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Force Deletion

From v1.81, Gardener supports Shoot Force Deletion. All extension controllers should also properly support it. This document outlines some important points that extension maintainers should keep in mind to support force deletion in their extensions.

Overall Principles

The following principles should always be upheld:

  • All resources pertaining to the extension and managed by it should be appropriately handled and cleaned up by the extension when force deletion is initiated.

Implementation Details

ForceDelete Actuator Methods

Most extension controller implementations follow a common pattern where a generic Reconciler implementation delegates to an Actuator interface that contains the methods Reconcile, Delete, Migrate and Restore provided by the extension. A new method, ForceDelete has been added to all such Actuator interfaces; see the infrastructure Actuator interface as an example. The generic reconcilers call this method if the Shoot has annotation confirmation.gardener.cloud/force-deletion=true. Thus, it should be implemented by the extension controller to forcefully delete resources if not possible to delete them gracefully. If graceful deletion is possible, then in the ForceDelete, they can simply call the Delete method.

Extension Controllers Based on Generic Actuators

In practice, the implementation of many extension controllers (for example, the controlplane and worker controllers in most provider extensions) are based on a generic Actuator implementation that only delegates to extension methods for behavior that is truly provider-specific. In all such cases, the ForceDelete method has already been implemented with a method that should suit most of the extensions. If it doesn't suit your extension, then the ForceDelete method needs to be overridden; see the Azure controlplane controller as an example.

Extension Controllers Not Based on Generic Actuators

The implementation of some extension controllers (for example, the infrastructure controllers in all provider extensions) are not based on a generic Actuator implementation. Such extension controllers must always provide a proper implementation of the ForceDelete method according to the above guidelines; see the AWS infrastructure controller as an example. In practice, this might result in code duplication between the different extensions, since the ForceDelete code is usually not OS-specific.

Some General Implementation Examples

  • If the extension deploys only resources in the shoot cluster not backed by infrastructure in third-party systems, then performing the regular deletion code (actuator.Delete) will suffice in the majority of cases. (e.g - https://github.com/gardener/gardener-extension-shoot-networking-filter/blob/1d95a483d803874e8aa3b1de89431e221a7d574e/pkg/controller/lifecycle/actuator.go#L175-L178)
  • If the extension deploys resources which are backed by infrastructure in third-party systems:
    • If the resource is in the Seed cluster, the extension should remove the finalizers and delete the resource. This is needed especially if the resource is a custom resource since gardenlet will not be aware of this resource and cannot take action.
    • If the resource is in the Shoot and if it's deployed by a ManagedResource, then gardenlet will take care to forcefully delete it in a later step of force-deletion. If the resource is not deployed via a ManagedResource, then it wouldn't block the deletion flow anyway since it is in the Shoot cluster. In both cases, the extension controller can ignore the resource and return nil.