in controller.go [321:333]
func (c *Controller) updateFooStatus(foo *samplev1alpha1.Foo, deployment *appsv1.Deployment) error {
// NEVER modify objects from the store. It's a read-only, local cache.
// You can use DeepCopy() to make a deep copy of original object and modify this copy
// Or create a copy manually for better performance
fooCopy := foo.DeepCopy()
fooCopy.Status.AvailableReplicas = deployment.Status.AvailableReplicas
// If the CustomResourceSubresources feature gate is not enabled,
// we must use Update instead of UpdateStatus to update the Status block of the Foo resource.
// UpdateStatus will not allow changes to the Spec of the resource,
// which is ideal for ensuring nothing other than resource status has been updated.
_, err := c.sampleclientset.SamplecontrollerV1alpha1().Foos(foo.Namespace).UpdateStatus(context.TODO(), fooCopy, metav1.UpdateOptions{})
return err
}