Azure-docs: Behavior when --platform-fault-domain-count option is not used in az vmss create command

[kogesaka]

Hi Experts,

The description in the Azure CLI section says "You can set the parameter --platform-fault-domain-count to 1, 2, or 3 (default of 5 if not specified).". But when without --platform-fault-domain-count option az vmss create command executing, the value of "platformFaultDomainCount" was not set from Azure Resource Explorer.

Is this behavior expected?

The executed command is as follows:
az vmss create --resource-group <Resource Group name> --name <VMSS name> --image UbuntuLTS --upgrade-policy-mode automatic --admin-username <user name> --generate-ssh-keys --single-placement-group false

When creating the VMSS from the Azure portal, the following settings were set to ""platformFaultDomainCount" : 5".

• Enable scaling beyond 100 instances : yes
• Spreading algorithm : Fixed spreading (not recommended with zones)

Best Regards,

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Document Details

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• ID: 6a729a8a-23ea-094d-b96a-cb628832f730
• Version Independent ID: 6bed91cd-1519-032d-e589-8ea826aa8b50
• Content: Manage fault domains in Azure virtual machine scale sets
• Content Source: articles/virtual-machine-scale-sets/virtual-machine-scale-sets-manage-fault-domains.md
• Service: virtual-machine-scale-sets
• GitHub Login: @rajsqr
• Microsoft Alias: drewm

[msrini-MSFT]

@kogesaka , Thank you for your feedback. We will investigate and get back to you shortly.

[Karishma-Tiwari-MSFT]

@mayanknayar I am also seeing the same.
When I create the VMSS using portal, I can see this in activity log:

But --platform-fault-domain-count does not show up for VMSS created via Azure CLI, in activity log.
Can you please help us confirm on this behavior? Thanks :)

[Karishma-Tiwari-MSFT]

@mayanknayar Did you get a chance to take a look at the customer's question. Need your help with the confirmation. Thanks. :)

[mayanknayar]

The platform fault domain count will default to 5, whenever a value has not been specified. It is possible that CLI is not showing the count as a return response, but the count would have been set. Please check with a GET on the VMSS.

[Karishma-Tiwari-MSFT]

@kogesaka Please try the suggestion shared above and share the results.
https://docs.microsoft.com/en-us/powershell/module/azurerm.compute/get-azurermvmss?view=azurermps-6.13.0

[kogesaka]

Hi, @mayanknayar @Karishma-Tiwari-MSFT ,

I checked using Get-AzVmss, but there was no PlatformFaultDomainCount item.
It seems that it is not displayed unless it is created by Azure portal or "az vmss create" command with "--platform-fault-domain-count" option.

[Karishma-Tiwari-MSFT]

Thanks @kogesaka
@mayanknayar Thanks for sharing your inputs. Can you please help confirm on this behavior. Thanks :)

Hi, @mayanknayar @Karishma-Tiwari-MSFT ,

I checked using Get-AzVmss, but there was no PlatformFaultDomainCount item.
It seems that it is not displayed unless it is created by Azure portal or "az vmss create" command with "--platform-fault-domain-count" option.

[mayanknayar]

@Karishma-Tiwari-MSFT - this needs to be raised with the CLI team. Please start a thread with the CLI team

[Karishma-Tiwari-MSFT]

I am closing this issue and opening a issue with Azure CLI team.
Thanks for bringing this to our attention. We will now close this issue. If there are further questions regarding this matter, please tag me in a comment. I will reopen it and we will gladly continue the discussion.