- A
Azure Functions
Correct. Azure Functions is a serverless compute service that automatically scales based on demand and charges only for execution time. It can scale to zero when idle, exactly matching the requirements.
- B
Azure App Service
Why wrong: Incorrect. Azure App Service can autoscale, but in most plans it requires at least one instance running continuously (always-on). It does not scale to zero and you incur charges even when no requests are processed.
- C
Azure Kubernetes Service (AKS)
Why wrong: Incorrect. AKS is a container orchestration service that runs on virtual machines. You are responsible for managing the node pool (VMs) and paying for the underlying compute resources even when no containers are running. It does not scale to zero and is not a serverless solution in its standard form.
- D
Azure Virtual Machines
Why wrong: Incorrect. Azure Virtual Machines require you to manage the operating system and scaling configuration. Even if you use VM scale sets with autoscale, the VMs remain allocated and incur costs even when idle. Scaling to zero is not possible without manually deallocating all VMs.
Quick Answer
The answer is Azure Functions, the serverless compute service that automatically scales from zero for unpredictable HTTP traffic. This is correct because Azure Functions runs on a consumption plan, where the service dynamically spins up instances only when an HTTP request arrives and scales down to zero during idle periods, charging you solely for the compute time consumed while your code executes. On the Microsoft Azure Fundamentals AZ-900 exam, this scenario tests your understanding of serverless versus Infrastructure as a Service (IaaS) or Platform as a Service (PaaS) models—a common trap is confusing Azure Functions with Azure App Service, which requires always-on infrastructure. Remember the key distinction: if the question emphasizes “no infrastructure management,” “pay only when code runs,” and “scale from zero,” the answer is always a serverless service like Azure Functions. A helpful memory tip is “Functions for funky traffic”—when traffic is unpredictable and spikes suddenly, think of Azure Functions as the elastic, cost-efficient choice that handles the burst without any manual scaling.
AZ-900 Describe Azure architecture and services Practice Question
This AZ-900 practice question tests your understanding of describe azure architecture and services. 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. 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.
A company is building a mobile app backend that handles HTTP requests from thousands of users. The traffic pattern is highly unpredictable: there can be sudden spikes to hundreds of requests per second followed by long periods of no activity. The development team wants a solution that automatically scales from zero to hundreds of instances based on demand, and they want to pay only for the compute time consumed when the code is actually executing. They do not want to manage any underlying infrastructure, such as virtual machines or containers. Which Azure compute service should they choose?
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
Azure Functions
Azure Functions is the correct choice because it is a serverless compute service that automatically scales from zero to hundreds of instances based on incoming HTTP requests, and you pay only for the compute time consumed when your code executes. It handles unpredictable traffic patterns with sudden spikes and idle periods without requiring any infrastructure management, as it runs on a consumption plan that provides dynamic 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.
- ✓
Azure Functions
Why this is correct
Correct. Azure Functions is a serverless compute service that automatically scales based on demand and charges only for execution time. It can scale to zero when idle, exactly matching the requirements.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Azure App Service
Why it's wrong here
Incorrect. Azure App Service can autoscale, but in most plans it requires at least one instance running continuously (always-on). It does not scale to zero and you incur charges even when no requests are processed.
- ✗
Azure Kubernetes Service (AKS)
Why it's wrong here
Incorrect. AKS is a container orchestration service that runs on virtual machines. You are responsible for managing the node pool (VMs) and paying for the underlying compute resources even when no containers are running. It does not scale to zero and is not a serverless solution in its standard form.
- ✗
Azure Virtual Machines
Why it's wrong here
Incorrect. Azure Virtual Machines require you to manage the operating system and scaling configuration. Even if you use VM scale sets with autoscale, the VMs remain allocated and incur costs even when idle. Scaling to zero is not possible without manually deallocating all VMs.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse Azure Functions with Azure App Service, assuming both can scale to zero, but App Service requires always-on resources and cannot scale down to zero instances, whereas Functions on a consumption plan can.
Detailed technical explanation
How to think about this question
Azure Functions on the Consumption plan uses a dynamic scaling controller that monitors the number of incoming HTTP requests via the Functions host and adds or removes function app instances based on a trigger threshold (e.g., one instance per 200 requests). Under the hood, the Azure Functions runtime relies on the Azure WebJobs SDK and the Azure Storage queue to coordinate scaling, and the billing granularity is per execution (measured in 1-ms increments) with a minimum of 100 ms per execution. In a real-world scenario, a mobile app backend with sporadic spikes would benefit from this model because the function app can scale out to hundreds of instances within seconds during a spike and then scale back to zero when idle, avoiding any idle compute costs.
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-900 question test?
Describe Azure architecture and services — This question tests Describe Azure architecture and services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Azure Functions — Azure Functions is the correct choice because it is a serverless compute service that automatically scales from zero to hundreds of instances based on incoming HTTP requests, and you pay only for the compute time consumed when your code executes. It handles unpredictable traffic patterns with sudden spikes and idle periods without requiring any infrastructure management, as it runs on a consumption plan that provides dynamic scaling.
What should I do if I get this AZ-900 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.
About these practice questions
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Last reviewed: Jun 11, 2026
This AZ-900 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-900 exam.
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