This directory holds kustomize plugins, each in its own sub-directory.

• builtin

  These are plugins written as Go plugins.

  They are converted to statically linked code in the kustomize binary by a code generator (pluginator) at kustomize build time.

  They are maintained as part of kustomize.

• someteam.example.com/v1

  Example plugins, maintained and tested by the kustomize maintainers, but not built-in to kustomize.

  Some of these might get promoted to builtin someday, as happened with the Helm Chart Inflator.

• untested/v1

  Untested, unmaintained plugins.

  These might be former examples that have been abandoned and may soon be deleted, or they might be WIP plugins that will someday become examples or builtins.

Regardless of the style used to write a plugin, it should be accompanied by a Go unit test, written using the framework maintained by the kustomize maintainers for just that purpose.

To see how this works, run any plugin test, e.g. this plugin written in bash:

pushd plugin/someteam.example.com/v1/bashedconfigmap
go test -v .
popd

For plugins with many tests, it's possible to target just one test:

pushd plugin/builtin/patchstrategicmergetransformer
go test -v -run TestBadPatchStrategicMergeTransformer PatchStrategicMergeTransformer_test.go
popd

For more discussion, see extending kustomize.

• a bare executable

  This can be anything, e.g. a shell script, a shell script that runs java in a JVM, or python in a python VM, etc. They accept a YAML stream of resources on stdin, and emit a YAML stream on stdout. They accept configuration data in a file specified as the first argument on their command line.

  If the executable is written in Go, it can take advantage of the same libraries as the kustomize builtin plugins.

• a KRM function

  These are containerized executables, that are pickier about their input. Rather than accepting a YAML stream of k8s resources, they want one ResourceList object (with the resources in that list).

• a Go plugin

  These are built as shared object libraries. Like a Go program, they're written in an unimportable main package with its own go.mod file. Go plugins cannot be reliably distributed (see docs), and are meant only as a structured way to write a builtin plugin intended for distribution with kustomize.