Using Finalizers

Finalizers allow controllers to implement asynchronous pre-delete hooks. Let’s say you create an external resource (such as a storage bucket) for each object of your API type, and you want to delete the associated external resource on object’s deletion from Kubernetes, you can use a finalizer to do that.

You can read more about the finalizers in the Kubernetes reference docs. The section below demonstrates how to register and trigger pre-delete hooks in the Reconcile method of a controller.

The key point to note is that a finalizer causes “delete” on the object to become an “update” to set deletion timestamp. Presence of deletion timestamp on the object indicates that it is being deleted. Otherwise, without finalizers, a delete shows up as a reconcile where the object is missing from the cache.


  • If the object is not being deleted and does not have the finalizer registered, then add the finalizer and update the object in Kubernetes.
  • If object is being deleted and the finalizer is still present in finalizers list, then execute the pre-delete logic and remove the finalizer and update the object.
  • Ensure that the pre-delete logic is idempotent.
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First, we start out with some standard imports. As before, we need the core controller-runtime library, as well as the client package, and the package for our API types.

package controllers

import (

	ctrl ""

	batchv1 ""

By default, kubebuilder will include the RBAC rules necessary to update finalizers for CronJobs.


The code snippet below shows skeleton code for implementing a finalizer.

func (r *CronJobReconciler) Reconcile(ctx context.Context, req ctrl.Request) (ctrl.Result, error) {
	log := r.Log.WithValues("cronjob", req.NamespacedName)

	cronJob := &batchv1.CronJob{}
	if err := r.Get(ctx, req.NamespacedName, cronJob); err != nil {
		log.Error(err, "unable to fetch CronJob")
		// we'll ignore not-found errors, since they can't be fixed by an immediate
		// requeue (we'll need to wait for a new notification), and we can get them
		// on deleted requests.
		return ctrl.Result{}, client.IgnoreNotFound(err)

	// name of our custom finalizer
	myFinalizerName := ""

	// examine DeletionTimestamp to determine if object is under deletion
	if cronJob.ObjectMeta.DeletionTimestamp.IsZero() {
		// The object is not being deleted, so if it does not have our finalizer,
		// then lets add the finalizer and update the object. This is equivalent
		// to registering our finalizer.
		if !controllerutil.ContainsFinalizer(cronJob, myFinalizerName) {
			controllerutil.AddFinalizer(cronJob, myFinalizerName)
			if err := r.Update(ctx, cronJob); err != nil {
				return ctrl.Result{}, err
	} else {
		// The object is being deleted
		if controllerutil.ContainsFinalizer(cronJob, myFinalizerName) {
			// our finalizer is present, so lets handle any external dependency
			if err := r.deleteExternalResources(cronJob); err != nil {
				// if fail to delete the external dependency here, return with error
				// so that it can be retried.
				return ctrl.Result{}, err

			// remove our finalizer from the list and update it.
			controllerutil.RemoveFinalizer(cronJob, myFinalizerName)
			if err := r.Update(ctx, cronJob); err != nil {
				return ctrl.Result{}, err

		// Stop reconciliation as the item is being deleted
		return ctrl.Result{}, nil

	// Your reconcile logic

	return ctrl.Result{}, nil

func (r *Reconciler) deleteExternalResources(cronJob *batch.CronJob) error {
	// delete any external resources associated with the cronJob
	// Ensure that delete implementation is idempotent and safe to invoke
	// multiple times for same object.