AZ-900 Describe Azure architecture and services Practice Question

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 Virtual Machines

  Why it's wrong here

  Azure Virtual Machines (VMs) give you Infrastructure-as-a-Service (IaaS), offering full control over the guest OS, middleware, and application stack, but that control comes with significant management overhead. You are responsible for patching the OS, installing and updating software, and configuring load balancers and scaling rules—often requiring Azure VM Scale Sets to implement auto-scaling, which adds setup complexity and ongoing maintenance. Unlike App Service, a single VM does not automatically scale based on demand; you must design and manage the infrastructure to do so, making it less suitable for a simple web-app requirement of automatic scaling.

  When this WOULD be correct

  A company needs full control over the operating system, custom software, or specific configurations that are not supported by PaaS; they are willing to manage VMs and infrastructure.

• ✓

  Azure App Service

  Why this is correct

  Azure App Service is a fully managed Platform-as-a-Service (PaaS) offering built for hosting web applications, REST APIs, and mobile back ends. It includes automatic scaling out (increasing instances) and in (decreasing instances) based on rules you define, such as CPU usage, memory, or request count, without any manual intervention. Azure App Service also manages the underlying OS, runtime patches, and load balancing, making it the simplest and most appropriate choice for a web app that needs to scale automatically with demand.

• ✗

  Azure Functions

  Why it's wrong here

  Azure Functions is a serverless compute service designed for event-driven, short-lived workloads, such as processing queue messages, responding to HTTP triggers, or handling timers. Although it can host HTTP endpoints, it does not provide a persistent web application runtime with features like WebJobs or managed web server sessions; each function executes independently and scales per invocation, not as a full web application. Running a traditional web app on Azure Functions would require restructuring it into discrete functions and you lose built-in support for complex routing, static file hosting, and sticky sessions—making it a poor fit for a complete, continuously running website.

  When this WOULD be correct

  A company needs to run code in response to events (e.g., HTTP requests, queue messages, timers) without managing servers, and the code is expected to execute in short bursts. For example: 'Which Azure service should be used to automatically resize images when uploaded to Blob Storage?'

• ✗

  Azure Container Instances

  Why it's wrong here

  Azure Container Instances (ACI) allows you to run containers in the cloud without provisioning VMs, but it does not include a built-in automatic scaling mechanism for web apps. ACI scales containers by manually creating or deleting container groups; there is no native rule-based scaling based on metrics like CPU or HTTP traffic. To achieve auto-scaling with ACI, you would need to pair it with Azure Container Apps, a Kubernetes orchestrator, or a custom scheduler, whereas Azure App Service provides auto-scaling out of the box for web deployments.

  When this WOULD be correct

  A company wants to deploy containerized applications without managing the underlying VMs or orchestrator, and they are willing to package their code into containers. They need fast startup times and per-second billing.

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.

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?”