Kustomize — Kubernetes Config. Management

Kubernetes

Published

April 16, 2025

Modified

April 23, 2025

Kustomize¹ — Customizing Kubernetes application configurations

kubectl native …no separate dependency
Plain YAML …does not use template/DSL (like Helm)
…compose/customize collections of resources
…generate resources from other sources (for example simple files)
…patches to introduce environment specific changes

Terminology:

Generator — Makes a resource
Patch — General instructions to modify a resource
Overlay — Kustomization that depends on another kustomization
Base — Kustomization referred to by some other kustomization

`kustomization.yaml`

Term “kustomization” refers to akustomization.yaml file…

…aka a directory containing this file
…describes how to generate or transform resources
Containers fields in the following categories:
- resources …what existing resources are to be customized.
- generators …what new resources should be created
- transformers …what to do to the aforementioned resources
- meta …fields which may influence all or some of the above

Examples:

# create a simple resource
cat > volume.yaml <<EOF
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: volume
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi
  storageClassName: rook-ceph-block
EOF

# create a kustomization
cat > kustomization.yaml <<EOF
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
namePrefix: example-prefix-
resources:
- volume.yaml
EOF

$target must be a path or a URL to a kustomization (can be a base/overlay)

kubectl kustomize $target

# …send it to the apply operation
kubectl kustomize $target | kubectl apply -f -

Kustomization

Reference the docuemntation for Kustomize’s built-in transformers and generators² and the content of kustomization.yaml³

Names

Resource names…

namePrefix: example-prefix-            # add prefix to names
nameSuffix: -suffix                    # add suffix to names
namespace: example-namespace           # add a namespace
labels:                                # add labels
- pairs:
    service: example
    environment: development

Create and use a namespace…

kustomization.yaml

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
namespace: example
resources:
- ./namespace.yml
#…

namespace.yaml

apiVersion: v1
kind: Namespace
metadata:
  name: example

Resources

Each entry in this list must be a path to a file (or URL):

…files container Kubernetes API resources
…paths should be specified relative to the kustomization file
…processed in depth-first order

resources:
# Local files
- volume.yaml
- deployment.yaml
- path/to/secret.yaml
# Local directories
- ../../path/
# Remote URLs
- https://....

ConfigMaps

Generate ConfigMap resources⁴:

Generation sources…
- literals — Key/value as data specified in kustomization.yaml
- env. file — File with key-value pairs relative to kustomization.yaml
- file — Complete configuration file relative to kustomization.yaml
Name of the generated resource automatically identified & referenced
Changes to content (will change the name suffix) …recreates of the ConfigMap

Generate a ConfigMap with a data item containing the contents of a file

kustomization.yaml

# create a ConfigMap from a file (relative path)
configMapGenerator:
- name: nginx-conf
  files:
    - etc/nginx.conf

pod.yaml

#...
spec:
  volumes:
  - name: nginx-conf
    configMap:
      name: nginx-conf
      items:
      - key: nginx.conf
        path: nginx.conf
#...
  containers:
  - name: httpd-server
    image: nginx:alpine
    # mount the configuration into a container
    volumeMounts:
    - name: nginx-conf
      mountPath: /etc/nginx/nginx.conf
      subPath: nginx.conf
      readOnly: true
#...

Footnotes

Kustomize Project
https://kustomize.io
https://github.com/kubernetes-sigs/kustomize ↩︎
Kustomize Reference Documentation
https://kubectl.docs.kubernetes.io/references/kustomize ↩︎
Content of a kustomization file
https://kubectl.docs.kubernetes.io/references/kustomize/kustomization ↩︎
configMapGenerator, Kuberntes Documentation
https://kubectl.docs.kubernetes.io/references/kustomize/kustomization/configmapgenerator/↩︎

--- title: 'Kustomize — Kubernetes Config. Management' categories: - Kubernetes date: 2025/04/16 date-modified: 2025/04/23 toc-expand: 3 --- Kustomize[^pmji7] — Customizing Kubernetes application configurations [^pmji7]: Kustomize Project <https://kustomize.io> <https://github.com/kubernetes-sigs/kustomize> - `kubectl` native …no separate dependency - Plain YAML …does not use template/DSL (like Helm) - …compose/customize collections of resources - …generate resources from other sources (for example simple files) - …patches to introduce environment specific changes Terminology: * **Generator** — Makes a resource * **Patch** — General instructions to modify a resource * **Overlay** — Kustomization that depends on another kustomization * **Base** — Kustomization referred to by some other kustomization ### `kustomization.yaml` Term "kustomization" refers to a`kustomization.yaml` file… * …aka a directory containing this file * …describes how to generate or transform resources * Containers fields in the following categories: - _resources_ …what existing resources are to be customized. - _generators_ …what new resources should be created - _transformers_ …what to do to the aforementioned resources - _meta_ …fields which may influence all or some of the above Examples: ```bash # create a simple resource cat > volume.yaml <<EOF apiVersion: v1 kind: PersistentVolumeClaim metadata: name: volume spec: accessModes: - ReadWriteOnce resources: requests: storage: 1Gi storageClassName: rook-ceph-block EOF # create a kustomization cat > kustomization.yaml <<EOF apiVersion: kustomize.config.k8s.io/v1beta1 kind: Kustomization namePrefix: example-prefix- resources: - volume.yaml EOF ``` `$target` must be a path or a URL to a kustomization (can be a base/overlay) ```bash kubectl kustomize $target # …send it to the apply operation kubectl kustomize $target | kubectl apply -f - ``` ## Kustomization Reference the docuemntation for Kustomize’s built-in transformers and generators[^19jKl] and the **content of `kustomization.yaml`**[^6gHJk] [^19jKl]: Kustomize Reference Documentation <https://kubectl.docs.kubernetes.io/references/kustomize> [^6gHJk]: Content of a kustomization file <https://kubectl.docs.kubernetes.io/references/kustomize/kustomization> ### Names Resource names… ```yaml namePrefix: example-prefix- # add prefix to names nameSuffix: -suffix # add suffix to names namespace: example-namespace # add a namespace labels: # add labels - pairs: service: example environment: development ``` Create and use a **namespace**… ```{.yaml filename=kustomization.yaml} apiVersion: kustomize.config.k8s.io/v1beta1 kind: Kustomization namespace: example resources: - ./namespace.yml #… ``` ```{.yaml filename=namespace.yaml} apiVersion: v1 kind: Namespace metadata: name: example ``` ### Resources Each entry in this list must be a path to a file (or URL): - …files container Kubernetes API resources - …paths should be specified relative to the kustomization file - …processed in depth-first order ```yaml resources: # Local files - volume.yaml - deployment.yaml - path/to/secret.yaml # Local directories - ../../path/ # Remote URLs - https://.... ``` ### ConfigMaps Generate ConfigMap resources[^f0eZk]: [^f0eZk]: `configMapGenerator`, Kuberntes Documentation <https://kubectl.docs.kubernetes.io/references/kustomize/kustomization/configmapgenerator/> - Generation sources… - **_literals_** — Key/value as data specified in `kustomization.yaml` - **_env. file_** — File with key-value pairs relative to `kustomization.yaml` - **_file_** — Complete configuration file relative to `kustomization.yaml` - _Name_ of the generated resource automatically identified & referenced - Changes to content (will change the name suffix) …recreates of the ConfigMap Generate a ConfigMap with a data item containing the contents of a file ```{.yaml filename=kustomization.yaml} # create a ConfigMap from a file (relative path) configMapGenerator: - name: nginx-conf files: - etc/nginx.conf ``` ```{.yaml filename=pod.yaml} #... spec: volumes: - name: nginx-conf configMap: name: nginx-conf items: - key: nginx.conf path: nginx.conf #... containers: - name: httpd-server image: nginx:alpine # mount the configuration into a container volumeMounts: - name: nginx-conf mountPath: /etc/nginx/nginx.conf subPath: nginx.conf readOnly: true #... ```