Ignoring a field managing externally (PVC disk size ; correctly syncs but throws an error on refresh)

[multani]

We are deploying a CronJob and a PVC that the CronJob needs with Argo CD.

Sometimes, the CronJob fills up the underlying disk managed by the PVC and to prevent the job from failing, we are using an external operator to automatically increase the PVC requested size when the disk is getting full (we are using this operator: https://github.com/topolvm/pvc-autoresizer).
The operator simply changes the requested PVC disk size in the PVC resource.

When the disk size is changed, we don't commit back the new value in Argo CD, so we are seeing a drift between what we initially commited in our git repository and what is currently running. Of course, it's also not possible to shrink a PVC: as soon as the PVC has been resized by the operator, Argo CD:

1. Complains about the drift (because we don't commit back the change to git)
2. Complains that it's not possible to reduce the disk capacity

We tried to configure Argo CD to ignore this field by configuring the Argo CD Application with:

      ignoreDifferences:
        # This disk is automatically resized by the pvc-autoresizer
        - group: ""
          kind: PersistentVolumeClaim
          name: thanos-compactor
          jsonPointers:
            - /spec/resources/requests

But this only partially works:

1. We can sync the changes correctly and Argo CD:
   1. Doesn't show any OutOfSync resources anymore
   2. Can correctly sync this Application
2. However, Argo CD still shows a problem when trying to refresh the application (see below)

During refresh operations, Argo CD shows the following error message:

Failed to compare desired state to live state: failed to calculate diff: error calculating server side diff: serverSideDiff error: 
  error running server side apply in dryrun mode for resource PersistentVolumeClaim/thanos-compactor: 
    PersistentVolumeClaim "thanos-compactor" is invalid: 
      spec.resources.requests.storage: Forbidden: field can not be less than status.capacity

This is fine in the end because we can still sync the Application, but it creates confusion internally because this big visible error is fine and we need to "learn" it's OK to have it (which is not great and confuses new joiners).

Is there a way we could configure the Application so that:

1. We can initially deploy the resources using Argo CD
2. But subsequent refresh/sync are completely without errors and this particular field is completely ignored?

[duckaraptor]

What if you don't use server side diff for this application?