# Customization of kubernetes YAML configurations


# kustomize

`kustomize` lets you customize raw, template-free YAML files for multiple purposes, leaving the original YAML untouched and usable as is.

`kustomize` targets kubernetes; it understands and can patch [kubernetes style](https://kubectl.docs.kubernetes.io/references/kustomize/glossary/#kubernetes-style-object) API objects. It's like [`make`](https://www.gnu.org/software/make), in that what it does is declared in a file, and it's like [`sed`](https://www.gnu.org/software/sed), in that it emits edited text.

## kubectl integration

To find the kustomize version embedded in recent versions of kubectl, run `kubectl version`:

```basic
> kubectl version --client
Client Version: v1.31.0
Kustomize Version: v5.4.2
```

The kustomize build flow at [v2.0.3](https://github.com/kubernetes-sigs/kustomize/releases/tag/v2.0.3) was added to [kubectl v1.14](https://kubernetes.io/blog/2019/03/25/kubernetes-1-14-release-announcement). The kustomize flow in kubectl remained frozen at v2.0.3 until kubectl v1.21, which [updated it to v4.0.5](https://github.com/kubernetes/kubernetes/blob/4d75a6238a6e330337526e0513e67d02b1940b63/CHANGELOG/CHANGELOG-1.21.md#kustomize-updates-in-kubectl). It will be updated on a regular basis going forward, and such updates will be reflected in the Kubernetes release notes.

| Kubectl version | Kustomize version |
| --- | --- |
| < v1.14 | n/a |
| v1.14-v1.20 | v2.0.3 |
| v1.21 | v4.0.5 |
| v1.22 | v4.2.0 |
| v1.23 | v4.4.1 |
| v1.24 | v4.5.4 |
| v1.25 | v4.5.7 |
| v1.26 | v4.5.7 |
| v1.27 | v5.0.1 |

For examples and guides for using the kubectl integration please see the [kubernetes documentation](https://kubernetes.io/docs/tasks/manage-kubernetes-objects/kustomization/).

## Usage

### 1) Make a [kustomization](https://kubectl.docs.kubernetes.io/references/kustomize/glossary/#kustomization) file

In some directory containing your YAML [resource](https://kubectl.docs.kubernetes.io/references/kustomize/glossary/#resource) files (deployments, services, configmaps, etc.), create a [kustomization](https://kubectl.docs.kubernetes.io/references/kustomize/glossary/#kustomization) file.

This file should declare those resources, and any customization to apply to them, e.g. *add a common label*.

```basic

base: kustomization + resources

kustomization.yaml                                      deployment.yaml                                                 service.yaml
+---------------------------------------------+         +-------------------------------------------------------+       +-----------------------------------+
| apiVersion: kustomize.config.k8s.io/v1beta1 |         | apiVersion: apps/v1                                   |       | apiVersion: v1                    |
| kind: Kustomization                         |         | kind: Deployment                                      |       | kind: Service                     |
| commonLabels:                               |         | metadata:                                             |       | metadata:                         |
|   app: myapp                                |         |   name: myapp                                         |       |   name: myapp                     |
| resources:                                  |         | spec:                                                 |       | spec:                             |
|   - deployment.yaml                         |         |   selector:                                           |       |   selector:                       |
|   - service.yaml                            |         |     matchLabels:                                      |       |     app: myapp                    |
| configMapGenerator:                         |         |       app: myapp                                      |       |   ports:                          |
|   - name: myapp-map                         |         |   template:                                           |       |     - port: 6060                  |
|     literals:                               |         |     metadata:                                         |       |       targetPort: 6060            |
|       - KEY=value                           |         |       labels:                                         |       +-----------------------------------+
+---------------------------------------------+         |         app: myapp                                    |
                                                        |     spec:                                             |
                                                        |       containers:                                     |
                                                        |         - name: myapp                                 |
                                                        |           image: myapp                                |
                                                        |           resources:                                  |
                                                        |             limits:                                   |
                                                        |               memory: "128Mi"                         |
                                                        |               cpu: "500m"                             |
                                                        |           ports:                                      |
                                                        |             - containerPort: 6060                     |
                                                        +-------------------------------------------------------+

```

File structure:

> ```basic
> ~/someApp
> ├── deployment.yaml
> ├── kustomization.yaml
> └── service.yaml
> ```

The resources in this directory could be a fork of someone else's configuration. If so, you can easily rebase from the source material to capture improvements, because you don't modify the resources directly.

Generate customized YAML with:

```basic
kustomize build ~/someApp
```

The YAML can be directly [applied](https://kubectl.docs.kubernetes.io/references/kustomize/glossary/#apply) to a cluster:

> ```basic
> kustomize build ~/someApp | kubectl apply -f -
> ```

### 2) Create [variants](https://kubectl.docs.kubernetes.io/references/kustomize/glossary/#variant) using [overlays](https://kubectl.docs.kubernetes.io/references/kustomize/glossary/#overlay)

Manage traditional [variants](https://kubectl.docs.kubernetes.io/references/kustomize/glossary/#variant) of a configuration - like *development*, *staging* and *production* - using [overlays](https://kubectl.docs.kubernetes.io/references/kustomize/glossary/#overlay) that modify a common [base](https://kubectl.docs.kubernetes.io/references/kustomize/glossary/#base).

```basic

overlay: kustomization + patches

kustomization.yaml                                      replica_count.yaml                      cpu_count.yaml
+-----------------------------------------------+       +-------------------------------+       +------------------------------------------+
| apiVersion: kustomize.config.k8s.io/v1beta1   |       | apiVersion: apps/v1           |       | apiVersion: apps/v1                      |
| kind: Kustomization                           |       | kind: Deployment              |       | kind: Deployment                         |
| commonLabels:                                 |       | metadata:                     |       | metadata:                                |  
|   variant: prod                               |       |   name: myapp                 |       |   name: myapp                            |
| resources:                                    |       | spec:                         |       | spec:                                    |
|   - ../../base                                |       |   replicas: 80                |       |  template:                               |
| patches:                                      |       +-------------------------------+       |     spec:                                |
|   - path: replica_count.yaml                  |                                               |       containers:                        |
|   - path: cpu_count.yaml                      |                                               |         - name: myapp                    |  
+-----------------------------------------------+                                               |           resources:                     |
                                                                                                |             limits:                      |
                                                                                                |               memory: "128Mi"            |
                                                                                                |               cpu: "7000m"               |
                                                                                                +------------------------------------------+
```

File structure:

> ```basic
> ~/someApp
> ├── base
> │   ├── deployment.yaml
> │   ├── kustomization.yaml
> │   └── service.yaml
> └── overlays
>     ├── development
>     │   ├── cpu_count.yaml
>     │   ├── kustomization.yaml
>     │   └── replica_count.yaml
>     └── production
>         ├── cpu_count.yaml
>         ├── kustomization.yaml
>         └── replica_count.yaml
> ```

Take the work from step (1) above, move it into a `someApp` subdirectory called `base`, then place overlays in a sibling directory.

An overlay is just another kustomization, referring to the base, and referring to patches to apply to that base.

This arrangement makes it easy to manage your configuration with `git`. The base could have files from an upstream repository managed by someone else. The overlays could be in a repository you own. Arranging the repo clones as siblings on disk avoids the need for git submodules (though that works fine, if you are a submodule fan).

Generate YAML with

```basic
kustomize build ~/someApp/overlays/production
```

The YAML can be directly [applied](https://kubectl.docs.kubernetes.io/references/kustomize/glossary/#apply) to a cluster:

> ```basic
> kustomize build ~/someApp/overlays/production | kubectl apply -f -
> ```

## Community

* [file a bug](https://kubectl.docs.kubernetes.io/contributing/kustomize/bugs/)
    
* [contribute a feature](https://kubectl.docs.kubernetes.io/contributing/kustomize/features/)
    
* [propose a larger enhancement](https://github.com/kubernetes-sigs/kustomize/tree/master/proposals)
    

### Code of conduct

Participation in the Kubernetes community is governed by the [Kubernetes Code of Conduct](https://github.com/kubernetes-sigs/kustomize/blob/master/code-of-conduct.md).