The answer is the Cosmos DB trigger. This is correct because the Azure Function Cosmos DB trigger natively integrates with the change feed, which captures insertions and updates in a container; the function runtime automatically polls this feed and invokes your code with batches of documents as they occur, providing a seamless serverless reaction to data changes. On the AZ-204 exam, this concept tests your understanding of event-driven architecture and the change feed pattern—a common trap is confusing the Cosmos DB trigger with the Event Grid trigger, but remember that the Cosmos DB trigger is purpose-built for reacting directly to container-level changes without needing an intermediary service. A helpful memory tip: think "Change Feed = Cosmos Trigger" to avoid mixing it up with other event sources.
AZ-204 Develop for Azure storage Practice Question
This AZ-204 practice question tests your understanding of develop for azure storage. 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 building a serverless application that needs to react to insertions and updates in an Azure Cosmos DB container. You want to process these changes using an Azure Function. Which trigger should you configure for the function?
The Cosmos DB trigger uses the change feed to respond to inserts and updates in the container.
B
Blob trigger
Why wrong: Blob trigger is for Azure Blob Storage, not Cosmos DB changes.
C
Event Grid trigger
Why wrong: Event Grid trigger can handle events from Cosmos DB but requires explicit event publishing; the Cosmos DB trigger is the native approach for change feed.
D
Service Bus trigger
Why wrong: Service Bus trigger processes messages from a queue or topic, not database changes.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Cosmos DB trigger
A Cosmos DB trigger is the correct choice because it is specifically designed to react to changes in a Cosmos DB container by leveraging the change feed. The Azure Function runtime polls the change feed for inserts and updates, invoking the function with batches of documents as they occur. This provides a native, serverless integration without needing additional services.
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.
✓
Cosmos DB trigger
Why this is correct
The Cosmos DB trigger uses the change feed to respond to inserts and updates in the container.
Related concept
Read the scenario before looking for a memorised answer.
✗
Blob trigger
Why it's wrong here
Blob trigger is for Azure Blob Storage, not Cosmos DB changes.
✗
Event Grid trigger
Why it's wrong here
Event Grid trigger can handle events from Cosmos DB but requires explicit event publishing; the Cosmos DB trigger is the native approach for change feed.
✗
Service Bus trigger
Why it's wrong here
Service Bus trigger processes messages from a queue or topic, not database changes.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may confuse the Cosmos DB trigger with the Event Grid trigger, thinking Event Grid can directly subscribe to Cosmos DB changes, but Event Grid requires a custom event publisher or a separate Azure service like Azure Functions to bridge the change feed.
Detailed technical explanation
How to think about this question
The Cosmos DB trigger uses the change feed processor library, which reads from the `_lsn` (log sequence number) and `_ts` (timestamp) metadata in the container. It supports leases to track progress across multiple function instances, ensuring at-least-once delivery. In a real-world scenario, if you need to filter for specific operations (e.g., only inserts), you must handle that logic inside the function because the trigger delivers all modifications.
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 for Azure storage — This question tests Develop for Azure storage — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Cosmos DB trigger — A Cosmos DB trigger is the correct choice because it is specifically designed to react to changes in a Cosmos DB container by leveraging the change feed. The Azure Function runtime polls the change feed for inserts and updates, invoking the function with batches of documents as they occur. This provides a native, serverless integration without needing additional services.
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.
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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