AZ-204 Develop Azure compute solutions Practice Question
A Durable Functions workflow for a booking backend must call five independent activity functions and continue only after all results are available. Which pattern is appropriate?
⚠ Common exam trap
Candidates often confuse the fan-out/fan-in pattern with function chaining, mistakenly thinking that sequential execution is sufficient, or they incorrectly apply the Monitor pattern when the requirement is simply parallel execution without polling.
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
The fan-out/fan-in pattern is designed for scenarios where multiple independent tasks must execute in parallel, and the workflow must wait for all results before proceeding. In Durable Functions, this is implemented using `Task.WhenAll()` to fan out activity function calls and then aggregate their results, which matches the requirement of calling five independent activities and continuing only after all results are available.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Monitor pattern
Why it's wrong here
The monitor pattern polls a recurring condition in a loop, suited to waiting for state changes rather than executing five activities in parallel and joining results. It tempts for long-running status checks. Fan-out/fan-in is required to fan out activities and aggregate all outputs before proceeding.
- ✓
Fan-out/fan-in
Why this is correct
Fan-out/fan-in dispatches multiple activity functions concurrently via `Task.WhenAll`, then aggregates their results once every task completes. This satisfies the stem's requirement to call five independent activities and continue only after all results are available, rather than chaining them sequentially or waiting on a single external event.
- ✗
Human interaction
Why it's wrong here
Human interaction pauses the orchestrator awaiting an external approval or event, adding no mechanism to run five activities concurrently and aggregate their results. It tempts when workflows need manual sign-off. Fan-out/fan-in is required to dispatch parallel activities and wait for all to finish.
- ✗
Function chaining
Why it's wrong here
Function chaining invokes activities sequentially, each awaiting the previous, so five independent calls would run one after another rather than concurrently. It tempts because chaining is the standard Durable Functions pattern for ordered steps. Fan-out/fan-in is required when parallel activities must all complete before continuing.
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