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3fe047f Oct 10, 2018
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Eschewed Features

For a bigger picture about why kustomize does some things and not others, see the glossary entry for DAM.

Removal directives

kustomize supports configurations that can be reasoned about as compositions or mixins - concepts that are widely accepted as a best practice in various programming languages.

To this end, kustomize offers various addition directives. One can add labels, annotations, patches, resources and bases. Corresponding removal directives are not offered.

Removal semantics would introduce many possibilities for inconsistency, and the need to add code to detect, report and reject it. It would also allow, and possibly encourage, unnecessarily complex configuration layouts.

When faced with a situation where removal is desirable, it's always possible to remove things from a base like labels and annotations, and/or split multi-resource manifests into individual resource files - then add things back as desired via the kustomization.

If the underlying base is outside of one's control, an OTS workflow is the recommended best practice. Fork the base, remove what you don't want and commit it to your private fork, then use kustomize on your fork. As often as desired, use git rebase to capture improvements from the upstream base.

Build-time side effects from CLI args or env variables

kustomize supports the best practice of storing one's entire configuration in a version control system.

Changing kustomize build configuration output as a result of additional arguments or flags to build, or by consulting shell environment variable values in build code, would violate that goal.

kustomize insteads offers kustomization file edit commands. Like any shell command, they can accept environment variable arguments.

For example, to set the tag used on an image to match an environment variable, run

kustomize edit set imagetag nginx:$MY_NGINX_VERSION

as part of some encapsulating work flow executed before kustomize build.

Globs in kustomization files

kustomize supports the best practice of storing one's entire configuration in a version control system.

Globbing the local file system for files not explicitly declared in the kustomization file at kustomize build time would violate that goal.

Allowing globbing in a kustomization file would also introduce the same problems as allowing globbing in java import declarations or BUILD/Makefile dependency rules.

kustomize will instead provide kustomization file editting commands that accept globbed arguments, expand them at edit time relative to the local file system, and store the resulting explicit names into the kustomization file.

In this way the resources, patches and bases used at build time remain explicitly declared in version control.