AZ-305 Design infrastructure solutions Practice Question
Your organization is deploying a critical application on Azure virtual machines. You need to ensure that the VMs are distributed across multiple fault domains and update domains within an availability set. You create an availability set with 3 fault domains and 5 update domains. How many VMs can you add to this availability set to maximize fault tolerance?
⚠ Common exam trap
The trap here is that candidates often multiply fault domains by update domains (3 × 5 = 15) and assume that is the maximum number of VMs, but Azure does not enforce such a product limit—the domains are logical groups, not slots that can hold only one VM each.
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
✓
Unlimited
B is correct because Azure availability sets do not limit the number of VMs you can place into them; you can add an unlimited number of VMs. The fault domains (3) and update domains (5) define the maximum distribution groups, but Azure will place VMs across these domains as evenly as possible. Adding more VMs beyond the number of fault or update domains does not reduce fault tolerance—it simply means multiple VMs will share the same fault or update domain, but the set still provides the best possible distribution given the defined domain counts.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
5 VMs
Why it's wrong here
Choosing 5 VMs as a maximum is incorrect because Azure availability sets allow you to add far more than five virtual machines. The update domain logic within an availability set distributes VMs across different maintenance and reboot groups, but it does not cap the total VM count at five; update domains simply ensure that during planned Azure maintenance, not all VMs are rebooted at once, so you can continue to scale out well beyond five instances.
- ✓
Unlimited
Why this is correct
The correct answer is that an availability set has no prescribed maximum number of VMs; instead, you can place as many VMs as your Azure subscription and regional capacity support. Availability sets are primarily a placement construct that separates VMs across fault and update domains to maximize availability, and they do not impose a numeric ceiling on the number of instances you can add. This means your critical application can scale to hundreds of VMs within a single availability set, constrained only by Azure quota limits and not by the availability set design.
- ✗
15 VMs
Why it's wrong here
Selecting 15 as the limit is erroneous because there is nothing in the availability set architecture that restricts you to fifteen virtual machines. The number 15 might be mistakenly derived from the fact that a default availability set often starts with three fault domains and five update domains, yielding 3×5=15 possible placement groups, but these are merely logical partitions, not an aggregate limit on VM count. You can place multiple VMs in the same fault and update domain combination, so the total number of VMs is limited by subscription quotas rather than by this 15-product calculation.
- ✗
3 VMs
Why it's wrong here
Limiting the availability set to 3 VMs is incorrect because there is no such bound based on fault domains. While an availability set typically uses three fault domains to isolate VMs from physical hardware failures, each fault domain can host many VMs simultaneously; the fault domain count is a placement topology, not a capacity constraint. Therefore, you can exceed three VMs by placing multiple instances within each of the three fault domains to achieve high availability.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This AZ-305 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-305 exam.