What does label 'topology.kubernetes.io/zone' mean for nodes without availability zone?

Question

I have a node pool WITH availability zones, and run command kubectl get nodes -o custom-columns=NAME:'{.metadata.name}',REGION:'{.metadata.labels.topology\.kubernetes\.io/region}',ZONE:'{metadata.labels.topology\.kubernetes\.io/zone}' to show nodes' zones. Values of zone label are following the format "location hyphen zone id (1, 2, 3)":
NAME REGION ZONE
aks-testpool-20035704-vmss000000 westus2 westus2-1
aks-testpool-20035704-vmss000001 westus2 westus2-2
aks-testpool-20035704-vmss000002 westus2 westus2-2
aks-testpool-20035704-vmss00000c westus2 westus2-3
aks-testpool-20035704-vmss00000d westus2 westus2-1
aks-testpool-20035704-vmss00000e westus2 westus2-3
This is detailed in doc.

For a node pool WITHOUT availability zones, all are zero. Maybe zero means "no zone".
aks-agentpool-20035704-vmss000000 westus2 0
aks-agentpool-20035704-vmss000001 westus2 0
aks-agentpool-20035704-vmss000002 westus2 0
aks-agentpool-20035704-vmss000008 westus2 0
aks-agentpool-20035704-vmss00000b westus2 0
aks-agentpool-20035704-vmss00000c westus2 0
aks-nozone-20035704-vmss000000 westus2 0
aks-nozone-20035704-vmss000001 westus2 0

But for another node pool WITHOUT availability zone:
aks-agentpool-11336751-vmss00000e westus2 4
aks-agentpool-11336751-vmss000043 westus2 3
aks-agentpool-11336751-vmss0000he westus2 2
aks-agentpool-11336751-vmss0000hu westus2 4
aks-agentpool-11336751-vmss0000k0 westus2 2
aks-agentpool-11336751-vmss0000ln westus2 0
aks-agentpool-11336751-vmss0000ox westus2 2
aks-agentpool-11336751-vmss0000r9 westus2 3
aks-agentpool-11336751-vmss0000wr westus2 1
It seems to range from 0 to 4. What do these non-zero zones mean, and are they physically separated from each other? I think this label is added by AKS, but no related document found. Thanks in advance.

Answer 1

Hello @Cheng Peng ,
Thanks for your query ! I was trying to test out with all the possible scenarios of creating AKS clusters with and with out availability zone.
If there is an availability zone , the command is displaying the zone numbers as region-1,region-2,region-3
If there is no availability zone the command is displaying the zone numbers as 0.

But we were not able to repro your scenario where it displays the numbers from 0 to 4. For sure those numbers does not indicate any thing w.r.t Zones , because for a given Azure region there will be a maximum of 3 availability zones. The only valid values while creating AKS cluster with availability zone numbers are {1,2,3}. So those numbers are certainly something else.

Do you know how the cluster mentioned in output 3 was created ?