AZ-104 Implement and Manage Virtual Networking Practice Question
You have an Azure load balancer in front of two virtual machines. The load balancer reports both instances as unavailable even though the VMs are running. What is the most likely cause?
⚠ Common exam trap
Many exam-takers assume 'VM is running' means it is automatically available to the load balancer, overlooking the critical role of the health probe configuration and the need for the probe traffic to be allowed by network security rules.
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
✓
The health probe is failing.
The health probe is the mechanism by which the Azure Load Balancer determines the availability of backend instances. If the probe is misconfigured (e.g., wrong port, protocol, path, or interval) or the backend VMs are not responding to the probe requests (e.g., firewall blocking the probe traffic or the application not listening on the specified port), the load balancer marks both instances as 'Unavailable' even though the VMs are running. This is the most common cause of backend pool unavailability.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The health probe is failing.
Why this is correct
The health probe is failing. Azure Load Balancer continuously sends HTTP, TCP, or HTTPS probes to the configured backend pool endpoints. If the probe does not receive the expected response within the timeout interval, the load balancer marks that backend instance as unhealthy and stops routing new traffic to it, directly causing the symptom of unavailable virtual machines.
- ✗
The VMs are in an availability set.
Why it's wrong here
The VMs are in an availability set. An availability set is a logical grouping that spreads VMs across fault domains and update domains to protect against hardware failures and maintenance events. It does not remove a VM from a load balancer's backend pool; in fact, load balancers frequently work with availability sets to provide high availability. Membership in an availability set alone cannot make the VMs unreachable to the load balancer.
When this WOULD be correct
In a question asking 'What is the purpose of placing VMs in an availability set?', the correct answer would be 'To protect against datacenter-level failures by distributing VMs across fault domains and update domains.'
- ✗
The storage account uses the Cool tier.
Why it's wrong here
The storage account uses the Cool tier. Azure Storage access tiers (Hot, Cool, Cold, and Archive) are performance and cost optimizations for blob data, completely independent from compute networking resources. A load balancer routes traffic based on health probes and backend pool membership, not on storage configuration, so the Cool tier has no mechanism to influence VM availability behind the load balancer.
When this WOULD be correct
In a question about why data retrieval costs are high for infrequently accessed data stored in Azure Blob Storage, the Cool tier would be the correct answer because it has lower storage costs but higher access costs compared to the Hot tier.
- ✗
The subscription has a budget alert.
Why it's wrong here
The subscription has a budget alert. Budget alerts are cost management notifications triggered when spending reaches a threshold, and they are purely informational. They do not deprovision resources, alter network configurations, or modify load balancer backend health. Since they have no effect on the control plane or data plane of Azure Load Balancer, a budget alert cannot be the cause of backend instances being marked as unavailable.
When this WOULD be correct
In a scenario where a subscription budget alert is configured to automatically disable resources (e.g., via an Azure Policy or automation runbook) when a cost threshold is exceeded, the load balancer might show VMs as unavailable if the VMs are stopped or deallocated as a result.
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.
✓The health probe is failing.Correct answer▾
Why this is correct
The health probe is failing. Azure Load Balancer continuously sends HTTP, TCP, or HTTPS probes to the configured backend pool endpoints. If the probe does not receive the expected response within the timeout interval, the load balancer marks that backend instance as unhealthy and stops routing new traffic to it, directly causing the symptom of unavailable virtual machines.
✗The VMs are in an availability set.Wrong answer — click to see why▾
Why this is wrong here
An availability set ensures high availability by distributing VMs across fault domains, but it does not affect load balancer health probe status. The load balancer reports instances unavailable due to health probe failures, not availability set membership.
★ When this WOULD be the correct answer
In a question asking 'What is the purpose of placing VMs in an availability set?', the correct answer would be 'To protect against datacenter-level failures by distributing VMs across fault domains and update domains.'
Why candidates choose this
Candidates may confuse availability sets with load balancing health, thinking that being in an availability set automatically makes VMs healthy, or they may overthink the role of availability sets in load balancer configuration.
✗The storage account uses the Cool tier.Wrong answer — click to see why▾
Why this is wrong here
The storage account tier (Cool vs. Hot) affects access cost and latency for blob storage, not the health of VMs behind a load balancer. The load balancer's health probe failure is unrelated to storage account configuration.
★ When this WOULD be the correct answer
In a question about why data retrieval costs are high for infrequently accessed data stored in Azure Blob Storage, the Cool tier would be the correct answer because it has lower storage costs but higher access costs compared to the Hot tier.
Why candidates choose this
Candidates might confuse storage tier issues with general Azure resource health, or incorrectly assume that a misconfigured storage account could impact VM availability through dependencies like boot diagnostics or custom script extensions.
✗The subscription has a budget alert.Wrong answer — click to see why▾
Why this is wrong here
A budget alert does not affect load balancer health probe status; it only triggers cost-related notifications. The load balancer reports VMs as unavailable due to health probe failures, not subscription billing settings.
★ When this WOULD be the correct answer
In a scenario where a subscription budget alert is configured to automatically disable resources (e.g., via an Azure Policy or automation runbook) when a cost threshold is exceeded, the load balancer might show VMs as unavailable if the VMs are stopped or deallocated as a result.
Why candidates choose this
Candidates may confuse budget alerts with operational alerts that affect resource availability, or mistakenly think that budget constraints can directly impact load balancer health monitoring.
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?”
Go deeper
Related to this question
Learn chapter
Managed Identities for Azure Resources
Key term
Azure Load Balancer
Azure Load Balancer is a cloud service that evenly distributes incoming network traffic across multiple virtual machines or resources to ensure reliability and high availability.
Key term
Load balancer
A load balancer is a device or software that distributes incoming network traffic across multiple servers so no single server gets overwhelmed.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.