init

kubebuilder init --domain tutorial.kubebuilder.io --repo github.com/denis-zakharov/kubebuilder-cron --project-name=kubebuilder-cron

A domain is an API domain. An API group corresponds to a subdomain.

k8s api

• group: a collection of related functionality.
• version: each group has one or more versions.
• kind: each group-version contains one or more API types (Kind or a GroupVersionKind or a GVK).
• resource: a use of a Kind in the API (an object manifest or a GroupVersionResource or a GVR).

The resources are always lowercase, and by convention are the lowercase form of the Kind.

Each GVK corresponds to a given root Go type in a package.

The Scheme maps Go types to corresponding GVK types.

adding a new api

kubebuilder create api --group batch --version v1 --kind CronJob

groupversion_info.go has a GV info GroupVersion{Group: "batch.tutorial.kubebuilder.io", Version: "v1"}.

cronjob_types.go has a Kind: CronJob Go types. The corresponding generator marker is +kubebuilder:object:root:

• metav1.TypeMeta: kind and version.
• metav1.ObjectMeta metadata like name, labels and namespace.
• Spec is a desired state.
• K8s reconciles the desired state with an observed state on the cluster and any other external state, and then records what it observed as a Status.

Spec and Status are subjects for implementation.

The object generator generates an implementation of the runtime.Object interface for us, which is the standard interface that all types representing Kinds must implement.

Finally, we add the Go types to the API group. This allows us to add the types in this API group to any Scheme.

func init() {
    SchemeBuilder.Register(&CronJob{}, &CronJobList{})
}

defining an api

All serialized fields must be camelCase.

Type coversions:

• primitives
• numbers: int32 and int64
• decimals: resource.Quantity (like 100m, 100Mi, 1M).
• time: metav1.Time.

controller

Each controller focuses on one root Kind but may interact with other Kinds.

A controller implements sigs.k8s.io/controller-runtime/pkg/reconcile.Reconciler interface:

type Reconciler interface {
	// Reconciler performs a full reconciliation for the object referred to by the Request.
	// The Controller will requeue the Request to be processed again if an error is non-nil or
	// Result.Requeue is true, otherwise upon completion it will remove the work from the queue.
	Reconcile(context.Context, Request) (Result, error)
}

webhooks

kubebuilder create webhook --group batch --version v1 --kind CronJob --defaulting --programmatic-validation

make manifests

deploy

make docker-build docker-push IMG=zadenis/cronjob-controller:v0.1
make deploy IMG=zadenis/cronjob-controller:v0.1