Question 836 of 881
AZ-204 Develop Azure compute solutions Practice Question
You are developing an Azure Function that processes messages from an Azure Service Bus queue. The function uses a Service Bus queue trigger and runs on a Consumption Plan. The queue receives a high volume of messages in bursts. You need to ensure that the function scales out to handle the load but does not exceed 10 concurrent instances. Which configuration should you apply?
⚠ Common exam trap
The trap is confusing per-instance concurrency settings (like 'maxConcurrentCalls' in host.json) with the function app's instance-level scale limit ('functionAppScaleLimit'). The question specifically asks to cap the number of concurrent instances.
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
✓
Set the 'functionAppScaleLimit' application setting to 10 in the function app.
The 'functionAppScaleLimit' application setting controls the maximum number of instances for a function app running on the Consumption plan. Setting it to 10 ensures the app does not scale beyond 10 instances. The 'maxConcurrentCalls' property only limits per-instance concurrency.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Set the 'maxConcurrentCalls' property to 10 in the host.json file.
Why it's wrong here
Correct. The maxConcurrentCalls property limits per-instance concurrency to 10, and with the Consumption Plan's scaling, this ensures overall concurrency stays within 10 concurrent executions.
- ✓
Set the 'functionAppScaleLimit' application setting to 10 in the function app.
Why this is correct
Incorrect. The 'WEBSITE_MAX_INSTANCES' application setting is used for App Service plans, not Consumption Plan function apps. For Consumption Plan, instance limits are controlled via the 'functionAppScaleLimit' property, not an app setting.
- ✗
Set the 'maxMessageBatchSize' property to 10 in the host.json file.
Why it's wrong here
Incorrect. The maxMessageBatchSize property controls the number of messages retrieved in a single batch, not the number of concurrent executions or instances.
- ✗
Restrict the Service Bus queue to have a maximum concurrency of 10 at the namespace level.
Why it's wrong here
Incorrect. Restricting concurrency at the Service Bus namespace level affects all consumers on the namespace and is not a function app configuration.
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Last reviewed: Jun 11, 2026
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