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When deploying AKS cluster into different availability zones ("1,2,3" in our case) the vm scaleset is used for default nodepool deployment (not availability set). Everything is pretty fine there, but the problem is - while using the default nodepool scaleset, it is put into 1 fault domains only, and i did not find a way to change that (despite the fact, that the vm scaleset should be deployed into 5 fault/update domains as per documentation):

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Why is it so ? How to put the nodepool into default 5 fault/update domains in addition to 3 availability zones (i mean 5 fault/update domains in each of the 3 availability zones)?

P.S. - You can always deploy AKS cluster's nodepool into availabilitySet, and have 5 update/fault domains, but then the availability zones are not available when using the availabilitySet.

Edward Han-MSFT
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misfit
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  • I wonder about are update domains coordinated across availability zones or are you just taking a chance that the updates would not happen at the same times in different zones? Availability set would be more important to coordinate for a website (more important than autoscaling) if you ask me. – Richard Sep 06 '22 at 19:35

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By reference to this doc: Choosing the right number of fault domains for virtual machine scale set, for the regions that support zonal deployment of virtual machine scale sets and this option is selected, the default value of the fault domain count is 1 for each of the zones.

You can also consider aligning the number of scale set fault domains with the number of Managed Disks fault domains.

wallezzi
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  • Thanks, i've seen this doc you are refering to, but the problem is - you can't change this (fault domain count is strictly 1). If you create just the vm scaleset (separate deployment without aks) with zonal deployment - then you can see 5 fault domain (despite the fact, that the docs are saying it should be 1). But if the vm scaleset is a part of AKS deployment - then it is strictly 1 and there are no way to change it. – misfit Feb 22 '21 at 07:47
  • Agree with you. You could submit feedback for this documentation here: https://github.com/MicrosoftDocs/azure-docs/issues, so the doc author can review your feedback and update it correspondingly. – wallezzi Feb 22 '21 at 08:03