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.

Highlights:

• 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.

{{#literatego ../cronjob-tutorial/testdata/finalizer_example.go}}