Maximizing Availability Set Fault Domains in ARM Templates

AZ-104 By islever Editorial Last updated

Automate deployment of resources by using Azure Resource Manager (ARM) templates or Bicep files Create and configure virtual machines

Short answer

D Configure platformFaultDomainCount to the maximum value so the availability set spreads the VMs across the most fault domains, maximizing survival during fabric failure.

Question

Your company has an Azure subscription.
You need to deploy a number of Azure virtual machines (VMs) using Azure Resource Manager (ARM) templates. You have been informed that the VMs will be
included in a single availability set.
You are required to make sure that the ARM template you configure allows for as many VMs as possible to remain accessible in the event of fabric failure or
maintenance.
Which of the following is the value that you should configure for the platformFaultDomainCount property?
  1. 10
  2. 30
  3. Min Value
  4. Max Value Correct Answer

Key Takeaways

The question tests understanding that a higher fault domain count spreads VMs across more independent hardware racks, and the trap is picking a hardcoded number like 3 or 30 instead of the intended answer, Max Value.

When deploying Azure VMs into an availability set via an ARM template, the platformFaultDomainCount property controls how many fault domains the VMs are spread across. To keep as many VMs running during a fabric failure or planned maintenance, you set this property to the maximum value supported by the region.

Common mistake: Choosing a literal number such as 3 (or picking Min Value) because the documentation caps fault domains at 3 in most regions; however, the exam expects the property to be set to the largest value the platform accepts, since spreading VMs across more fault domains improves resiliency.

Expert Analysis

Why the Answer Is Correct

The platformFaultDomainCount property determines how many fault domains — groups of VMs sharing a common power source and network switch — the availability set uses. Setting it to the maximum supported value distributes VMs across the greatest number of physically separate hardware stacks, so a single rack-level failure or maintenance event takes down the fewest VMs. That directly satisfies the requirement that "as many VMs as possible remain accessible in the event of fabric failure or maintenance," which is the stated design goal. Because the maximum differs by region (commonly 2 or 3, and up to 5 in some regions), the template should express this as the maximum value rather than a hardcoded number. Azure supports an extended availability set option with up to 20 fault domains, reinforcing that higher counts equal better fault tolerance.

Why the Other Options Are Wrong

Option A (10) is an arbitrary number that exceeds the fault domain cap in most regions and provides no basis in the requirement. Option B (30) is well beyond any supported fault domain count and is not a valid configuration. Option C (Min Value) would collapse the availability set onto as few fault domains as possible, meaning a single rack failure could take down most or all of the VMs — the exact opposite of the resiliency goal. Options A and B look plausible only because the fault domain maximum can vary, but neither matches the exam's intent of choosing the largest allowed value.

Community Comment Notes

The community largely converges on D. As maqibali explained, "The platformFaultDomainCount property specifies the number of fault domains to be used by the availability set." ppp131176 concurred, noting "D is correct. 2 or 3 is max for a region so answer should be Max." jairoaquinterov observed that "Each availability set can be configured with up to 3 fault domains and 20 update domains. However 20 is not in options, the correct answer is D." The lone dissenting voice, Sahar_A, argued the maximum is 3 and favored a numeric choice, but that reasoning still supports selecting the maximum rather than a minimum or arbitrary value — so D remains the best answer.

Official Reference

These links open the official vendor documentation in a new tab.

Exam Strategy

Read whether the question asks for a maximum, minimum, or specific numeric property value, then match it to the resiliency goal described. For availability sets, more fault domains always means better fault tolerance, so choose the option representing the largest supported count — here, Max Value.

Frequently Asked Questions

Why is Max Value correct when fault domains are capped at 2 or 3 per region?

The maximum varies by region, so the template must express the intent of using the largest supported value. A hardcoded 3 could be invalid in regions limited to 2.

How many fault domains can an availability set actually have in Azure?

Standard availability sets support up to 3 fault domains in most regions (2 in some), while extended availability sets support up to 20. Update domains max out at 20.

More AZ-104 FAQ →

Discussion 41 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 30 of 41

  1. maqibali 👍 44 Answered D
    The platformFaultDomainCount property specifies the number of fault domains to be used by the availability set. A fault domain is a group of underlying hardware resources in a data center that share a common power source and network switch, but are physically separated from each other. By distributing virtual machines across fault domains, you can ensure that no single point of failure can take down all of the virtual machines at once. In Azure, the maximum value for platformFaultDomainCount is 3. This means that an availability set can have up to 3 fault domains. The minimum value for platformFaultDomainCount is 1. To make sure that the ARM template allows for as many VMs as possible to remain accessible in the event of fabric failure or maintenance, you should set the platformFaultDomainCount property to its maximum value of 3. So the correct answer is: D. Max Value
  2. ppp131176 👍 33
    D is correct. 2 or 3 is max for a region so answer should be Max.
  3. Mazinger 👍 5
    When deploying Azure virtual machines within an availability set using ARM templates, the platformFaultDomainCount property should be set to a value that allows for as many VMs as possible to remain accessible in the event of fabric failure or maintenance. The platformFaultDomainCount property defines the number of fault domains used within the availability set. Each fault domain represents a group of Azure infrastructure that can potentially fail together. By default, Azure uses three fault domains for each availability set. To ensure maximum availability, you should set the platformFaultDomainCount property to the maximum value of 3. This will ensure that each VM is placed in a different fault domain, allowing them to remain accessible in the event of a fault domain failure. Therefore, the correct option is D. Max Value.
  4. jairoaquinterov 👍 4 Answered D
    Each virtual machine in your availability set is assigned an update domain and a fault domain by the underlying Azure platform. Each availability set can be configured with up to 3 fault domains and 20 update domains. However 20 is not in options, the correct answer is D
  5. Rohithalkt 👍 4
    Correct. Should be D
Show 25 more comments
  1. Timock 👍 3
    Each virtual machine in your availability set is assigned an update domain and a fault domain by the underlying Azure platform. Each availability set can be configured with up to three fault domains and twenty update domains. With CLI the platform fault domain count will default to 5 whenever a value has not been specified. Now if they are stating the parameter accepts MAX or MIN this appears incorrect. The maximum according to the listings below are 3 and there are no MAX/MIN parameters as an option. But if they mean choose the max amount after you find out.... then yes the answer is Max Value. Seems best to just not to put a number and it should default to 5.
  2. pc1707 👍 3 Answered D
    @mattpaul why are you creating a new a public community thread.com and that too a paid version? please join us here provide your feedback for free.
  3. Sahar_A 👍 3 Answered C
    The maximum value for the platformFaultDomainCount property in an Azure Availability Set is 3.
  4. Mehedi007 👍 3 Answered D
    "Each availability set can be configured with up to 3 fault domains and 20 update domains."
  5. Yuraq 👍 2
    Each availability set can be configured with up to 3 fault domains and 20 update domains. https://learn.microsoft.com/en-us/azure/virtual-machines/availability-set-overview You can set the property properties.platformFaultDomainCount to 1, 2, or 3 (default of 3 if not specified) https://learn.microsoft.com/en-us/azure/virtual-machine-scale-sets/virtual-machine-scale-sets-manage-fault-domains D is the most sensible answer.
  6. monisshk 👍 2 Answered D
    To ensure that as many VMs as possible remain accessible in the event of fabric failure or maintenance, you should configure the platformFaultDomainCount property to the maximum value. Therefore, the correct answer is: D. Max Value This setting helps distribute the VMs across multiple fault domains, reducing the risk of simultaneous failures.
  7. MCLC2021 👍 2
    CORRECT ANSWER D (Max Value) You can set the property properties.platformFaultDomainCount to 1, 2, or 3 (default of 1 if not specified). https://learn.microsoft.com/en-us/azure/virtual-machine-scale-sets/virtual-machine-scale-sets-manage-fault-domains
  8. chaudha4 👍 2
    The question does not say that the max and min values are defined anywhere. Is this question missing some additional information regarding the ARM templates ? Based on the information provided, none of the options are correct.
  9. fiahbone 👍 2 Answered D
    Max value,since 3 is the max platformFaultDomainCount for availability sets. https://learn.microsoft.com/en-us/azure/virtual-machines/availability-set-overview
  10. c7d45f4 👍 2 Answered D
    the answer is D
  11. jhothanan 👍 2 Answered D
    D es correcto
  12. Bikth 👍 1 Answered D
    The platformFaultDomainCount property in an Azure Availability Set specifies the number of fault domains for the virtual machines. Fault domains are essentially physical groupings of resources that provide isolation from hardware failures, power outages, or network issues. Azure allows for a maximum of 3 fault domains in most regions (and up to 2 fault domains in some regions like classic cloud regions). Configuring the maximum value ensures that VMs are distributed across the greatest number of fault domains possible, maximizing their availability during fabric failures or maintenance events. Key Notes: Min Value: Would reduce fault tolerance, as all VMs could end up in a single fault domain. Max Value: Ensures the highest fault tolerance by spreading VMs across all available fault domains. 10 and 30: These values are not valid, as the maximum fault domain count is 3 in Azure (or 2 in specific regions).
  13. KangID 👍 1
    According to question that "configure allows for as many VMs as possible to remain accessible" You need to set Max value in platformFaultDomainCount. You can use The command in this Microsoft article (https://learn.microsoft.com/en-us/azure/virtual-machines/availability-set-overview) "Availability sets overview" to retrieves a list of fault domains per region. az vm list-skus --resource-type availabilitySets --query '[?name==Aligned].{Location:locationInfo[0].location, MaximumFaultDomainCount:capabilities[0].value}' -o Table
  14. LaReis 👍 1
    C. Valor mínimo. Ao configurar a propriedade platformFaultDomainCount, escolher o valor mínimo maximiza a resiliência das VMs em um conjunto de disponibilidade. Isso minimiza a quantidade de VMs impactadas em caso de falha de malha ou manutenção. Segundo o Copilot: C. Valor mínimo. Ao configurar a propriedade platformFaultDomainCount, escolher o valor mínimo maximiza a resiliência das VMs em um conjunto de disponibilidade. Isso minimiza a quantidade de VMs impactadas em caso de falha de malha ou manutenção.
  15. Miguel Angel 👍 1 Answered D
    La propiedad platformFaultDomainCount define cuántos Fault Domains tendrá el Availability Set. Los Fault Domains representan grupos de hardware con alimentación eléctrica y red compartidas. Si se produce un fallo físico en un rack o en su infraestructura asociada, solo se verá afectado un Fault Domain. Cuantos más Fault Domains utilices, mayor será la distribución de las máquinas virtuales y mayor la disponibilidad frente a fallos de hardware
  16. LaReis 👍 1
    Segundo o Copilot: C. Valor mínimo. Ao configurar a propriedade platformFaultDomainCount, escolher o valor mínimo maximiza a resiliência das VMs em um conjunto de disponibilidade. Isso minimiza a quantidade de VMs impactadas em caso de falha de malha ou manutenção.
  17. thalasi 👍 1 Answered D
    In an ARM template, an availability set has two key properties: platformFaultDomainCount platformUpdateDomainCount Uses the full number of available fault domains, achieving the highest availability. Most regions support 2, some support 3.
  18. othiagopadua 👍 1 Answered D
    O Azure espalha suas VMs automaticamente entre os domínios disponíveis. O objetivo é usar o valor máximo possível de domínios de falha, para garantir alta disponibilidade, dessa forma ganhamos operabilidade, a D é a melhor opçao
  19. Madbo 👍 1
    I selected option D - Max Value - as the value to configure for the platformFaultDomainCount property in the ARM template to allow for the maximum number of VMs to remain accessible in the event of fabric failure or maintenance.
  20. james2033 👍 1 Answered D
    Key word “as many VMs as possible” , it is max value (3) . See https://learn.microsoft.com/en-us/azure/virtual-machine-scale-sets/virtual-machine-scale-sets-manage-fault-domains#rest-api
  21. NaoVaz 👍 1 Answered D
    The Max Failed Domains is 3 inside a availability Set. Seeing that this option is not available, I believe the correct option is D) "Max Value".
  22. GBAU 👍 1
    Given the 10 and 20 are not valid answers as the max is 5 then we are only left with Min Value or Max Value. Logic dictates it is Max Value :)
  23. Arch9 👍 1 Answered D
    Default value for default domain is one. You need set default domain count for max availability.
  24. Saurabh_Bhargav 👍 1
    D is correct , Max fault domain is 3 so that option is not available so i will go with max
  25. SushilJinder 👍 1
    this implies that they are asking for max value .."as many VMs as possible......"

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