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AZ-204 Practice Question: Durable Functions fan-out/fan-in for parallel…
This AZ-204 practice question tests your understanding of durable functions fan-out/fan-in for parallel…. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. A key principle to apply: durable Functions. 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.
A workflow must process 500 customer records in parallel and then aggregate all results into a single summary report. The team wants to use Azure Durable Functions so the orchestration state is durable and the solution can resume after a Function App restart. Which Durable Functions pattern matches this requirement?
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
Async HTTP API: start the workflow with an HTTP trigger, return a 202 with a status URL, and have the client poll for completion
The Async HTTP API pattern is an interaction model for client-facing orchestrations. It describes how a client tracks workflow progress via polling — it is not a parallelism pattern. The fan-out/fan-in pattern describes how the orchestration itself processes records.
B
Distractor review
Monitor: use a Durable timer loop that checks a status table every 60 seconds until all records are marked processed
The Monitor pattern polls external state at intervals — it's suitable for tracking external processes. It does not initiate parallel processing. Using it to wait for 500 individually triggered activities to complete would be architecturally inverted and inefficient.
C
Best answer
Fan-out/fan-in: start 500 activity functions in parallel with Task.WhenAll inside the orchestrator, then aggregate all returned results
Task.WhenAll fires all 500 activities simultaneously (constrained by the configured max concurrency). The orchestrator yields at the await statement, checkpointing its state. When all activities complete, the orchestrator resumes and aggregates results. Durable state management handles host restarts transparently.
D
Distractor review
Function chaining: call each activity function sequentially, collecting each result before starting the next
Function chaining processes records one at a time. For 500 records, this serializes all processing and provides no parallelism. The workflow would take 500 times as long as the parallel fan-out approach.
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
- Durable Functions
- fan-out/fan-in pattern
- Task.WhenAll
- orchestrator function
- parallel activity execution
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
Durable Functions
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FAQ
Questions learners often ask
What does this AZ-204 question test?
Durable Functions
What is the correct answer to this question?
The correct answer is: Fan-out/fan-in: start 500 activity functions in parallel with Task.WhenAll inside the orchestrator, then aggregate all returned results — The fan-out/fan-in pattern uses an orchestrator function to start N activity functions in parallel using Task.WhenAll (C#) or context.df.Task.all (JS). The orchestrator yields until all activities complete, then aggregates results. Durable Functions replay history to reconstruct orchestrator state after restarts — activity results are persisted in the task hub, so in-progress workflows survive host restarts. Fan-out/fan-in is purpose-built for exactly this parallel aggregation pattern.
What should I do if I get this AZ-204 question wrong?
Review durable Functions, then practise related AZ-204 questions on the same topic to reinforce the concept.
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