Invoke ruby method when storage domain free space (rhv) or datastore (vmware) change

we have combined the functionality of manageiq and servicenow.
Now we exhibit catalog items from cloudforms that are ordered by servicenow.
we used also a control policy (and a ruby method) to push data concerning the VMs to the servicenow cmdb.
in this way when a vm change it’s settings, the data is updated on the servicenow cmdb.

we would also like to achieve the same result with regard to infrastructure provider data.
For example we would like to notify the remaining space on datastore (vmware) or storage domain (rhv) when space is consumed (for example when we create vm or extending existing vm disks).

In few words:
We have already written a ruby method that push data that we need (thanks to object walker), but now we need a way to call that method automatically when the storage decrease.

Do you have any ideas for doing this?

Thanks in advance