- A
Set the 'maxConcurrentCalls' property to 10 in the host.json file.
Why wrong: maxConcurrentCalls limits the number of messages processed concurrently per instance, not the number of instances. Setting it to 10 would not cap total instances.
- B
Set the 'WEBSITE_MAX_INSTANCES' application setting to 10 in the function app.
Correct. The WEBSITE_MAX_INSTANCES setting limits the maximum number of instances that the function app can scale out to. This is the correct way to cap the number of concurrent instances.
- C
Set the 'maxMessageBatchSize' property to 10 in the host.json file.
Why wrong: maxMessageBatchSize specifies the maximum number of messages retrieved per batch per instance. It does not limit the number of instances.
- D
Restrict the Service Bus queue to have a maximum concurrency of 10 at the namespace level.
Why wrong: Service Bus queues do not have a setting to limit concurrency per consumer at the namespace level. The scaling is controlled by the consumer (the function app).
Quick Answer
The correct answer is to set the 'WEBSITE_MAX_INSTANCES' application setting to 10 in the function app. This setting directly limits the maximum number of concurrent instances your Azure Function can scale to on a Consumption Plan, ensuring that even during burst loads from a Service Bus queue, the platform will not allocate more than 10 instances. On the AZ-204 exam, this tests your understanding of scaling controls versus concurrency controls: many candidates mistakenly adjust 'maxConcurrentCalls' (which controls how many messages a single instance processes simultaneously) or 'maxMessageBatchSize' (which controls batch size), but neither caps instance count. The key trap is confusing per-instance concurrency with overall scale-out limits. Remember the mnemonic: "WEBSITE_MAX_INSTANCES is the ceiling for instances; maxConcurrentCalls is the floor for per-instance work."
AZ-204 Develop Azure compute solutions Practice Question
This AZ-204 practice question tests your understanding of develop azure compute solutions. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. 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.
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?
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 'WEBSITE_MAX_INSTANCES' application setting to 10 in the function app.
Option B is correct because the 'WEBSITE_MAX_INSTANCES' application setting is the proper way to limit the number of concurrent instances (scale-out) for a function app running on a Consumption Plan. This setting caps the maximum number of instances the platform can allocate, ensuring that even under high burst loads, the function does not exceed 10 concurrent instances. The Service Bus trigger's 'maxConcurrentCalls' controls per-instance concurrency, not instance count, and 'maxMessageBatchSize' controls batch size, not scaling.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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
maxConcurrentCalls limits the number of messages processed concurrently per instance, not the number of instances. Setting it to 10 would not cap total instances.
- ✓
Set the 'WEBSITE_MAX_INSTANCES' application setting to 10 in the function app.
Why this is correct
Correct. The WEBSITE_MAX_INSTANCES setting limits the maximum number of instances that the function app can scale out to. This is the correct way to cap the number of concurrent instances.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Set the 'maxMessageBatchSize' property to 10 in the host.json file.
Why it's wrong here
maxMessageBatchSize specifies the maximum number of messages retrieved per batch per instance. It does not limit the number of instances.
- ✗
Restrict the Service Bus queue to have a maximum concurrency of 10 at the namespace level.
Why it's wrong here
Service Bus queues do not have a setting to limit concurrency per consumer at the namespace level. The scaling is controlled by the consumer (the function app).
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is confusing per-instance concurrency settings (maxConcurrentCalls) with instance-level scaling limits (WEBSITE_MAX_INSTANCES), leading candidates to incorrectly choose A when the question explicitly asks about limiting concurrent instances, not per-instance message processing.
Detailed technical explanation
How to think about this question
Under the hood, the Consumption Plan uses a scale controller that monitors the Service Bus queue's message count and backlog to decide how many instances to add. The 'WEBSITE_MAX_INSTANCES' setting overrides the default scale-out behavior by imposing an upper bound on the instance count, which is critical for cost control or downstream resource limits. A real-world scenario is when a downstream database can only handle 10 concurrent connections; without this cap, the function could scale to hundreds of instances, overwhelming the database.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
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
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
What to study next
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FAQ
Questions learners often ask
What does this AZ-204 question test?
Develop Azure compute solutions — This question tests Develop Azure compute solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Set the 'WEBSITE_MAX_INSTANCES' application setting to 10 in the function app. — Option B is correct because the 'WEBSITE_MAX_INSTANCES' application setting is the proper way to limit the number of concurrent instances (scale-out) for a function app running on a Consumption Plan. This setting caps the maximum number of instances the platform can allocate, ensuring that even under high burst loads, the function does not exceed 10 concurrent instances. The Service Bus trigger's 'maxConcurrentCalls' controls per-instance concurrency, not instance count, and 'maxMessageBatchSize' controls batch size, not scaling.
What should I do if I get this AZ-204 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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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.
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