Generators on Component Operator Runtime

Transforming Existing Generators

Mon, 01 Jan 0001 00:00:00 +0000

Sometimes it is desirable to reuse an existing generator, but adjust its input (the parameters passed to the generation step) or its output (the object manifests it returns) — for example to inject computed values, or to patch rendered objects. This is done by wrapping any Generator into a TransformableGenerator:

package manifests

// Interface for generators that can be enhanced with parameter/object transformers.
type TransformableGenerator interface {
	Generator
	WithParameterTransformer(transformer ParameterTransformer) TransformableGenerator
	WithObjectTransformer(transformer ObjectTransformer) TransformableGenerator
}

// Wrap an existing generator into a TransformableGenerator.
func NewGenerator(generator Generator) TransformableGenerator

Transformers are attached through the fluent WithParameterTransformer() and WithObjectTransformer() methods (which return the generator again, so calls can be chained). Multiple transformers of each kind can be attached and are applied in order. The transformation logic itself is provided by implementing:

Helm Generator

Mon, 01 Jan 0001 00:00:00 +0000

If a component already has a productive Helm chart, the HelmGenerator implementation (package pkg/manifests/helm) can render it:

package helm

func NewHelmGenerator(fsys fs.FS, chartPath string, clnt client.Client) (*HelmGenerator, error)

fsys must be an fs.FS implementation (such as an embed.FS), or nil. If nil, all file operations are performed on the OS filesystem, and chartPath may be an absolute path or a path relative to the controller’s working directory. If fsys is non-nil, chartPath should be relative (an absolute path is turned into a relative one by stripping the leading slash). When using a real filesystem, os.Root.FS() is recommended over os.DirFS() in order to fence symbolic links. An empty chartPath is treated like ..
clnt is deprecated and ignored; it will be removed in a future release. The clients used at generation time are taken from the context instead.

Transformable variants are available as NewTransformableHelmGenerator(), NewHelmGeneratorWithParameterTransformer(), and NewHelmGeneratorWithObjectTransformer() (see Transforming Existing Generators).

Kustomize Generator

Mon, 01 Jan 0001 00:00:00 +0000

The KustomizeGenerator (package pkg/manifests/kustomize) renders the component’s resources from a given kustomization. As a special case, one or more plain Kubernetes manifests (without a kustomization.yaml) are supported as well. In addition, all (or selected) files in the kustomization directory can be templatized in a Helm-ish way: they are treated as a common template group, and the well-known template function set available in Helm can be used — that is, all sprig functions, plus functions like include, tpl, lookup, and the following: