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How to Configure Kubernetes Resources with Kustomize

Author: Mayank Debnath

Last Updated: Fri, Sep 16, 2022
Kubernetes

Introduction

Kustomize is a configuration management tool. It simplifies the declaration of Kubernetes manifest files by providing features such as patches, generators, transformers, and validators. It introduces an alternative to manifest template management solutions like Helm. Version 1.14 onwards Kustomize comes built into the kubectl command line tool as apply -k. It helps transverse a Kubernetes manifest to add, remove or update configuration options.

Kustomize enables you to make selective patches to a base manifest file to create new variants such as staging, development, production, and so on with different configuration options. It follows the same declarative approach as Kubernetes itself. The native integration with the kubectl command-line tool makes it easier for you to implement Kustomize on your Vultr Kubernetes Engine (VKE) cluster to build and manage application configurations.

This article walks you through the configuration of standard settings like namespace or name prefixes, the configuration of base and overlays to set up different variants, and the configuration of overlay patches. It also explains the installation of the kustomize individual binary that allows previewing plain manifests generated using Kustomize.

Prerequisites

On the management workstation:

You must perform the rest of the steps in this guide from your management workstation.

Set Up the Environment

Kustomize comes built into the kubectl command line tool, but the integration between the two does not allow previewing the configuration. The individual kustomize binary allows building the configuration without applying it to the cluster, and you can use it to generate a plain Kubernetes manifest to preview the generated configuration.

Download the Kustomize installation script.

# wget https://raw.githubusercontent.com/kubernetes-sigs/kustomize/master/hack/install_kustomize.sh

The above command downloads the installation script, which determines the operating system and the system architecture of the management workstation to download the latest pre-complied kustomize binary file.

Run the Kustomize installation script.

# bash install_kustomize.sh

The above command downloads the kustomize binary file into the working directory.

Move the kustomize binary file to the /usr/local/bin directory.

# mv kustomize /usr/local/bin

The above command moves the kustomize binary file to the /usr/local/bin directory to be available globally.

Create and enter a new directory.

# mkdir /kustomize-demo
# cd /kustomize-demo

The above command creates and enters a directory named kustomize-demo in the /root directory.

Using a text editor, create a new manifest file named deployment.yaml.

# nano deployment.yaml

Add the following contents to the file and save the file using CTRL X then ENTER.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx
spec:
  replicas: 1
  selector:
    matchLabels:
      app: nginx-kustomize
  template:
    metadata:
      labels:
        app: nginx-kustomize
    spec:
      containers:
      - image: nginx
        name: nginx

The above manifest file defines a basic Deployment resource using the nginx image.

Create a new manifest file named service.yaml.

# nano service.yaml

Add the following contents to the file and save the file using CTRL X then ENTER.

apiVersion: v1
kind: Service
metadata:
  name: nginx-svc
spec:
  selector:
    app: nginx-kustomize
  ports:
    - protocol: TCP
      port: 80
      targetPort: 80

The above manifest file defines a basic Service resource which by default creates a ClusterIP service resource to expose the connection to pods matching with the defined selector to the cluster.

Create a new manifest file named kustomization.yaml.

# nano kustomization.yaml

Add the following contents to the file and save the file using CTRL X then ENTER.

resources:
- deployment.yaml
- service.yaml

The above manifest enables using the features of Kustomize, as demonstrated in the next sections. The kustomization.yaml file is manifest that specifies a list of resources, patches to apply, configMap and secret generators, and so on. You specify the manifest files under the resources attribute, which merge when you build the configuration.

Build and preview the configuration.

# kustomize build .

The above command outputs the merged configuration of the manifest files listed under the resources attribute.

Apply the configuration.

# kubectl apply -k .

The above command uses the -k flag, which uses the kustomization.yaml file in the given directory to generate a plain manifest and apply changes to the cluster.

Verify the deployment.

# kubectl get all

Output.

NAME                         READY   STATUS    RESTARTS   AGE
pod/nginx-74cd6f44f6-l9brg   1/1     Running   0          30s

NAME                 TYPE        CLUSTER-IP     EXTERNAL-IP   PORT(S)   AGE
service/kubernetes   ClusterIP   10.245.0.1     <none>        443/TCP   10d
service/nginx-svc    ClusterIP   10.245.232.0   <none>        80/TCP    30s

NAME                    READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/nginx   1/1     1            1           30s

NAME                               DESIRED   CURRENT   READY   AGE
replicaset.apps/nginx-74cd6f44f6   1         1         1       30

Delete the deployment.

# kubectl delete -k .

The above command deletes the resources from the cluster.

Configure Common Settings

You can configure common settings such as labels, annotations, namespace, name prefixes, or name suffixes using Kustomize across all the manifest files included in the kustomization.yaml file. Configuring common settings using Kustomize reduces the repetitive code among all the other manifest files while making it easier for the operator to keep the settings in sync in case of any changes reducing the risk of human error.

Create a new manifest file named namespace.yaml.

# nano namespace.yaml

Add the following contents to the file and save the file using CTRL X then ENTER.

apiVersion: v1
kind: Namespace
metadata:
  name: test

The above manifest file declares a new namespace resource named test. You include this manifest file under the resources attribute in the kustomization.yaml file. Kubectl tries to create other resources before creating the namespace resource, which makes creating a new manifest file to define the namespace necessary.

Edit the kustomization.yaml manifest file.

# nano kustomization.yaml

Add the following contents to the file and save the file using CTRL X then ENTER.

resources:
- deployment.yaml
- service.yaml
- namespace.yaml

namespace: test
namePrefix: test-

commonLabels:
  owner: mayank

The above manifest file uses the namespace and the namePrefix attribute, which sets the common namespace and name prefix of the resources defined in the included manifest files. Also, it uses the commonLabels attribute that accepts a list of key-value pairs which set common labels across all the resources. You can also use nameSuffix and commonAnnotations setting up name suffixes and common annotations.

Build and preview the configuration.

# kustomize build .

The above command generates a plain manifest containing all the resources in the Kustomize manifest file modified according to the common settings.

Apply the configuration.

# kubectl apply -k .

Verify the deployment.

# kubectl get all -n test

Output.

NAME                              READY   STATUS    RESTARTS   AGE
pod/test-nginx-5ff865b54d-lw5vk   1/1     Running   0          18s

NAME                     TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)   AGE
service/test-nginx-svc   ClusterIP   10.245.205.173   <none>        80/TCP    19s

NAME                         READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/test-nginx   1/1     1            1           19s

NAME                                    DESIRED   CURRENT   READY   AGE
replicaset.apps/test-nginx-5ff865b54d   1         1         1       19s

Delete the deployment.

# kubectl delete -k .

Configure Base and Overlays

You can configure different variants of your existing manifest files to adapt to environments such as staging, development, production, and so on using Kustomize utilizing base and overlays. This section explains the configuration of base and overlays and setting common settings like name prefixes and labels across all the resources included in the kustomization.yaml file.

The following is a metadata directory structure inside the project directory for configuring multiple variants based on the main manifest files.

base/
- deployment.yaml
- service.yaml
- kustomization.yaml
overlays/
  development/
  - kustomization.yaml
  production/
  - kustomization.yaml

Edit the kustomization.yaml file.

# nano kustomization.yaml

Overwrite the file with the following content and save it using CTRL X then ENTER.

resources:
- deployment.yaml
- service.yaml

Delete the namespace.yaml file.

# rm -f namespace.yaml

Create a new directory named base.

# mkdir base

Move the manifest files to the base directory.

# mv *.yaml base/

The previous section demonstrated the configuration of a common namespace among all the included resources. This section does not include the steps to configure a common namespace for each variant as it adds many repetitive steps, such as creating a namespace.yaml file and so on. The steps to configure the common namespace when using base and overlays remain unchanged where you create a namespace.yaml file to declare a new Namespace resource and mention that file under the resources attribute in the Kustomize manifest file.

Create a new directory named overlays.

# mkdir overlays

Create development and production sub-directories inside the overlays folder.

# mkdir overlays/development overlays/production

Create the Kustomize manifest file for the development variant.

# nano overlays/development/kustomization.yaml

Add the following contents to the file and save the file using CTRL X then ENTER.

bases:
- ../../base

namePrefix: dev-

Create the Kustomize manifest file for the production variant.

# nano overlays/production/kustomization.yaml

Add the following contents to the file and save the file using CTRL X then ENTER.

bases:
- ../../base

namePrefix: prod-

Build and preview the configurations.

# kustomize build overlays/development
# kustomize build overlays/production

Apply the configurations.

# kubectl apply -k overlays/development
# kubectl apply -k overlays/production

The above commands generate and apply a plain manifest using Kustomize for each variant containing all the resources in the base variant with a name prefix according to the value set to the namePrefix attribute in the kustomization.yaml.

Verify the deployment.

# kubectl get all

Output.

NAME                              READY   STATUS    RESTARTS   AGE
pod/dev-nginx-74cd6f44f6-fmg7r    1/1     Running   0          8s
pod/prod-nginx-74cd6f44f6-szf2p   1/1     Running   0          17s

NAME                     TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)   AGE
service/dev-nginx-svc    ClusterIP   10.245.28.102   <none>        80/TCP    8s
service/kubernetes       ClusterIP   10.245.0.1      <none>        443/TCP   9d
service/prod-nginx-svc   ClusterIP   10.245.246.9    <none>        80/TCP    17s

NAME                         READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/dev-nginx    1/1     1            1           8s
deployment.apps/prod-nginx   1/1     1            1           17s

NAME                                    DESIRED   CURRENT   READY   AGE
replicaset.apps/dev-nginx-74cd6f44f6    1         1         1       9s
replicaset.apps/prod-nginx-74cd6f44f6   1         1         1       18s

Delete the deployment.

# kubectl delete -k overlays/development
# kubectl delete -k overlays/production

Configure Overlay Patches

You can patch the existing manifest files using Kustomize to configure advanced settings like memory usage, image name or tag, service type, and so on. This section explains the configuration of overlay patches for configuring the different amounts of replicas, image name or tag, and service type for the resources included in the kustomization.yaml file.

Update Replica Count

The replicas attribute allows changing the number of replicas spawned for any resource included in the Kustomize manifest file. It accepts the name matching the resource and the updated replica count. Here, you update the replica count for the Deployment resource named nginx in the production overlay from 1 to 3.

Edit the Kustomize manifest file.

# nano overlays/production/kustomization.yaml

Make the following changes to the file and save the file using CTRL X then ENTER.

bases:
- ../../base

namePrefix: prod-

replicas:
- name: nginx
  count: 3

Build and preview the configurations.

# kustomize build overlays/production

Apply the configurations.

# kubectl apply -k overlays/production

Verify the deployment.

# kubectl get deployment

Output.

NAME         READY   UP-TO-DATE   AVAILABLE   AGE
prod-nginx   3/3     3            3           7s

Delete the deployment.

# kubectl delete -k overlays/production

Update Image Parameters

The images attribute allows changing the image name or the image tag of any resource included in the Kustomize manifest file. It accepts the name used for matching the resource and values for a new name or new tag using the newName and the newTag attributes. Here, you update the image name for the Deployment resource named nginx in the production overlay from nginx to httpd.

Edit the Kustomize manifest file.

# nano overlays/production/kustomization.yaml

Make the following changes to the file and save the file using CTRL X then ENTER.

bases:
- ../../base

namePrefix: prod-

replicas:
- name: nginx
  count: 3

images:
- name: nginx
  newName: httpd

Apply the configurations.

# kubectl apply -k overlays/production

Verify the deployment.

# kubectl get deployment -o wide

Output.

NAME         READY   UP-TO-DATE   AVAILABLE   AGE    CONTAINERS   IMAGES   SELECTOR
prod-nginx   3/3     3            3           2m5s   nginx        httpd    app=nginx-kustomize

The output confirms the updated image name. You can also change the image tag of any resource included in the Kustomize manifest file. Refer to the images documentation for more information.

Delete the deployment.

# kubectl delete -k overlays/production

Update Resource Specification

The patches attribute allows changing any specification like memory allocation, service type, storage class, and any resource included in the Kustomize manifest file. It accepts a list of manifest file names. Kustomize uses the contents of the included files for matching the resource using the metadata.name attribute. Here, you update the service type of the Service resource named nginx-svc in the production overlay from ClusterIP to NodePort.

Create a new manifest file named service-patch.yaml.

# nano overlays/production/service-patch.yaml

Add the following contents to the file and save the file using CTRL X then ENTER.

apiVersion: v1
kind: Service
metadata:
  name: nginx-svc
spec:
  type: NodePort

Edit the Kustomize manifest file.

# nano overlays/production/kustomization.yaml

Make the following changes to the file and save the file using CTRL X then ENTER.

bases:
- ../../base

namePrefix: prod-

replicas:
- name: nginx
  count: 3

images:
- name: nginx
  newName: httpd

patches:
- service-patch.yaml

Apply the configurations.

# kubectl apply -k overlays/production

Verify the deployment.

# kubectl get svc

Output.

NAME             TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)        AGE
kubernetes       ClusterIP   10.245.0.1       <none>        443/TCP        10d
prod-nginx-svc   NodePort    10.245.251.102   <none>        80:31842/TCP   6m42s

The output confirms the updated service type. The patches attribute is not limited to updating the type. It allows you to change any resource specification included in the Kustomize manifest file by creating a manifest file to patch the resource, as demonstrated above.

Delete the deployment.

# kubectl delete -k overlays/production

Conclusion

You learned the basic usage of the Kustomize configuration management tool, including the configuration of common settings like namespace or name prefixes, the configuration of base and overlays to set up different variants, and the configuration of overlay patches. You also installed the kustomize individual binary to preview configurations before applying them using kubectl. These operations are a good starting point for integrating Kustomize into your workflow, and you can refer to the Kustomize documentation for more information.

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