Question 256 of 981
AZ-900 Describe Azure architecture and services Practice Question
A company is developing a REST API that processes incoming HTTP requests. The API usage is highly unpredictable; sometimes it receives thousands of requests per minute, and at other times it receives zero requests for hours. The company wants to pay only for the compute time consumed when the API code is actually executing. They also want Microsoft to automatically handle scaling and maintenance of the underlying server infrastructure. Which Azure compute service should the company use?
⚠ Common exam trap
Test-takers frequently confuse Azure Functions with Azure App Service or Container Instances, assuming any 'serverless' or 'pay-per-use' label applies, but fail to recognize that only the Consumption plan of Azure Functions provides true zero-cost idle time and automatic scaling without manual configuration.
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 (Consumption plan)
Azure Functions with the Consumption plan is the correct choice because it is a serverless compute service that executes code only when triggered by incoming HTTP requests, automatically scaling to handle unpredictable workloads. The Consumption plan charges only for the compute time consumed during execution, with no cost when the function is idle, and Microsoft fully manages the underlying infrastructure, including scaling and maintenance.
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 (Consumption plan)
Why this is correct
Correct. Azure Functions Consumption plan is a serverless, event-driven compute service. It automatically scales based on incoming HTTP requests and bills only for the time the function code executes. When there are no requests, there is no cost.
- ✗
Azure App Service (Basic tier)
Why it's wrong here
Incorrect. Azure App Service runs continuously on dedicated virtual machines even when no requests are processed. It incurs cost for the running VMs regardless of usage, and it does not align with the 'pay only for execution time' requirement.
When this WOULD be correct
A company needs to host a web application that requires consistent performance, custom domain, SSL, and minimal cold-start latency, with predictable traffic that justifies a fixed monthly cost.
- ✗
Azure Container Instances
Why it's wrong here
Azure Container Instances are not event-driven by default; a container group is provisioned and remains running until explicitly stopped or restarted, so you are billed for the allocated vCPU and memory for the entire time it exists. Although ACI uses per-second billing, that still means paying for idle time when no HTTP requests are arriving, because the container continuously consumes resources. ACI also lacks a built-in scale-to-zero behavior; you would need an external orchestrator like Kubernetes with KEDA to scale it down, which is not equivalent to the automatic, per-execution billing model of Azure Functions Consumption.
When this WOULD be correct
A company needs to run a Docker containerized application that must start quickly (under a minute) and run for a few minutes to hours, with no need for orchestration or scaling. They want to pay only for the container's running time, not for underlying VMs.
- ✗
Azure Logic Apps
Why it's wrong here
Incorrect. Azure Logic Apps is a serverless workflow and integration service, but it is not designed to host REST APIs. It uses connectors and triggers for business process automation and does not provide direct HTTP API handling with custom code execution.
When this WOULD be correct
A company needs to automate a business workflow that integrates multiple SaaS applications and on-premises systems, such as automatically sending an email when a new file is uploaded to SharePoint. The solution should be low-code and triggered by events, with pay-per-execution pricing.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The AZ-900 exam frequently reuses these exact scenarios with slightly different constraints.
✓Azure Functions (Consumption plan)Correct answer▾
Why this is correct
Correct. Azure Functions Consumption plan is a serverless, event-driven compute service. It automatically scales based on incoming HTTP requests and bills only for the time the function code executes. When there are no requests, there is no cost.
✗Azure App Service (Basic tier)Wrong answer — click to see why▾
Why this is wrong here
The Basic tier of Azure App Service runs continuously on dedicated VMs, incurring costs even when no requests are processed, and does not provide automatic scaling to zero or consumption-based billing.
★ When this WOULD be the correct answer
A company needs to host a web application that requires consistent performance, custom domain, SSL, and minimal cold-start latency, with predictable traffic that justifies a fixed monthly cost.
Why candidates choose this
Candidates may confuse App Service with serverless offerings because it supports continuous deployment and auto-scaling, but overlook that it does not scale to zero and charges for allocated resources, not actual execution time.
✗Azure Container InstancesWrong answer — click to see why▾
Why this is wrong here
Azure Container Instances charges for the entire duration the container is running, not per execution, and does not automatically scale to zero when idle, so it does not meet the pay-per-execution requirement.
★ When this WOULD be the correct answer
A company needs to run a Docker containerized application that must start quickly (under a minute) and run for a few minutes to hours, with no need for orchestration or scaling. They want to pay only for the container's running time, not for underlying VMs.
Why candidates choose this
Candidates may think container instances are serverless and pay-per-use, but they misunderstand that billing is per second of container runtime, not per function execution, and they don't auto-scale to zero.
✗Azure Logic AppsWrong answer — click to see why▾
Why this is wrong here
Azure Logic Apps is a workflow orchestration service that runs on a consumption plan, but it is designed for integrating systems and automating business processes, not for executing custom code like a REST API. The question specifies the need to process HTTP requests with custom code, which is better suited for Azure Functions.
★ When this WOULD be the correct answer
A company needs to automate a business workflow that integrates multiple SaaS applications and on-premises systems, such as automatically sending an email when a new file is uploaded to SharePoint. The solution should be low-code and triggered by events, with pay-per-execution pricing.
Why candidates choose this
Candidates may confuse Azure Logic Apps with Azure Functions because both are serverless and can be triggered by HTTP requests, but they overlook that Logic Apps is primarily for orchestration and integration, not for running custom code.
Analysis generated from the official AZ-900blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Quick reference
Cloud Service Model Comparison
| Model | You Manage | Provider Manages | Examples |
|---|---|---|---|
| IaaS | OS, runtime, apps, data | Hardware, hypervisor, networking | EC2, Azure VMs, GCP Compute Engine |
| PaaS | Apps and data | OS, runtime, middleware, hardware | Elastic Beanstalk, Azure App Service |
| SaaS | Data and settings only | Everything else | Microsoft 365, Salesforce, Workday |
| FaaS / Serverless | Function code only | Infra, scaling, runtime | Lambda, Azure Functions, Cloud Run |
| CaaS | Containers and apps | Kubernetes, OS, hardware | EKS, AKS, GKE |
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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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