kustomize

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 edited text.

This tool is sponsored by sig-cli (KEP).

kubectl integration

To find the kustomize version embedded in recent versions of kubectl, run kubectl version:

> kubectl version --short --client
Client Version: v1.26.0
Kustomize Version: v4.5.7

The kustomize build flow at v2.0.3 was added
to kubectl v1.14. The kustomize
flow in kubectl remained frozen at v2.0.3 until kubectl v1.21,
which updated it to v4.0.5. It will
be updated on a regular basis going forward, and such updates
will be reflected in the Kubernetes release notes.

Kubectl version	Kustomize version
< v1.14	n/a
v1.14-v1.20	v2.0.3
v1.21	v4.0.5
v1.22	v4.2.0

For examples and guides for using the kubectl integration please
see the kubernetes documentation.

Usage

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.

File structure:

~/someApp
├── 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.

File structure:

~/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

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, referring 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 -

Community

Code of conduct

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

rybnico/kustomize