AZ-900 Describe Azure architecture and services Practice Question
A company plans to deploy two Azure virtual machines that host a critical web application. Both VMs will be in the same Azure region and the same virtual network. The company’s requirements are: 1) During Azure platform-initiated maintenance (e.g., OS updates), at least one VM must remain running. 2) If a hardware failure occurs in the server rack that hosts one VM, the other VM must not be affected. 3) The solution must not incur additional costs beyond the VMs themselves. Which Azure feature should the company configure?
⚠ Common exam trap
Test-takers frequently confuse Availability Zones (which provide physical separation across data centers) with Availability Sets (which provide fault and update domain isolation within a single data center), leading them to choose Availability Zones despite the cost and networking constraints that make Availability Sets the correct answer for this scenario.
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
✓
Availability Set
An Availability Set distributes VMs across multiple fault domains (different server racks with independent power and networking) and update domains (groups that undergo platform maintenance sequentially). This ensures that during Azure-initiated maintenance, only one update domain is rebooted at a time, leaving at least one VM running, and that a hardware failure in one fault domain does not affect VMs in other fault domains. Availability Sets are free of charge beyond the cost of the VMs themselves, meeting all requirements.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Availability Zones
Why it's wrong here
Availability Zones provide redundancy across physically separate datacenters within a region. This would satisfy the maintenance and rack failure requirements, but it may introduce additional costs due to inter-zone data transfer fees, and the requirement states that the solution must not incur additional costs beyond the VMs themselves. Therefore, Availability Zones are not the best choice.
When this WOULD be correct
A company needs to ensure high availability for a critical application across different physical datacenters within a region to protect against a full datacenter outage, and the budget allows for the additional cost of zone-redundant resources.
- ✓
Availability Set
Why this is correct
An Availability Set groups VMs across multiple fault domains (separate server racks) and update domains (for planned maintenance). This ensures that at least one VM remains available during maintenance and that a single rack failure does not affect both VMs. No additional cost is incurred for using an Availability Set.
- ✗
Azure Site Recovery
Why it's wrong here
Azure Site Recovery (ASR) is a disaster recovery service used to replicate workloads to a secondary region for recovery during a regional outage. It is not designed for within-region high availability during maintenance or rack-level hardware failures, and it adds significant cost for replication and failover.
- ✗
Azure Load Balancer
Why it's wrong here
An Azure Load Balancer distributes incoming traffic across multiple VMs. While it can work with an Availability Set to provide high availability, by itself it does not protect against rack failures or platform maintenance events. It also does not guarantee that VMs are placed on separate fault or update domains.
When this WOULD be correct
A company deploys multiple VMs in the same availability set and needs to distribute incoming traffic evenly across them to improve application responsiveness and provide high availability by routing around failed VMs. The requirement is for load balancing, not fault isolation or maintenance handling.
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.
✓Availability SetCorrect answer▾
Why this is correct
An Availability Set groups VMs across multiple fault domains (separate server racks) and update domains (for planned maintenance). This ensures that at least one VM remains available during maintenance and that a single rack failure does not affect both VMs. No additional cost is incurred for using an Availability Set.
✗Availability ZonesWrong answer — click to see why▾
Why this is wrong here
Availability Zones protect against datacenter-level failures by distributing VMs across physically separate zones, but they incur additional costs for inter-zone traffic and do not guarantee that VMs remain in the same rack or fault domain for hardware failure isolation as required.
★ When this WOULD be the correct answer
A company needs to ensure high availability for a critical application across different physical datacenters within a region to protect against a full datacenter outage, and the budget allows for the additional cost of zone-redundant resources.
Why candidates choose this
Candidates may confuse Availability Zones with fault domains, thinking they provide the same rack-level isolation as an availability set, or they may overestimate the cost-effectiveness of zones without considering the specific requirement of no additional costs.
✗Azure Load BalancerWrong answer — click to see why▾
Why this is wrong here
Azure Load Balancer distributes traffic across VMs but does not provide fault isolation for hardware failures or guarantee VM availability during platform maintenance; it requires additional VMs to be useful and does not ensure at least one VM stays running during maintenance events.
★ When this WOULD be the correct answer
A company deploys multiple VMs in the same availability set and needs to distribute incoming traffic evenly across them to improve application responsiveness and provide high availability by routing around failed VMs. The requirement is for load balancing, not fault isolation or maintenance handling.
Why candidates choose this
Candidates may think a load balancer inherently provides high availability by distributing traffic, but they overlook that it does not protect against hardware failures affecting multiple VMs in the same rack or guarantee VM uptime during platform maintenance without additional features like availability sets.
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
Feature
A feature is a distinct unit of functionality that delivers value to the user, often managed and tracked throughout the software development lifecycle.
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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.