Server-Side Apply: ExtractPod should specify UID

[gnuletik]

TLDR

When using server side apply with ExtractPod, a controller may recreate a resource that was deleted by attempting to remove a finalizer.

Context

I have a controller that watches pods to remove finalizer using Server-Side Apply (to avoid race condition between controllers as suggested here).

It removes the finalizer in the following way:

podApplyConfig, err := coreac.ExtractPod(pod, fm)
if err != nil {
        return fmt.Errorf("coreac.ExtractPod: %w", err)
}

// updating something
podApplyConfig.Finalizers = nil

_, err = w.client.CoreV1().Pods(ns).Apply(ctx, podApplyConfig, meta.ApplyOptions{FieldManager: smtg})
if err != nil {
        return fmt.Errorf("client.Apply: %w", err)
}

The SharedInformer sometimes sends the event multiple times, which leads to pod being recreated after deletion, given this scenario:

• api-server: sets deletionTimestamp
• my-controller: receives Update event: it removes the finalizer with SSA
• api-server: deleted the pod
• my-controller: receives a duplicated Update event: it removes the finalizer a second time with SSA
• api-server: creates a pod instead of updating it

Fix

Kubernetes specs specify that:

Create is blocked on apply if uid is provided link

See KEPS

We can manually call podApply := podApply.WithUID(pod.UID) to workaround this.

However, I think that it would be better that ExtractPod (and similar method for other resources) sets the UID before returning it.

client-go/applyconfigurations/core/v1/pod.go

Lines 72 to 84 in aa7909e

	func extractPod(pod *apicorev1.Pod, fieldManager string, subresource string) (*PodApplyConfiguration, error) {
	b := &PodApplyConfiguration{}
	err := managedfields.ExtractInto(pod, internal.Parser().Type("io.k8s.api.core.v1.Pod"), fieldManager, b, subresource)
	if err != nil {
	return nil, err
	}
	b.WithName(pod.Name)
	b.WithNamespace(pod.Namespace)
	b.WithKind("Pod")
	b.WithAPIVersion("v1")
	return b, nil
	}

WDYT?

I can make a PR if that sounds good to you.
However, this part of the codebase seems to be generated, so I'd need a hint on where to edit that.

Thanks!