Should we use DeepCopy() to update Spec?

[hatrena]

Hi,

I am new to Kubebuilder, so the question is "Should I use DeepCopy() to update the object's Spec?". if so, why?

sample code:

objToUpdate := obj.DeepCopy()
objToUpdate.Spec.Foo = "bar"

err := r.Client.Patch(ctx, objToUpdate, client.MergeFrom(obj))
if err != nil {
return ctrl.Result{}, fmt.Errorf("error on patch obj %w", err)
}

[FillZpp]

This is not necessary. Only note that both Update and Patch methods will overwrite the new object returned from APIServer into the given object, which means the objToUpdate will be changed to the latest object after patched successfully.

So, you should DeepCopy it only if you don't want the original object to be modified.

[hatrena]

Got it. Thank you so much.

[hatrena]

So everything is clear. I have tested it and watched resourceVersion of the object. With DeepCopy() the original object (in the code) doesn't get modified (but it has updated in etcd as resourceVersion increased).

So in what cases I don't need the original to get updated in my code? Do you have any example scenarios?

I appreciate your help

[FillZpp]

So in what cases I don't need the original to get updated in my code? Do you have any example scenarios?

If you ever read the KCM code, you may find those built-in controllers always deep copy objects before modify them. That's because those objects are references that listed from Informer directly, which means modify them will lead to the objects in Informer cache been changed unexpectedly.

But controller-runtime, on the other hand, will deep copy objects before returning them to List method by default, which means the objects you listed are already deep copied. So you can directly pass them into Update or Patch, unless you have used the UnsafeDisableDeepCopyByObject option to disable the default DeepCopy for List operation.

https://github.com/kubernetes-sigs/controller-runtime/blob/15154aaa67679df320008ed45534f83ff3d6922d/pkg/cache/cache.go#L126-L130

[camilamacedo86]

Closing since it is answered.