Question 994 of 1,031

Describe Azure architecture and services →mediumMultiple ChoiceObjective-mapped

Quick Answer

The answer is to create an Availability Set containing two VMs per tier, configured with two fault domains and five update domains. This configuration directly addresses the need for high availability by separating VMs into distinct fault domains, which isolate them from unplanned hardware failures like rack or power outages, and into update domains, which stagger planned maintenance events such as OS patching so that only one domain is rebooted at a time. On the AZ-900 exam, this scenario tests your understanding of how Availability Sets provide resilience within a single Azure region, contrasting with Availability Zones which require multiple physical locations. A common trap is confusing update domains with fault domains—remember that fault domains protect against hardware failure (think "fault" = physical breakage), while update domains protect against software maintenance (think "update" = planned reboot). A helpful memory tip: two fault domains keep your VMs on separate hardware, while five update domains ensure only 20% of VMs are down during updates, guaranteeing at least one VM per tier stays running.

AZ-900 Describe Azure architecture and services Practice Question

This AZ-900 practice question tests your understanding of describe azure architecture and services. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

A company plans to deploy a three-tier web application in Azure. The application consists of web servers, application servers, and database servers. The company wants to protect the virtual machines (VMs) from planned maintenance events (e.g., OS updates) and unplanned hardware failures. They want to ensure that at least one VM in each tier remains available during such events. The solution should be deployed entirely within a single Azure region. What should the company use for the VMs?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "least"
Why it matters: You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.

Question 1mediummultiple choice

Full question →

A
Deploy the VMs across three Availability Zones (Zone 1, Zone 2, and Zone 3) within the region.
Why wrong: Availability Zones provide resilience by placing VMs in separate physical datacenters within a region. However, the requirement is for protection within a single region without specifying multi-datacenter redundancy. Availability Zones incur higher cost and are overkill when the goal is simply to protect against failures within one datacenter. Moreover, Availability Zones are not available in all regions, and they require each VM to be in a different zone to protect against zonal failures, which is more than what is needed.
B
Create an Availability Set containing two VMs per tier, configured with two fault domains and five update domains.
This is correct. An Availability Set protects VMs from failures within a single Azure datacenter by isolating them across fault domains (separate power and network) and update domains (sequential maintenance). Two fault domains ensure that not all VMs are affected by a single hardware failure. Five update domains ensure that only 20% of VMs are taken offline during planned maintenance. With two VMs per tier, at least one VM in each tier remains available during an event.
C
Configure a single Virtual Machine Scale Set that includes all the VMs for all three tiers.
Why wrong: A Virtual Machine Scale Set is designed to deploy and manage a set of identical, load-balanced VMs (e.g., for stateless web servers). It does not natively handle different application tiers (web, app, database) as a single set because each tier requires separate configurations, network security rules, and scaling policies. Additionally, a scale set does not inherently provide the fault and update domain isolation that an availability set offers for ensuring at least one VM per tier survives failures.
D
Use a Virtual Machine Scale Set with autoscale configured to always keep a minimum number of VMs running.
Why wrong: Autoscaling adjusts the number of VM instances based on demand, but it does not protect against hardware failures or planned maintenance. If a VM hosting a critical application component fails, autoscale may eventually replace it, but during the failure, availability is compromised. Furthermore, autoscaling does not guarantee that at least one VM in each specific tier remains available simultaneously, as it treats all VMs as identical.

Full breakdown with real-world context →

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

✓

Create an Availability Set containing two VMs per tier, configured with two fault domains and five update domains.

Option B is correct because an Availability Set with two fault domains and five update domains ensures that VMs are distributed across separate physical hardware (fault domains) and that planned maintenance (update domains) is staggered, so at least one VM per tier remains available during both planned and unplanned events. This meets the requirement of high availability within a single Azure region without needing multiple zones.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
Deploy the VMs across three Availability Zones (Zone 1, Zone 2, and Zone 3) within the region.
Why it's wrong here
Availability Zones provide resilience by placing VMs in separate physical datacenters within a region. However, the requirement is for protection within a single region without specifying multi-datacenter redundancy. Availability Zones incur higher cost and are overkill when the goal is simply to protect against failures within one datacenter. Moreover, Availability Zones are not available in all regions, and they require each VM to be in a different zone to protect against zonal failures, which is more than what is needed.
✓
Create an Availability Set containing two VMs per tier, configured with two fault domains and five update domains.
Why this is correct
This is correct. An Availability Set protects VMs from failures within a single Azure datacenter by isolating them across fault domains (separate power and network) and update domains (sequential maintenance). Two fault domains ensure that not all VMs are affected by a single hardware failure. Five update domains ensure that only 20% of VMs are taken offline during planned maintenance. With two VMs per tier, at least one VM in each tier remains available during an event.
Clue confirmation
The clue word "least" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Configure a single Virtual Machine Scale Set that includes all the VMs for all three tiers.
Why it's wrong here
A Virtual Machine Scale Set is designed to deploy and manage a set of identical, load-balanced VMs (e.g., for stateless web servers). It does not natively handle different application tiers (web, app, database) as a single set because each tier requires separate configurations, network security rules, and scaling policies. Additionally, a scale set does not inherently provide the fault and update domain isolation that an availability set offers for ensuring at least one VM per tier survives failures.
✗
Use a Virtual Machine Scale Set with autoscale configured to always keep a minimum number of VMs running.
Why it's wrong here
Autoscaling adjusts the number of VM instances based on demand, but it does not protect against hardware failures or planned maintenance. If a VM hosting a critical application component fails, autoscale may eventually replace it, but during the failure, availability is compromised. Furthermore, autoscaling does not guarantee that at least one VM in each specific tier remains available simultaneously, as it treats all VMs as identical.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates often confuse Availability Zones (which protect against datacenter-level failures) with Availability Sets (which protect against rack-level failures within a single datacenter), and fail to recognize that the question explicitly limits the solution to a single Azure region, making Availability Sets the appropriate choice for the described planned and unplanned events.

Detailed technical explanation

How to think about this question

An Availability Set uses fault domains (up to 3) to isolate VMs from shared hardware failures like rack or power supply issues, and update domains (up to 20) to sequence planned maintenance so only one domain is updated at a time. With two fault domains and five update domains, each tier's VMs are placed in separate fault domains (e.g., VM1 in FD0, VM2 in FD1) and staggered across update domains, ensuring that even if one fault domain fails or an update domain is rebooted, the other VM in the same tier remains operational.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.

TExam Day Tips

Watch for words such as best, first, most likely and least administrative effort.
Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this AZ-900 question test?

Describe Azure architecture and services — This question tests Describe Azure architecture and services — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: Create an Availability Set containing two VMs per tier, configured with two fault domains and five update domains. — Option B is correct because an Availability Set with two fault domains and five update domains ensures that VMs are distributed across separate physical hardware (fault domains) and that planned maintenance (update domains) is staggered, so at least one VM per tier remains available during both planned and unplanned events. This meets the requirement of high availability within a single Azure region without needing multiple zones.

What should I do if I get this AZ-900 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

Are there clue words in this question I should notice?

Yes — watch for: "least". You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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Same concept, more angles

1 more ways this is tested on AZ-900

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. A company deploys two Azure virtual machines in an availability set. The application requires that at least one VM remains running during Azure platform-initiated maintenance, such as operating system updates to the underlying host. Which component of the availability set directly ensures that the VMs are not updated at the same time?

medium

A.Fault domains
✓ B.Update domains
C.Proximity placement groups
D.Availability zones

Why B: Update domains (B) are the correct component because they logically group VMs that are updated together during Azure platform-initiated maintenance. By placing VMs in different update domains, Azure ensures that only one update domain is taken offline at a time, guaranteeing that at least one VM remains running during host OS updates.

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