- A
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.
- B
Function chaining: call each activity function sequentially, collecting each result before starting the next
Why wrong: 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.
- C
Async HTTP API: start the workflow with an HTTP trigger, return a 202 with a status URL, and have the client poll for completion
Why wrong: 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.
- D
Monitor: use a Durable timer loop that checks a status table every 60 seconds until all records are marked processed
Why wrong: 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.
Quick Answer
The correct choice is the fan-out/fan-in pattern, because it uses `Task.WhenAll` inside a durable orchestrator to launch 500 activity functions in parallel and then aggregate all returned results into a single summary report. This pattern directly satisfies the requirement for parallel processing and aggregation, while the orchestration’s state is durably persisted in Azure Storage, allowing it to resume seamlessly after a Function App restart. On the AZ-204 exam, this scenario tests your understanding of how Durable Functions manage long-running, stateful workflows—common traps include confusing fan-out/fan-in with the chaining pattern (sequential execution) or the monitor pattern (polling). Remember that fan-out/fan-in is the go-to for any “process many items in parallel, then combine” requirement, and the key memory tip is “scatter-gather”: scatter work across activities, then gather results with `Task.WhenAll`.
AZ-204 Practice Question: Durable Functions fan-out/fan-in for parallel…
This AZ-204 practice question tests your understanding of develop azure compute solutions. 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
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Fan-out/fan-in: start 500 activity functions in parallel with Task.WhenAll inside the orchestrator, then aggregate all returned results
Option A is correct because the fan-out/fan-in pattern in Durable Functions is specifically designed to execute multiple activity functions in parallel using Task.WhenAll inside an orchestrator, then aggregate their results. This matches the requirement to process 500 customer records concurrently and produce a single summary report, while the orchestration state is durably persisted and can resume after a Function App restart.
Key principle: Durable Functions
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Fan-out/fan-in: start 500 activity functions in parallel with Task.WhenAll inside the orchestrator, then aggregate all returned results
Why this is correct
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.
Related concept
Durable Functions
- ✗
Function chaining: call each activity function sequentially, collecting each result before starting the next
Why it's wrong here
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.
- ✗
Async HTTP API: start the workflow with an HTTP trigger, return a 202 with a status URL, and have the client poll for completion
Why it's wrong here
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.
- ✗
Monitor: use a Durable timer loop that checks a status table every 60 seconds until all records are marked processed
Why it's wrong here
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may confuse the fan-out/fan-in pattern with the Async HTTP API pattern, thinking that the HTTP trigger and status polling are required for parallel processing, but the key distinction is that fan-out/fan-in handles the parallel execution and aggregation within the orchestrator itself, not via external polling.
Detailed technical explanation
How to think about this question
Under the hood, the fan-out/fan-in pattern leverages the Durable Task Framework's replay mechanism, where the orchestrator function schedules all 500 activity functions simultaneously via Task.WhenAll, and the orchestration history is checkpointed after each activity completes. This ensures that if the Function App restarts, the orchestrator replays from the last checkpoint, resuming only the incomplete activities, making it resilient to failures. In a real-world scenario, this pattern is ideal for batch processing jobs like nightly report generation where each record is independent and results must be combined.
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
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. Durable Functions Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
Review durable Functions, then practise related AZ-204 questions on the same topic to reinforce the concept.
- →
Develop Azure compute solutions — study guide chapter
Learn the concepts, then practise the questions
- →
Develop Azure compute solutions practice questions
Targeted practice on this topic area only
- →
All AZ-204 questions
997 questions across all exam domains
- →
Microsoft Azure Developer Associate AZ-204 study guide
Full concept coverage aligned to exam objectives
- →
AZ-204 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Related AZ-204 practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Develop Azure compute solutions practice questions
Practise AZ-204 questions linked to Develop Azure compute solutions.
Develop for Azure storage practice questions
Practise AZ-204 questions linked to Develop for Azure storage.
Implement Azure security practice questions
Practise AZ-204 questions linked to Implement Azure security.
Connect to and consume Azure services and third-party services practice questions
Practise AZ-204 questions linked to Connect to and consume Azure services and third-party services.
Monitor, troubleshoot, and optimize Azure solutions practice questions
Practise AZ-204 questions linked to Monitor, troubleshoot, and optimize Azure solutions.
AZ-204 fundamentals practice questions
Practise AZ-204 questions linked to AZ-204 fundamentals.
AZ-204 scenario practice questions
Practise AZ-204 questions linked to AZ-204 scenario.
AZ-204 troubleshooting practice questions
Practise AZ-204 questions linked to AZ-204 troubleshooting.
Practice this exam
Start a free AZ-204 practice session
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Questions learners often ask
What does this AZ-204 question test?
Develop Azure compute solutions — This question tests Develop Azure compute solutions — 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 — Option A is correct because the fan-out/fan-in pattern in Durable Functions is specifically designed to execute multiple activity functions in parallel using Task.WhenAll inside an orchestrator, then aggregate their results. This matches the requirement to process 500 customer records concurrently and produce a single summary report, while the orchestration state is durably persisted and can resume after a Function App restart.
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.
What is the key concept behind this question?
Durable Functions
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Keep practising
More AZ-204 practice questions
- An app must store relational state and perform transactions across multiple tables with T-SQL support. Which Azure data…
- You are monitoring an Azure App Service using Application Insights. You notice that the server response time is high for…
- Which TWO services can be used to implement a publish-subscribe messaging pattern in Azure?
- You need to monitor the CPU utilization of an Azure VM in real-time and set up an alert when it exceeds 90%. Which Azure…
- You are monitoring an Azure web application with Application Insights. You notice a sudden increase in the number of fai…
- You are monitoring an Azure web app using Application Insights. You need to create a query that returns the average dura…
Last reviewed: Jun 11, 2026
This AZ-204 practice question is part of Courseiva's free Microsoft certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the AZ-204 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.