kustomize

An Introduction to Kustomize

Kustomize is a powerful tool for managing Kubernetes configurations. It allows users to customize raw YAML files for various purposes without altering the original files. This feature makes it uniquely advantageous for developers and administrators working with Kubernetes, as it provides flexibility and ensures that the original configurations remain intact for future use.

Target and Functionality

Specifically designed for Kubernetes, Kustomize has the ability to understand and adjust API objects in a Kubernetes style. This makes it akin to tools like make and sed—with make, users declare actions in a file, and like sed, it outputs edited text, making Kustomize particularly suited for configuration management and deployment tasks in Kubernetes environments.

Integration with Kubectl

Kustomize is integrated into kubectl, the command-line interface for Kubernetes. Users can check the embedded version of Kustomize within their kubectl by running the command:

> kubectl version --client

The tool has evolved through various versions integrated into kubectl, starting from version 2.0.3 in kubectl v1.14 to version 5.0.1 in kubectl v1.27, with updates regularly included in Kubernetes release notes. This integration means users have direct access to Kustomize functionalities as part of their Kubernetes management toolkit.

Basic Usage

Creating a Kustomization File

A typical use of Kustomize begins with the creation of a kustomization.yaml file in the directory where the YAML resource files (like deployments and services) reside. This file declares the resources and desired customizations—such as adding common labels or configuration maps.

Example structure:

~/someApp
├── deployment.yaml
├── kustomization.yaml
└── service.yaml

Running the following command generates the customized YAML:

kustomize build ~/someApp

The resulting YAML can be applied directly to a Kubernetes cluster:

kustomize build ~/someApp | kubectl apply -f -

Creating Variants with Overlays

For managing different configurations (e.g., development, staging, production), Kustomize uses the concept of overlays—modifications built on a common base configuration. These overlays are separate kustomization.yaml files that implement additional patches on top of the base configuration.

Example project structure with overlays:

~/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

To generate YAML for a specific variant, such as production, run:

kustomize build ~/someApp/overlays/production

And apply it directly to the cluster:

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

Community and Contribution

Kustomize is an open project with opportunities for community interaction. Users can file bugs, contribute features, or suggest enhancements through its GitHub repository. They also operate under the [Kubernetes Code of Conduct], ensuring a respectful and collaborative community environment.

In summary, Kustomize offers a robust and flexible approach to managing Kubernetes configurations, making it easier to handle different environments without compromising the integrity of the original files. It's indispensable for anyone looking to harness the full potential of Kubernetes deployment strategies.