- A
Virtual Machine Scale Sets configured with autoscale rules based on CPU and distributed across availability zones
VM Scale Sets allow you to define autoscale conditions (e.g., scale out when CPU > 75%) and can be deployed across availability zones. This provides both horizontal scaling and protection against a zone failure.
- B
Azure App Service with autoscale rules and deployment slots
Why wrong: Azure App Service is a platform-as-a-service (PaaS) offering, not based on VMs. The requirement specifies Azure VMs, so App Service is not appropriate.
- C
Azure Load Balancer with a backend pool of VMs and autoscale rules applied to individual VMSS
Why wrong: While Load Balancer distributes traffic, it does not provide autoscaling itself. You would still need VMSS for auto-scaling. This option is incomplete because it separates the autoscale from the compute platform.
- D
Azure Traffic Manager with endpoints in separate regions and Manual scaling of VMs
Why wrong: Traffic Manager is for global traffic routing, not intra-region auto-scaling. Manual scaling does not meet the requirement for automatic scaling based on CPU. Also, it does not address zone-level high availability within a region.
Quick Answer
The answer is Virtual Machine Scale Sets configured with autoscale rules based on CPU and distributed across availability zones. This combination directly addresses the need for VMSS autoscale high availability across zones by automatically adding or removing VM instances in response to CPU utilization spikes, while distributing those instances across physically separate datacenters within a region to survive a full zone failure. On the Microsoft Azure Solutions Architect Expert AZ-305 exam, this scenario tests your understanding of combining horizontal scaling with fault isolation—a common trap is choosing a single-region deployment or relying on an availability set, which protects against rack failures but not entire datacenter outages. Remember that availability zones provide datacenter-level redundancy, whereas availability sets only protect against hardware failures within one datacenter. A useful memory tip: think “zones for zombies”—if a whole datacenter dies, only zones keep your app alive.
AZ-305 Design infrastructure solutions Practice Question
This AZ-305 practice question tests your understanding of design infrastructure solutions. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 wants to deploy a web application on Azure virtual machines (VMs). The application experiences variable traffic patterns, so the company needs to automatically add or remove VM instances based on CPU utilization. They also want the application to remain highly available even if an Azure datacenter fails. Which combination of Azure services should they use?
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
Virtual Machine Scale Sets configured with autoscale rules based on CPU and distributed across availability zones
Virtual Machine Scale Sets (VMSS) with autoscale rules based on CPU utilization automatically add or remove VM instances to match variable traffic patterns. Distributing the VMSS across availability zones ensures the application remains highly available even if an entire Azure datacenter fails, because availability zones are physically separate datacenters within a region.
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.
- ✓
Virtual Machine Scale Sets configured with autoscale rules based on CPU and distributed across availability zones
Why this is correct
VM Scale Sets allow you to define autoscale conditions (e.g., scale out when CPU > 75%) and can be deployed across availability zones. This provides both horizontal scaling and protection against a zone failure.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Azure App Service with autoscale rules and deployment slots
Why it's wrong here
Azure App Service is a platform-as-a-service (PaaS) offering, not based on VMs. The requirement specifies Azure VMs, so App Service is not appropriate.
- ✗
Azure Load Balancer with a backend pool of VMs and autoscale rules applied to individual VMSS
Why it's wrong here
While Load Balancer distributes traffic, it does not provide autoscaling itself. You would still need VMSS for auto-scaling. This option is incomplete because it separates the autoscale from the compute platform.
- ✗
Azure Traffic Manager with endpoints in separate regions and Manual scaling of VMs
Why it's wrong here
Traffic Manager is for global traffic routing, not intra-region auto-scaling. Manual scaling does not meet the requirement for automatic scaling based on CPU. Also, it does not address zone-level high availability within a region.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse Azure App Service (PaaS) with IaaS VM solutions, or assume that a load balancer alone can handle autoscaling, when in fact autoscale rules must be configured directly on the VMSS resource.
Detailed technical explanation
How to think about this question
VMSS autoscale uses Azure Monitor metrics (e.g., Percentage CPU) and triggers scale-out or scale-in operations based on configured thresholds and cool-down periods. Availability zones provide a 99.99% SLA for VMSS when two or more zones are used, as each zone is an isolated fault domain with independent power, cooling, and networking. Under the hood, the scale set orchestrator uses a virtual machine scale set model to maintain the desired instance count, and the autoscale engine evaluates metrics every 1-5 minutes to decide scaling actions.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this AZ-305 question test?
Design infrastructure solutions — This question tests Design infrastructure solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Virtual Machine Scale Sets configured with autoscale rules based on CPU and distributed across availability zones — Virtual Machine Scale Sets (VMSS) with autoscale rules based on CPU utilization automatically add or remove VM instances to match variable traffic patterns. Distributing the VMSS across availability zones ensures the application remains highly available even if an entire Azure datacenter fails, because availability zones are physically separate datacenters within a region.
What should I do if I get this AZ-305 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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