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RomanAleksejuk-7395 asked FrancescoRestelli-0037 answered

AKS nodepool scaleset fault domains count is always 1, why? Are there any ways to change that?

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):

70269-xtaqw.png

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.




azure-kubernetes-serviceazure-virtual-machines-scale-set
xtaqw.png (228.5 KiB)
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Hello, Thank you for reaching out. I am looking into this issue and will get back to you asap. Thank you

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Monalla-MSFT avatar image
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Monalla-MSFT answered Monalla-MSFT commented

Hello @RomanAleksejuk-7395 - Thanks for reaching out.

I was able to reproduce and am looking into the source of the fault domain count not being 5. I have reached out to Engineering team and I will get back to you as soon as I have an update from them. Thank you for your patience.

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@Monalla-MSFT Can it be related to the documentation - https://docs.microsoft.com/en-us/azure/virtual-machine-scale-sets/virtual-machine-scale-sets-manage-fault-domains which says:

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.

But this statement from the doc condratics the fact, that you can perfectly deploy a separate scaleset (apart from AKS deployment) configure the availability zones and have a 5update/fault domain in each availability zone. So when deploying the scaleset separately - it is ok, when deploying as part of the AKS - then Update/fault domains count is always 1.

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It could be. Let me check that with our Engineering team here and get back to you as soon as possible. Thank you for your patience.

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mwithrow avatar image
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mwithrow answered

AKS does not use Fault domains. You just need to ensure multiple nodes for non-zone and multiple zones for zonal.

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FrancescoRestelli-0037 avatar image
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FrancescoRestelli-0037 answered

hi,

Can someone elaborate more on this topic? Why should it not be important to spread accross fault domain?

What does "AKS does not use Fault domains" mean?

Even when adding an additional "user" scaleset pool to an existing aks cluster using the portal, the new scaleset is created with 1 fault domain!

So is it not recommended using scalesets at this point?

thank you br francesco

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