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AZ-204 Practice Question: Cosmos DB change feed processor for scalable…
This AZ-204 practice question tests your understanding of cosmos db change feed processor for scalable…. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: cosmos DB change feed. 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.
An e-commerce platform writes orders to a Cosmos DB container. A downstream inventory service must process every new or updated order exactly once, even if the inventory service restarts mid-batch. The solution must scale horizontally when order volume increases. What is the recommended design?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Distractor review
Subscribe to Azure Event Grid Cosmos DB events and process them in an Azure Function
Azure Event Grid does not natively emit per-document Cosmos DB change events at the document level in a way that supports the exactly-once-with-checkpoint semantics required. The change feed processor is the supported pattern for this use case.
B
Distractor review
Enable Cosmos DB analytical store and run batch queries from an Azure Synapse Spark pool every hour
The analytical store serves OLAP workloads with high latency (minutes to hours). The inventory service needs near-real-time processing after each order write. Spark batch queries are unsuitable for event-driven, low-latency inventory updates.
C
Best answer
Use the change feed processor library with a dedicated lease container; each worker instance claims partition leases and commits checkpoints after processing each batch
The lease container stores the last-processed continuation token per partition. On restart, a worker reads its leases and resumes from the checkpointed position. Adding more worker instances automatically redistributes leases across instances, providing linear horizontal scaling.
D
Distractor review
Poll the Cosmos DB container every 30 seconds using a _ts timestamp filter to find recently modified documents
Timestamp polling has two problems: clock skew can cause missed documents near the query boundary, and repeated full-container scans increase RU consumption. The change feed is a purpose-built, push-based stream that avoids both issues.
Common exam trap
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.
Technical deep dive
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- Cosmos DB change feed
- change feed processor
- lease container
- at-least-once delivery
- horizontal scaling
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
Cosmos DB change feed
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Question 5
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Question 6
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FAQ
Questions learners often ask
What does this AZ-204 question test?
Cosmos DB change feed
What is the correct answer to this question?
The correct answer is: Use the change feed processor library with a dedicated lease container; each worker instance claims partition leases and commits checkpoints after processing each batch — The Cosmos DB change feed processor library uses a lease container to track per-partition progress. Each worker instance claims leases for one or more partitions. If a worker restarts, it resumes from the last committed lease checkpoint rather than reprocessing from the beginning. Multiple workers can share the load by taking different leases, enabling horizontal scaling. This is the canonical pattern for event-driven consumption from Cosmos DB.
What should I do if I get this AZ-204 question wrong?
Review cosmos DB change feed, then practise related AZ-204 questions on the same topic to reinforce the concept.
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