apimachinery.ExtractInto generates diff

[gnuletik]

When creating a pod:

• with server-side apply
• with an empty affinity

pod := coreac.Pod(name, ns).
    WithSpec(
        coreac.PodSpec().
        coreac.WithAffinity(coreac.Affinity()) // notice the empty affinity value here
        // other spec values omitted for brevity
    )

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

When trying to later update it by using ExtractPodInfo:

pod, err = w.client.CoreV1().Pods(ns).Get(ctx, podName, meta.GetOptions{})
if err != nil {
        return fmt.Errorf("client.Get: %w", err)
}

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 Apply operation fails with the following error:

If the object is empty, we avoid setting an empty affinity, which leads to issue
while patching the pod later.

client.Apply: Pod "pod-name" is invalid: spec: Forbidden: pod updates may not change fields other than `spec.containers[*].image`,`spec.initContainers[*].image`,`spec.a
ctiveDeadlineSeconds`,`spec.tolerations` (only additions to existing tolerations),`spec.terminationGracePeriodSeconds` (allow it to be set to 1 if it was previously negative)
core.PodSpec{
      ... // 15 identical fields
      Subdomain:         "",
      SetHostnameAsFQDN: nil,
-    Affinity:          &core.Affinity{},
+    Affinity:          nil,
      SchedulerName:     "default-scheduler",
      ... // 13 identical fields
}

Using k8s.io/client-go v0.28.8

This can be fixed by setting the affinity to nil when creating the pod (instead of setting the zero-value).
However, I'm wondering if this should be handled by client-go (this seems to be implemented in apimachinery).

What do you think?

[crudbetter]

I've been keen to learn Go and more about Kubernetes - so challenged myself to put together a reproduction of this.

How do we progress to getting an opinion on whether there is anything to fix in client-go? @liggitt you seem active in this project recently - any ideas? Is this issue raised in the wrong project?