How to use the command 'kustomize' (with examples)

Kustomize is a command-line tool designed to streamline the deployment of Kubernetes resources. It allows users to customize Kubernetes configurations in a straightforward and reusable manner. By organizing Kubernetes resource files, manipulating configurations, and facilitating environment-specific deployments, Kustomize enhances operational efficiency in a DevOps pipeline. This tool is particularly effective in managing multiple environments for Kubernetes, helping to automate resource adjustments and ensure deployments are consistent and controlled.

Use case 1: Create a kustomization file with resources and namespace

Code:

kustomize create --resources deployment.yaml,service.yaml --namespace staging

Motivation:

In a typical Kubernetes setup, managing numerous resources can become complicated. By using a kustomization file, you can keep track of these resources systematically. This use case demonstrates how to create a kustomization file, which is essential for grouping related resources and specifying the namespace they belong in. Specifically, when working in multiple environments like development, testing, and staging, it becomes imperative to scope resources appropriately to avoid conflicts and maintain control of deployments.

Explanation:

• create: This subcommand initializes a new kustomization file in the current directory. It will consist of references to the given resource files.

• --resources deployment.yaml,service.yaml: This argument specifies the resources to include in the kustomization file. Here, two YAML files, deployment.yaml and service.yaml, are referenced, which typically define a Deployment and a Service in Kubernetes, respectively.

• --namespace staging: This flag assigns the resources to the ‘staging’ namespace, facilitating an environment-specific deployment. Namespaces in Kubernetes are virtual clusters within a cluster, used to separate and manage resources.

Example output:

kustomization.yaml created.

Use case 2: Build a kustomization file and deploy it with kubectl

Code:

kustomize build . | kubectl apply -f -

Motivation:

Once you have a kustomization file, the next logical step is to deploy the resources defined within it to your Kubernetes cluster. This example shows how to build the kustomization and immediately deploy it using kubectl, the Kubernetes command-line tool. It’s a seamless way to manage the end-to-end process without manual intervention, especially useful in continuous integration (CI) pipelines.

Explanation:

• build .: The build command processes the kustomization file in the current directory (denoted by .) and prepares it for deployment by generating the fully processed YAML files.

• |: This pipe symbol is used to output the result of the kustomize build command directly as input to the following command (kubectl apply).

• kubectl apply -f -: This tells kubectl to read from the standard input (indicated by the -) and apply the configuration to the Kubernetes cluster, effectively creating or updating the resources.

Example output:

deployment.apps/my-deployment created
service/my-service created

Use case 3: Set an image in the kustomization file

Code:

kustomize edit set image busybox=alpine:3.6

Motivation:

In Kubernetes, images are essential as they define the software that your containers will run. Updating these images frequently is a best practice for applying patches, new features, or versions. Kustomize simplifies this update process across multiple kustomization files without altering the original YAML files for individual resources.

Explanation:

• edit set image: This subcommand modifies the image specified in the kustomization file. It is a way to update image versions centrally for all deployments managed by this file.

• busybox=alpine:3.6: This argument specifies that the image used for ‘busybox’ should be updated to ‘alpine:3.6’. Naming formats are imageName=imageName:imageTag, signifying the target container image and tag.

Example output:

Updated kustomization.yaml to use image busybox with new tag: alpine:3.6

Use case 4: Search for Kubernetes resources in the current directory to be added to the kustomization file

Code:

kustomize create --autodetect

Motivation:

As projects grow, managing which resources are included in deployments can become cumbersome. The autodetect feature allows for automated discovery of these resources in the current directory, making it easier to incorporate all relevant files without having to specify each one manually. It’s highly beneficial when you’re integrating new components or restructuring your Kubernetes application.

Explanation:

• create: As before, initializes a new kustomization file.

• --autodetect: This flag directs Kustomize to automatically discover and include all Kubernetes YAML configuration files present in the current directory. It streamlines the initialization process significantly.

Example output:

kustomization.yaml created, including detected files: deployment.yaml, service.yaml, configmap.yaml

Conclusion:

Kustomize proves to be a robust tool in the Kubernetes ecosystem, offering significant improvements in organization, maintainability, and scalability of Kubernetes deployments. By facilitating resource orchestration through configuration management, Kustomize stands as an essential utility for anyone looking to manage Kubernetes setups efficiently. With these examples, users can gain a fuller understanding of how to leverage this tool effectively for their specific needs.