Question 377 of 1,049
AZ-104 Deploy and Manage Azure Compute Practice Question
You have a virtual machine scale set that must increase the number of instances automatically when average CPU utilization exceeds 75 percent and decrease when utilization drops below 30 percent. What should you configure?
⚠ Common exam trap
It's easy for candidates to confuse autoscale rules with other VM configuration options like boot diagnostics or custom script extensions, not realizing that autoscaling is a dedicated feature of Azure Monitor applied to scale sets.
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
✓
An Azure Monitor autoscale rule on the scale set
Azure Monitor autoscale rules allow you to define conditions for automatically scaling out (increasing instances) when average CPU utilization exceeds a threshold (e.g., 75%) and scaling in (decreasing instances) when it drops below a lower threshold (e.g., 30%). These rules are applied directly to the virtual machine scale set, enabling dynamic scaling based on performance metrics.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
An Azure Monitor autoscale rule on the scale set
Why this is correct
An Azure Monitor autoscale rule is the native scaling mechanism for Virtual Machine Scale Sets. It evaluates metric thresholds, such as average CPU percentage over a 10-minute window, and automatically adds or removes instances to match demand. Unlike static configuration or scripts, autoscale rules dynamically adjust capacity, making them the correct choice for increasing the scale set based on load.
- ✗
A boot diagnostics configuration
Why it's wrong here
Boot diagnostics is a troubleshooting feature that captures serial console logs and screenshots of a VM's startup process, storing them in a managed storage account. It provides visibility into boot failures but has no control over instance count or resource allocation. Therefore, it cannot scale out a scale set; it only helps diagnose issues after a scaling event or startup failure.
When this WOULD be correct
You need to troubleshoot a virtual machine that fails to boot and want to capture serial console output and screenshots to diagnose the issue. Configuring boot diagnostics on the VM would be the correct action.
- ✗
An availability set
Why it's wrong here
An availability set is a logical grouping of VMs that distributes instances across fault domains and update domains to protect against hardware failures and planned maintenance. It enhances resilience but does not monitor workload metrics or change the number of VM instances. Since Virtual Machine Scale Sets already provide similar fault-domain distribution, an availability set is irrelevant to increasing capacity based on demand.
When this WOULD be correct
You need to ensure that two or more VMs running a critical application are placed on different physical hardware to protect against a rack-level failure. Configuring an availability set would be the correct answer.
- ✗
A custom script extension
Why it's wrong here
The Custom Script Extension downloads and executes scripts on VM instances during provisioning, typically for configuring software or joining a domain. While it can prepare new instances for application traffic, it does not evaluate load metrics or make decisions about instance count. Autoscaling requires a policy-driven controller that can trigger scale-out, which the script extension is not designed to do.
When this WOULD be correct
You need to run a PowerShell script on each VM in a scale set after creation to install software or configure settings. A custom script extension would be the correct choice to automate that post-deployment configuration.
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-104 exam frequently reuses these exact scenarios with slightly different constraints.
✓An Azure Monitor autoscale rule on the scale setCorrect answer▾
Why this is correct
An Azure Monitor autoscale rule is the native scaling mechanism for Virtual Machine Scale Sets. It evaluates metric thresholds, such as average CPU percentage over a 10-minute window, and automatically adds or removes instances to match demand. Unlike static configuration or scripts, autoscale rules dynamically adjust capacity, making them the correct choice for increasing the scale set based on load.
✗A boot diagnostics configurationWrong answer — click to see why▾
Why this is wrong here
Boot diagnostics configuration captures serial logs and screenshots for VM troubleshooting, but it does not enable automatic scaling based on CPU utilization thresholds.
★ When this WOULD be the correct answer
You need to troubleshoot a virtual machine that fails to boot and want to capture serial console output and screenshots to diagnose the issue. Configuring boot diagnostics on the VM would be the correct action.
Why candidates choose this
Candidates may confuse boot diagnostics with performance monitoring or scaling, thinking it provides data that could trigger scaling actions, but it is purely for troubleshooting boot failures.
✗An availability setWrong answer — click to see why▾
Why this is wrong here
An availability set is used to distribute VMs across fault domains and update domains for high availability, not to automatically scale instances based on CPU utilization. It does not support autoscaling rules.
★ When this WOULD be the correct answer
You need to ensure that two or more VMs running a critical application are placed on different physical hardware to protect against a rack-level failure. Configuring an availability set would be the correct answer.
Why candidates choose this
Candidates may confuse availability sets with scale sets, thinking that availability sets also provide scaling capabilities, or they may associate 'availability' with the ability to handle load changes.
✗A custom script extensionWrong answer — click to see why▾
Why this is wrong here
A custom script extension is used to run scripts on VMs after deployment, not to configure autoscaling based on CPU utilization. It cannot define scaling rules or thresholds.
★ When this WOULD be the correct answer
You need to run a PowerShell script on each VM in a scale set after creation to install software or configure settings. A custom script extension would be the correct choice to automate that post-deployment configuration.
Why candidates choose this
Candidates may think a custom script extension can handle scaling logic because it can execute code, but it lacks the monitoring and rule-based triggering required for autoscaling.
Analysis generated from the official AZ-104blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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Last reviewed: Jun 11, 2026
This AZ-104 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-104 exam.
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