AZ-900 Describe Azure architecture and services Practice Question
A company is deploying a critical application on Azure Virtual Machines. They need to ensure that the application remains available during Azure platform updates. They also want to distribute the VMs across fault domains within an availability set. What is the primary purpose of fault domains?
⚠ Common exam trap
It's easy for candidates to confuse fault domains with availability zones, but fault domains are a rack-level isolation mechanism within a single datacenter, while availability zones span multiple datacenters within a region.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
To distribute VMs across different power and cooling racks
Fault domains represent groupings of hardware that share a common power source and network switch. By distributing VMs across multiple fault domains within an availability set, Azure ensures that if a power or cooling failure occurs in one rack, only the VMs in that fault domain are affected, keeping the application available on VMs in other fault domains.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
To distribute VMs across different power and cooling racks
Why this is correct
Fault domains group VMs that share the same power source, network switch, and cooling infrastructure within an Azure datacenter. By distributing VM instances across multiple fault domains, you isolate them from a single rack-level hardware failure, ensuring a power or cooling outage in one rack does not compromise the entire application's availability.
- ✗
To distribute VMs across different Azure regions
Why it's wrong here
Azure regions are broad geographical areas containing multiple datacenters, and fault domains do not span across regions—they are confined to a single datacenter. Fault domains protect against hardware failures local to a rack or datacenter, whereas cross-region resilience is achieved through paired regions or availability zones for disaster recovery. Spreading VMs across Azure regions would be an entirely different redundancy strategy.
When this WOULD be correct
This option would be correct if the question asked: 'What is the primary purpose of Azure paired regions?' or 'How can you ensure disaster recovery by distributing VMs across geographically separate locations?'
- ✗
To distribute VMs across different availability zones
Why it's wrong here
Availability zones are physically separate datacenters within an Azure region, each with independent power, cooling, and network connectivity. Fault domains, in contrast, are a finer-grained subdivision inside a single datacenter, isolating against rack-level failures rather than entire datacenter outages. Deploying across availability zones addresses a larger-scale disaster scenario, but it is not the purpose of configuring multiple fault domains.
When this WOULD be correct
A question asking how to protect VMs from a complete datacenter failure within a region, where the requirement is to place VMs in physically separate locations with independent infrastructure. In that case, distributing across availability zones would be correct.
- ✗
To distribute VMs across different virtual networks
Why it's wrong here
Virtual networks (VNets) are logical constructs for network isolation, IP addressing, and traffic segmentation, not physical hardware boundaries. Spreading VMs across different VNets does not affect their placement on physical racks, so it cannot provide protection from power or cooling failures that fault domains address. Even VMs in different VNets may reside on the same physical rack.
When this WOULD be correct
A question asking about distributing VMs across different subnets or network segments to improve network isolation or security would make this correct. For example: 'A company needs to separate development and production VMs on Azure. What should they use?'
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The AZ-900 exam frequently reuses these exact scenarios with slightly different constraints.
✓To distribute VMs across different power and cooling racksCorrect answer▾
Why this is correct
Fault domains group VMs that share the same power source, network switch, and cooling infrastructure within an Azure datacenter. By distributing VM instances across multiple fault domains, you isolate them from a single rack-level hardware failure, ensuring a power or cooling outage in one rack does not compromise the entire application's availability.
✗To distribute VMs across different Azure regionsWrong answer — click to see why▾
Why this is wrong here
Fault domains are a feature of availability sets within a single Azure region, not across regions. Distributing VMs across regions is achieved by using Azure Site Recovery or paired regions, not fault domains.
★ When this WOULD be the correct answer
This option would be correct if the question asked: 'What is the primary purpose of Azure paired regions?' or 'How can you ensure disaster recovery by distributing VMs across geographically separate locations?'
Why candidates choose this
Candidates may confuse fault domains with high-level disaster recovery concepts, thinking that distributing across regions provides similar fault tolerance, but fault domains operate within a single datacenter.
✗To distribute VMs across different availability zonesWrong answer — click to see why▾
Why this is wrong here
Fault domains distribute VMs across different power and cooling racks within a single Azure region, not across availability zones. Availability zones are separate physical locations within a region, each with independent power, cooling, and networking.
★ When this WOULD be the correct answer
A question asking how to protect VMs from a complete datacenter failure within a region, where the requirement is to place VMs in physically separate locations with independent infrastructure. In that case, distributing across availability zones would be correct.
Why candidates choose this
Candidates confuse fault domains with availability zones because both involve physical separation for high availability, but fault domains operate within a single datacenter rack, while availability zones span multiple datacenters.
✗To distribute VMs across different virtual networksWrong answer — click to see why▾
Why this is wrong here
Fault domains distribute VMs across different power and cooling racks within a single Azure region, not across virtual networks. Virtual networks are logical isolation boundaries for network traffic, not physical infrastructure fault boundaries.
★ When this WOULD be the correct answer
A question asking about distributing VMs across different subnets or network segments to improve network isolation or security would make this correct. For example: 'A company needs to separate development and production VMs on Azure. What should they use?'
Why candidates choose this
Candidates may confuse fault domains with network-level isolation, thinking that distributing VMs across virtual networks provides similar fault tolerance, but fault domains address physical hardware failures, not network segmentation.
Analysis generated from the official AZ-900blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Go deeper
Related to this question
Learn chapter
Azure Regions and Geographies
Key term
Availability
Availability is the measure of how often a system or service is operational and accessible when needed, typically expressed as a percentage of uptime.
Key term
Fault domain
A fault domain is a boundary within a computing environment that groups together components that share a single point of failure, helping to isolate the impact of hardware or software failures.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This AZ-900 practice question is part of Courseiva's free Microsoft certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the AZ-900 exam.