment
    patch: |-
      - op: replace
        path: /spec/template/spec/containers/0
        value:
          name: haproxy
          image: haproxy
```

Resulting section:

```yaml theme={null}
spec:
  template:
    spec:
      containers:
        - name: haproxy
          image: haproxy
```

### 1.2 Strategic Merge Patch

Create a file `replace-container.yaml`:

```yaml theme={null}
apiVersion: apps/v1
kind: Deployment
metadata:
  name: api-deployment
spec:
  template:
    spec:
      containers:
        - name: nginx
          image: haproxy
```

Reference it in `kustomization.yaml`:

```yaml theme={null}
patches:
  - replace-container.yaml
```

Kustomize finds the item with `name: nginx` and updates its image.

***

## 2. Adding a Container

### 2.1 JSON 6902 Patch

To append at the end:

```yaml theme={null}
patches:
  - target:
      kind: Deployment
      name: api-deployment
    patch: |-
      - op: add
        path: /spec/template/spec/containers/-
        value:
          name: haproxy
          image: haproxy
```

Result:

```yaml theme={null}
spec:
  template:
    spec:
      containers:
        - name: nginx
          image: nginx
        - name: haproxy
          image: haproxy
```

You can also insert at a specific index by replacing `-` with `1`, `2`, etc.

<Callout icon="triangle-alert" color="#FF6B6B">
  Using `path: /containers/-` always appends. For precise position, specify the index.
</Callout>

### 2.2 Strategic Merge Patch

File `add-container.yaml`:

```yaml theme={null}
apiVersion: apps/v1
kind: Deployment
metadata:
  name: api-deployment
spec:
  template:
    spec:
      containers:
        - name: haproxy
          image: haproxy
```

In your `kustomization.yaml`:

```yaml theme={null}
patches:
  - add-container.yaml
```

The new `haproxy` container is appended automatically.

***

## 3. Removing a Container

Assume this deployment:

```yaml theme={null}
apiVersion: apps/v1
kind: Deployment
metadata:
  name: api-deployment
spec:
  replicas: 1
  template:
    spec:
      containers:
        - name: web
          image: nginx
        - name: database
          image: mongo
```

### 3.1 JSON 6902 Patch

To remove the second container (index 1):

```yaml theme={null}
patches:
  - target:
      kind: Deployment
      name: api-deployment
    patch:
      - op: remove
        path: /spec/template/spec/containers/1
```

After applying, only `web` remains.

### 3.2 Strategic Merge Patch

Create `remove-database.yaml`:

```yaml theme={null}
apiVersion: apps/v1
kind: Deployment
metadata:
  name: api-deployment
spec:
  template:
    spec:
      containers:
        - $patch: delete
          name: database
```

Include it in `kustomization.yaml`:

```yaml theme={null}
patches:
  - remove-database.yaml
```

Kustomize deletes the container with `name: database`.

***

## Links and References

* [Kustomize Documentation](https://kubectl.docs.kubernetes.io/references/kustomize/)
* [JSON Patch (RFC 6902)](https://tools.ietf.org/html/rfc6902)
* [Strategic Merge Patch](https://kubectl.docs.kubernetes.io/guides/strategic-merge-patch/)
* [Kubernetes Pods and Containers](https://kubernetes.io/docs/concepts/workloads/pods/)

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