Inconsistent topology.kubernetes.io/zone label naming

Question

Hi there,

We have an issue with inconsistent label naming in our AKS clusters - the topology.kubernetes.io/zone label. We are scraping data from our AKS clusters for further internal operations but we had some issues caused by inconsistent naming of that label and we have observed the following behavior.

According to the documentation we have observed in some of the clusters with zoned nodes, the label value is <region>-<AZ>, e.g. centralus-1, where AZ reflects the availability zone in which the node is deployed so its value is in the range 1-3.

For unzoned nodes, the value is supposed to be equal to the faultDomain- 0. In different clusters with unzoned nodes, we have observed this label being set to a number in the range 0-4.

Could you please explain to us why in some of the scenarios topology.kubernetes.io/zone is set to a number 1-4 where according to the docs it should be equal to 0? Also according to the documentation for a given Azure region, there will be a maximum of 3 availability zones so what does this number 4 mean?

Best regards and thank you in advance!