The answer is that the policy condition requires a managed disk, but the VMs might have unmanaged disks. This is because the `auditIfNotExists` effect relies on a `field` condition checking for `Microsoft.Compute/virtualMachines/storageProfile.osDisk.managedDisk.id`, which only exists when a VM uses a managed disk. If the VM uses an unmanaged disk, that property is absent, causing the condition to evaluate as false and preventing the existence check for the Azure Security extension from ever running. On the Microsoft Cybersecurity Architect exam, this tests your understanding of how policy conditions interact with resource properties—a common trap is assuming `auditIfNotExists` will always evaluate the existence condition, when in fact the parent condition must first be true. A useful memory tip is "no managed disk, no audit trigger"—the condition gate must pass before the extension check begins.
SC-100 Practice Question: Design solutions that align with security best practices and priorities
This SC-100 practice question tests your understanding of design solutions that align with security best practices and priorities. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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.
Refer to the exhibit. You are an Azure security engineer reviewing a custom Azure Policy definition. The policy is intended to audit virtual machines to ensure they have the Azure Security extension installed. However, the policy is not triggering on any resources. What is the most likely reason?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The policy condition requires a managed disk, but the VMs might have unmanaged disks.
Option A is correct because the policy condition uses `field` to check for `Microsoft.Compute/virtualMachines/storageProfile.osDisk.managedDisk.id`, which requires the VM to have a managed disk. If the VMs use unmanaged disks (i.e., the `managedDisk` property is absent), the condition evaluates to false, and the `auditIfNotExists` effect never triggers the existence check for the Azure Security extension.
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.
✓
The policy condition requires a managed disk, but the VMs might have unmanaged disks.
Why this is correct
If the VM does not have a managed disk, the 'if' condition is false, and the policy does not evaluate the audit effect.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The 'existenceCondition' field path is incorrect; it should be 'Microsoft.Compute/virtualMachines/extensions/publisher'.
Why it's wrong here
The field path is relative to the extension resource, so 'publisher' is correct.
✗
The policy is assigned to a management group, but the VMs are in a subscription under a different management group.
Why it's wrong here
Policy assignments are inherited; if assigned to a management group, it applies to all child subscriptions.
✗
The policy effect should be 'Deny' instead of 'auditIfNotExists'.
Why it's wrong here
The effect is correct for auditing; deny would block creation.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates focus on the `existenceCondition` or effect syntax, overlooking that the parent `field` condition silently fails on VMs without managed disks, preventing the entire policy from evaluating.
Detailed technical explanation
How to think about this question
Azure Policy's `field` condition evaluates the resource's ARM JSON representation. For VMs with unmanaged disks, the `managedDisk` property is entirely absent from the `storageProfile.osDisk` object, causing the `field` operator to return `null` and the condition to fail. This is a common pitfall when writing policies that assume all VMs use managed disks, especially in hybrid or legacy environments. The `auditIfNotExists` effect only proceeds to check for the extension if the parent condition (the `field` check) is true.
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
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this SC-100 question in full detail.
Design solutions that align with security best practices and priorities — This question tests Design solutions that align with security best practices and priorities — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The policy condition requires a managed disk, but the VMs might have unmanaged disks. — Option A is correct because the policy condition uses `field` to check for `Microsoft.Compute/virtualMachines/storageProfile.osDisk.managedDisk.id`, which requires the VM to have a managed disk. If the VMs use unmanaged disks (i.e., the `managedDisk` property is absent), the condition evaluates to false, and the `auditIfNotExists` effect never triggers the existence check for the Azure Security extension.
What should I do if I get this SC-100 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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