The answer is that the App Service 'myapp' does not have a managed identity enabled, which causes the principalId to be null in the ARM template role assignment. This occurs because the template likely uses the reference function to retrieve the App Service’s identity.principalId after deployment, but if the managed identity was never configured on the resource, that property remains null, breaking the role assignment. On the Microsoft Azure Developer Associate AZ-204 exam, this tests your understanding of how ARM template dependencies and the reference function interact with resource properties—specifically that a role assignment’s principalId must be a valid, non-null GUID from an enabled identity. A common trap is assuming the reference function will automatically create the identity, but it only reads existing properties. Remember the mnemonic: “No identity, no principalId—assign the role after you enable the ID.”
AZ-204 Implement Azure security Practice Question
This AZ-204 practice question tests your understanding of implement azure security. 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.
Exhibit
Refer to the exhibit.
{
"type": "Microsoft.Authorization/roleAssignments",
"apiVersion": "2022-04-01",
"name": "[guid(resourceGroup().id, 'Storage Blob Data Contributor')]",
"properties": {
"roleDefinitionId": "[subscriptionResourceId('Microsoft.Authorization/roleDefinitions', 'ba92f5b4-2d11-453d-a403-e96b0029c9fe')]",
"principalId": "[reference(resourceId('Microsoft.Web/sites', 'myapp'), '2022-03-01', 'Full').identity.principalId]",
"scope": "[resourceId('Microsoft.Storage/storageAccounts', 'mystorageacct')]"
}
}
Refer to the exhibit. You are deploying an ARM template that assigns the 'Storage Blob Data Contributor' role to the managed identity of an App Service named 'myapp' at the storage account 'mystorageacct' scope. The deployment fails with an error that 'principalId' is null. What is the most likely cause?
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 App Service 'myapp' does not have a managed identity enabled.
The reference function retrieves the App Service resource after it has been created, but if the App Service does not have a managed identity enabled, the 'identity.principalId' will be null. The template likely did not enable the managed identity on the App Service. Option B is correct. Option A is wrong because the role definition ID is correct. Option C is wrong because the scope is correct. Option D is wrong because the name is unique.
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 role definition ID is incorrect.
Why it's wrong here
The GUID 'ba92f5b4-2d11-453d-a403-e96b0029c9fe' is correct for Storage Blob Data Contributor.
✗
The storage account name 'mystorageacct' does not exist.
Why it's wrong here
A missing storage account would cause a different error.
✗
The role assignment name is not unique.
Why it's wrong here
The guid function generates a unique name.
✓
The App Service 'myapp' does not have a managed identity enabled.
Why this is correct
Without managed identity, principalId is null.
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 AZ-204 question in full detail.
Identify which AZ-204 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Implement Azure security — This question tests Implement Azure security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The App Service 'myapp' does not have a managed identity enabled. — The reference function retrieves the App Service resource after it has been created, but if the App Service does not have a managed identity enabled, the 'identity.principalId' will be null. The template likely did not enable the managed identity on the App Service. Option B is correct. Option A is wrong because the role definition ID is correct. Option C is wrong because the scope is correct. Option D is wrong because the name is unique.
What should I do if I get this AZ-204 question wrong?
Identify which AZ-204 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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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