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Customization of kubernetes YAML configurations
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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 API objects. It's like make, in that what it does is declared in a file, and it's like sed, in that it emits editted text.

This tool is sponsored by sig-cli (KEP), and inspired by DAM.

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Installation: Download a binary from the release page, or see these install notes. Then try one of the tested examples.


1) Make a kustomization file

In some directory containing your YAML resource files (deployments, services, configmaps, etc.), create a kustomization file.

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

base image

File structure:

├── 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:

kustomize build ~/someApp

The YAML can be directly applied to a cluster:

kustomize build ~/someApp | kubectl apply -f -

2) Create variants using overlays

Manage traditional variants of a configuration - like development, staging and production - using overlays that modify a common base.

overlay image

File structure:

├── 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, refering 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

kustomize build ~/someApp/overlays/production

The YAML can be directly applied to a cluster:

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


Filing bug reports

A good report specifies
  • the output of kustomize version,
  • the input (the content of kustomization.yaml and any files it refers to),
  • the expected YAML output.
A great report is a bug reproduction test

Kustomize has a simple test harness in the target package for specifying a kustomization's input and the expected output. See this example of a target test.

The pattern is

  • call NewKustTestHarness
  • specify kustomization input data (resources, patches, etc.) as inline strings,
  • call makeKustTarget().MakeCustomizedResMap()
  • compare the actual output to expected output

In a bug reproduction test, the expected output string initially contains the wrong (unexpected) output, thus unambiguously reproducing the bug.

Nearby comments should explain what the output should be, and have a TODO pointing to the related issue.

The person who fixes the bug then has a clear bug reproduction and a test to modify when the bug is fixed.

The bug reporter can then see the bug was fixed, and has permanent regression coverage to prevent its reintroduction.

Feature requests

Feature requests are welcome.

Before working on an implementation, please

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Code of conduct

Participation in the Kubernetes community is governed by the Kubernetes Code of Conduct.

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