AZ-900 Describe Azure architecture and services Practice Question
A company plans to containerize a legacy web application and run it on Azure. The application experiences variable traffic volumes, with periodic spikes during lunch hours and weekends. The company wants the solution to automatically increase the number of running container instances during high demand and reduce them during low demand, without requiring any manual intervention or management of server infrastructure. Which Azure compute service should the company use?
⚠ Common exam trap
Watch out — candidates often confuse Azure Container Instances (ACI) as the go-to for containerized apps, but ACI lacks native autoscaling and is better suited for burstable, short-lived tasks, while Azure App Service provides the required autoscaling and serverless management for containerized web applications with variable traffic.
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 App Service
Azure App Service is correct because it supports containerized web applications with built-in autoscaling capabilities that automatically adjust the number of running container instances based on demand, such as CPU or memory thresholds, without requiring any manual intervention or server management. The platform handles the underlying infrastructure, patching, and load balancing, making it ideal for variable traffic patterns like lunch-hour spikes.
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 App Service
Why this is correct
Azure App Service can run containerized web applications and supports automatic scaling (horizontal scale) based on metrics like HTTP request rate or CPU utilization, without requiring any administrator to manage underlying VMs or orchestration pieces.
- ✗
Azure Container Instances (ACI)
Why it's wrong here
Azure Container Instances provides a simple way to run a container, but it does not have built-in autoscaling based on traffic load. Scaling multiple container groups must be implemented separately, often requiring external logic or additional services.
When this WOULD be correct
A question asking for a simple, fast way to run a single container without managing orchestration, where the workload is predictable or manually scalable, and autoscaling is not a requirement. For example: 'A company needs to run a batch job in a container for a few hours and then stop, with minimal setup.'
- ✗
Azure Kubernetes Service (AKS)
Why it's wrong here
Azure Kubernetes Service (AKS) fails here because the company explicitly requires no management of server infrastructure. While AKS provides robust container orchestration and automatic scaling of container instances, it still necessitates managing the underlying virtual machine node pools. It is tempting as it excels at deploying and managing containerised applications at scale. AKS would be the correct choice for complex microservices architectures needing fine-grained control, custom networking, or specific compute configurations, where some infrastructure management is acceptable for enhanced customisation.
When this WOULD be correct
A company needs to run containerized microservices with complex orchestration, service discovery, and advanced scaling policies, and is willing to manage the cluster or use a managed Kubernetes service with some administrative overhead.
- ✗
Azure Functions
Why it's wrong here
Azure Functions is a serverless compute service designed for event-driven, short-lived functions. It is not intended for hosting long-running containerized web applications, and its scaling model is based on function executions rather than HTTP traffic to a persistent application.
When this WOULD be correct
A company needs to run a small piece of code (e.g., a webhook or API endpoint) that processes events from Azure services (e.g., Blob Storage, Cosmos DB) and automatically scales based on event volume, with no need to manage containers or infrastructure.
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 App ServiceCorrect answer▾
Why this is correct
Azure App Service can run containerized web applications and supports automatic scaling (horizontal scale) based on metrics like HTTP request rate or CPU utilization, without requiring any administrator to manage underlying VMs or orchestration pieces.
✗Azure Container Instances (ACI)Wrong answer — click to see why▾
Why this is wrong here
Azure Container Instances does not provide built-in autoscaling based on traffic metrics; it requires manual scaling or integration with external tools, and it lacks the automatic scaling and load balancing capabilities needed for variable traffic without infrastructure management.
★ When this WOULD be the correct answer
A question asking for a simple, fast way to run a single container without managing orchestration, where the workload is predictable or manually scalable, and autoscaling is not a requirement. For example: 'A company needs to run a batch job in a container for a few hours and then stop, with minimal setup.'
Why candidates choose this
Candidates may think ACI is suitable because it is a container service that can run containers without managing servers, but they overlook that it does not natively support automatic scaling based on demand, which is a key requirement in the question.
✗Azure Kubernetes Service (AKS)Wrong answer — click to see why▾
Why this is wrong here
AKS requires management of the Kubernetes cluster (e.g., node pools, scaling policies) and is not fully serverless; it does not meet the requirement of zero manual intervention for infrastructure management.
★ When this WOULD be the correct answer
A company needs to run containerized microservices with complex orchestration, service discovery, and advanced scaling policies, and is willing to manage the cluster or use a managed Kubernetes service with some administrative overhead.
Why candidates choose this
Candidates may associate container orchestration and auto-scaling with Kubernetes, overlooking that AKS still involves cluster management, unlike the fully managed, serverless auto-scaling offered by App Service.
✗Azure FunctionsWrong answer — click to see why▾
Why this is wrong here
Azure Functions is event-driven and designed for short-lived, stateless workloads, not for running containerized legacy web applications with variable traffic. It lacks native support for running arbitrary containers and does not provide the same scaling and management capabilities for containerized apps as App Service.
★ When this WOULD be the correct answer
A company needs to run a small piece of code (e.g., a webhook or API endpoint) that processes events from Azure services (e.g., Blob Storage, Cosmos DB) and automatically scales based on event volume, with no need to manage containers or infrastructure.
Why candidates choose this
Candidates may confuse serverless computing with container orchestration, thinking that Azure Functions can run any containerized workload and auto-scale, but Functions is optimized for code snippets, not full containerized applications.
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?”
Go deeper
Related to this question
Learn chapter
Azure Regions and Geographies
Key term
Azure App Service
Azure App Service is a fully managed platform for building, deploying, and scaling web applications and APIs without managing the underlying infrastructure.
Key term
Container
A container is a lightweight, standalone software package that includes everything needed to run an application, such as code, runtime, system tools, and libraries.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.