The correct choice is to use the Cosmos DB output binding with its built-in retry policy and configure the Event Hubs trigger to checkpoint only after successful writes. This design ensures at-least-once delivery because the built-in retry policy automatically handles transient failures when writing to Cosmos DB, while deferring the checkpoint prevents the Event Hubs partition offset from advancing until the data is durably stored. On the AZ-204 exam, this scenario tests your understanding of how Azure Functions integrates with Event Hubs and Cosmos DB to achieve resilience—specifically, the trap is to manually implement retry logic or checkpoint prematurely, which risks event loss. The key concept is that the output binding’s retry policy is a declarative, built-in mechanism that handles transient failures without custom code, and checkpointing only after success guarantees no events are missed. Memory tip: “Checkpoint after commit, retry with the binding” to remember that the binding handles retries, and checkpointing must follow a successful write.
AZ-204 Develop Azure compute solutions Practice Question
This AZ-204 practice question tests your understanding of develop azure compute solutions. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 designing a serverless application using Azure Functions that processes high-volume events from Azure Event Hubs. The events are then written to Azure Cosmos DB. The function must guarantee at-least-once delivery and be resilient to failures. The Cosmos DB account uses the SQL API and is configured with a single write region. You need to design the function to handle transient failures when writing to Cosmos DB without losing events. What should you do?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "least"
Why it matters: You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use the Cosmos DB output binding with built-in retry policy and configure the trigger to checkpoint only after successful writes.
Option D is correct because using the Cosmos DB output binding with its built-in retry policy automatically handles transient failures by retrying writes. By configuring the Event Hubs trigger to checkpoint only after a successful write, you ensure that events are not acknowledged until they are durably stored in Cosmos DB, guaranteeing at-least-once delivery and resilience to 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.
✗
Increase the Event Hubs trigger's batch size to reduce the number of writes.
Why it's wrong here
Batch size does not affect reliability.
✗
Implement a poison message queue to store failed events and reprocess them later.
Why it's wrong here
Poison queue discards messages after retries; events may be lost.
✗
In the function code, manually write to Cosmos DB and then manually checkpoint the Event Hubs partition.
Why it's wrong here
Manual checkpoint before write risks losing events if function crashes after checkpoint.
✓
Use the Cosmos DB output binding with built-in retry policy and configure the trigger to checkpoint only after successful writes.
Why this is correct
Output binding retries on failure; checkpoint after success ensures at-least-once.
Clue confirmation
The clue word "least" 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 think manual checkpointing gives them more control, but it actually introduces a window for data loss if the checkpoint occurs before the write is confirmed, whereas the output binding's built-in retry and automatic checkpointing on success provide a safer, more reliable pattern.
Detailed technical explanation
How to think about this question
The Cosmos DB output binding in Azure Functions uses the Azure Cosmos DB SDK's built-in retry logic, which by default retries on transient errors like 429 (rate limiting) and 503 (service unavailable) with exponential backoff. The Event Hubs trigger's checkpointing is tied to the function's success; if the output binding fails after all retries, the function throws an exception, preventing checkpoint advancement and ensuring the event is reprocessed. This pattern is critical for high-throughput scenarios where manual checkpointing could lead to lost events if the function crashes between a successful write and a checkpoint.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
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: Use the Cosmos DB output binding with built-in retry policy and configure the trigger to checkpoint only after successful writes. — Option D is correct because using the Cosmos DB output binding with its built-in retry policy automatically handles transient failures by retrying writes. By configuring the Event Hubs trigger to checkpoint only after a successful write, you ensure that events are not acknowledged until they are durably stored in Cosmos DB, guaranteeing at-least-once delivery and resilience to 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: "least". You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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