The answer is a missing 'Resource instances' firewall exception for the managed identity. Even though the managed identity has the correct 'Storage Blob Data Contributor' RBAC role and the 'Allow Azure services on the trusted services list' setting is enabled, that trusted services list only permits platform-level services, not the specific managed identity's resource. To bypass the ADLS Gen2 firewall, you must explicitly add the Synapse workspace as a 'Resource instances' exception under the storage account's firewall settings; without this, the managed identity's request is blocked at the network layer, causing the 'Permission denied' error. On the DP-203 exam, this scenario tests your understanding that RBAC and network firewalls are separate security layers—a common trap is assuming the trusted services list covers all managed identities. Remember the mnemonic: "RBAC for data, Firewall for network—both must say yes."
DP-203 Develop data processing Practice Question
This DP-203 practice question tests your understanding of develop data processing. 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.
You are troubleshooting a Synapse Spark notebook that fails when reading Parquet files from Azure Data Lake Storage Gen2. The error message indicates 'Permission denied'. The notebook uses a managed identity (System-assigned) for authentication. The Data Lake Storage account has a firewall enabled with 'Allow Azure services on the trusted services list' turned on. The storage account's RBAC role assignments include 'Storage Blob Data Contributor' for the managed identity. What is the most likely cause of the failure?
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 storage account firewall does not have a 'Resource instances' exception for the managed identity
Option C is correct because when a storage account firewall is enabled with 'Allow Azure services on the trusted services list' turned on, it only allows trusted Azure platform services to access the storage account, but it does not automatically grant access to a specific managed identity. To allow a managed identity to bypass the firewall, you must add a 'Resource instances' exception for that managed identity's resource (e.g., the Synapse workspace). Without this explicit exception, the managed identity's request is blocked by the firewall, resulting in a 'Permission denied' error even though the RBAC role assignment is correct.
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.
✗
Parquet files require special permissions that are not granted by RBAC roles
Why it's wrong here
RBAC roles cover data operations for Parquet files.
✗
The managed identity has not been granted the 'Storage Blob Data Reader' role in addition to 'Storage Blob Data Contributor'
Why it's wrong here
'Storage Blob Data Contributor' includes read permissions, so this is not the issue.
✓
The storage account firewall does not have a 'Resource instances' exception for the managed identity
Why this is correct
Firewall rules require explicit addition of the managed identity as a resource instance to allow access when the firewall is enabled.
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 notebook is using an incorrect connection string with account key
Why it's wrong here
The notebook uses managed identity authentication, not account key.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume 'Allow Azure services on the trusted services list' automatically includes all Azure resources with managed identities, but it only covers specific Azure platform services, not custom managed identities from services like Synapse.
Detailed technical explanation
How to think about this question
Azure Data Lake Storage Gen2 uses Azure RBAC for control plane access and POSIX-like ACLs for data plane access, but firewall rules are evaluated before RBAC or ACLs. The 'Resource instances' exception allows you to grant access to specific Azure resources (like a Synapse workspace) by their resource ID, enabling the managed identity to bypass the firewall. Without this exception, the firewall blocks all requests from the managed identity, even if RBAC roles are correctly assigned, because the 'Allow Azure services' setting only covers Azure platform services (e.g., Azure Backup, Azure Logic Apps) and not user-assigned or system-assigned managed identities.
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 DP-203 question in full detail.
Develop data processing — This question tests Develop data processing — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The storage account firewall does not have a 'Resource instances' exception for the managed identity — Option C is correct because when a storage account firewall is enabled with 'Allow Azure services on the trusted services list' turned on, it only allows trusted Azure platform services to access the storage account, but it does not automatically grant access to a specific managed identity. To allow a managed identity to bypass the firewall, you must add a 'Resource instances' exception for that managed identity's resource (e.g., the Synapse workspace). Without this explicit exception, the managed identity's request is blocked by the firewall, resulting in a 'Permission denied' error even though the RBAC role assignment is correct.
What should I do if I get this DP-203 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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