Users should be able to pass environment variables to Kustomize

[crenshaw-dev]

Summary

The user should be able to specify environment variables to be passed to Kustomize. Plugins enable this via the spec.source.plugins.env field.

Motivation

Kustomize has some interesting features that rely on reading environment variables.

@jannfis pointed out on another issue that this could be useful.

Proposal

We could add a env field to the kustomize source. We'd want to either blocklist certain env vars (e.g. GIT_ vars) or prefix all env vars for security.

[SelfhostedPro]

The main thing I'm using in the interesting features link above is using a configmap generator from a file and not defining a value for the variable.

In the example from the documentation link above, the application.properties file would look like the following:

FOO

[maheshbaliga]

Hi @crenshaw-dev, I picked up this issue to work on and came across a Kustomize PR, which mentions that loading of the env variable when only the key is mentioned in the properties file, is a bug. It might be removed in the next major version too.

Do you have another approach in mind?

[crenshaw-dev]

Looks like the feature was removed. I think we won't be doing this. kubernetes/website#35669 (comment)