The answer is Option D, using Azure Functions with a Service Bus queue trigger and duplicate detection. This approach is correct because it decouples the upload from processing, minimizing user latency by immediately returning control to the client, while Service Bus’s built-in duplicate detection ensures idempotent processing by automatically discarding duplicate messages within a defined time window, preventing duplicate thumbnails. On the AZ-204 exam, this scenario tests your understanding of serverless asynchronous patterns and the distinction between trigger types—a common trap is choosing Blob Storage triggers (Option A), which can cause duplicate processing on blob re-writes and lack native deduplication. Remember the memory tip: “Queue for decoupling, dedup for idempotency”—Service Bus queues with duplicate detection are purpose-built for exactly this resilient, serverless image upload processing workflow.
AZ-204 Develop Azure compute solutions Practice Question
This AZ-204 practice question tests your understanding of develop azure compute solutions. 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 developing a web application that allows users to upload images. The application is deployed on Azure App Service. After upload, the images must be processed to generate thumbnails and to extract metadata. The processing should happen asynchronously and must be resilient to failures. You need to design the solution using serverless components. The solution must minimize latency for the user during upload, and the processing must be retried automatically if it fails. You also need to ensure that the processing is idempotent, so that duplicate messages do not cause duplicate thumbnails. Which approach should you use?
Option A: Use Azure Functions with a Blob Storage trigger to process each image as it is uploaded. The function generates thumbnails and stores metadata in Cosmos DB. Use the `leaseBlob` property to prevent duplicate processing.
Option B: Use Azure Functions with an Event Grid trigger to process images. The function generates thumbnails and stores metadata in Cosmos DB. Use Event Grid's built-in retry policy and idempotent logic in the function.
Option C: Use Azure Logic Apps with a Blob Storage connector to process images. The logic app generates thumbnails and stores metadata in Cosmos DB. Configure retry policy on the connector.
Option D: Use Azure Functions with a Service Bus queue trigger. The web app sends a message to the queue after upload. The function processes the message, generates thumbnails, and stores metadata. Use message deduplication to ensure idempotency.
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "minimum / minimize"
Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Azure Functions with Service Bus queue trigger and duplicate detection
Option D is correct because it uses a Service Bus queue with duplicate detection, which ensures idempotent processing by automatically discarding duplicate messages within a defined time window. The web app uploads the image and immediately sends a message to the queue, minimizing user latency. The Azure Function triggered by the queue processes the image asynchronously, and Service Bus's built-in retry policy (via dead-lettering and max delivery count) provides resilience against failures.
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.
✗
Azure Functions with Blob Storage trigger, using leaseBlob
Why it's wrong here
Blob trigger processes each blob once, but if the function fails and retries, it could reprocess; no built-in deduplication.
✗
Azure Logic Apps with Blob Storage connector
Why it's wrong here
Logic Apps can handle retries but are more complex and costly for simple processing.
✗
Azure Functions with Event Grid trigger
Why it's wrong here
Event Grid does not guarantee deduplication; duplicate events may occur.
✓
Azure Functions with Service Bus queue trigger and duplicate detection
Why this is correct
Service Bus duplicate detection ensures idempotency; the queue separates upload from processing.
Clue confirmation
The clue word "minimum / minimize" 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
The trap here is that candidates often choose Event Grid (Option B) because it is serverless and has retry policies, but they overlook that Event Grid does not provide built-in message deduplication, which is critical for idempotent processing in this scenario.
Detailed technical explanation
How to think about this question
Service Bus queue duplicate detection uses the `MessageId` property to identify duplicates within a time window (default 30 seconds, configurable up to 7 days). When the web app sends a message with a unique `MessageId` (e.g., based on the blob name or a GUID), Service Bus automatically discards any subsequent message with the same `MessageId` within the window. This ensures that even if the web app sends the message multiple times (e.g., due to retries), the function processes it only once, achieving idempotency without custom logic.
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 AZ-204 question in full detail.
Develop Azure compute solutions — This question tests Develop Azure compute solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Azure Functions with Service Bus queue trigger and duplicate detection — Option D is correct because it uses a Service Bus queue with duplicate detection, which ensures idempotent processing by automatically discarding duplicate messages within a defined time window. The web app uploads the image and immediately sends a message to the queue, minimizing user latency. The Azure Function triggered by the queue processes the image asynchronously, and Service Bus's built-in retry policy (via dead-lettering and max delivery count) provides resilience against failures.
What should I do if I get this AZ-204 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: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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