Kustomize Subcommand Integration

[shekhar-rajak]

Enhancement Description

• One-line enhancement description (can be used as a release note): Kustomize Subcommand Integration
• Kubernetes Enhancement Proposal:

[Kustomize](https://github.com/kubernetes-sigs/kustomize)
was developed as a subproject of sig-cli by kubectl maintainers to address
a collection of [issues](#motivation)) creating friction for declarative workflows in kubectl
(e.g. `kubectl apply`).  The
goal of the kustomize subproject was to bring this functionality back to kubectl to better complement
`kubectl apply` and other declarative workflow commands.

- declaratively generating Resource config
- declaratively transforming Resource config
- composing collections of Resource config across files and directories
- layering the above on top of one another

It is independent of, but complementary to, the [*server-side apply*](https://github.com/kubernetes/enhancements/issues/555)
initiative that was started later and targeted at a separate collection of
`kubectl apply` issues.

Kustomize offers generators and transformations in a declarative form that 
improve on functionality provided by existing imperative commands in kubectl.

The declarative approach offers a clear path to accountability (all input can
be kept in version control), can safely exploit a holistic, unbounded view of
disparate resources and their interdependence (it's a plan about what to do, 
not a direct action), and can be easily constrained to verifiable rules 
across this view (all edits must be structured, no removal semantics, no 
environment side-effects, etc.).

Imperative kubectl commands / flags available through kustomize:

- `kubectl create configmap`
- `kubectl create secret`
- `kubectl annotate`
- `kubectl label`
- `kubectl patch`
- `-n` (namespace)
- `-f <filename>` (kubectl processes files with lists of Resources)

Kubectl commands / flags similar to what is available through kustomize:

- `-f <dir> -R` (kubectl - recursing through directories, kustomize may follow references)
- `kubectl set image` (kustomize directive to set the image tag only, not the image)

Things in kustomize that are not imperative kubectl commands / flags:

- `namePrefix` (prepend all resource names with this)
- `nameSuffix` (append all resource names with this)
- for a limited set of fields allow one field value to be set to match another

• Discussion Link:
• Primary contact (assignee): @Liujingfang1 @liggitt @seans3 @soltysh
• Responsible SIGs: sig-cli
• Enhancement target (which target equals to which milestone):
  • Alpha release target (x.y):
  • Beta release target (x.y):
  • Stable release target (x.y):
• Alpha
  • KEP (k/enhancements) update PR(s):
  • Code (k/k) update PR(s):
  • Docs (k/website) update PR(s):

Please keep this description up to date. This will help the Enhancement Team to track the evolution of the enhancement efficiently.

[shekhar-rajak]

#2378 created for migrating the old keps into new template.

[soltysh]

/sig cli
/assign

[fejta-bot]

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Mark the issue as fresh with /remove-lifecycle stale.
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If this issue is safe to close now please do so with /close.

Send feedback to sig-contributor-experience at kubernetes/community.
/lifecycle stale

[soltysh]

This was needed for KEP migration, but the mechanism is already completed.
/close

[k8s-ci-robot]

@soltysh: Closing this issue.

In response to this:

This was needed for KEP migration, but the mechanism is already completed and GA.
/close

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