Make `patch` fail on "create"

Eschewed features

[X] This issue is not requesting templating, unstuctured edits, build-time side-effects from args or env vars, or any other eschewed feature.

What would you like to have added?

A kustomize patch can result into an "update" or a "create". It depends.

Example of a kustomize patch:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: foo
  namespace: foo-system
spec:
  template:
    spec:
      containers:
      - name: backend
        image: ghcr.io/foo/bar

there are two cases: there is already a container with name "backend", or there is no such container.

As an author of the kustomize patch, I want always to do an update.

Is there a way to get an error from kustomize if the patch would do a "create"?

Background: Names got changed, and then we had two containers in the deployment, because one place was not updated. I would like this to fail early the next time.

Why is this needed?

I don't want two containers in my deployment. I want to update an existing deployment.

Can you accomplish the motivating task without this feature, and if so, how?

I could use json-patch with "replace". But this is hard to read and write.

What other solutions have you considered?

Anything else we should know?

No response

Feature ownership

[X] I am interested in contributing this feature myself! 🎉

kubernetes-sigs / kustomize