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 App Service

  Why it's wrong here

  App Service is a PaaS offering that manages the OS. Customers cannot install custom software or configure the Windows firewall at the OS level. It is suitable for web apps but not for full administrative access.

  When this WOULD be correct

  A company needs to deploy a web application built on .NET or Node.js that does not require OS-level access, and they want automatic scaling and patching. Azure App Service would be the correct choice for such a PaaS scenario.

• ✓

  Azure Virtual Machines

  Why this is correct

  Azure Virtual Machines provides infrastructure as a service (IaaS) where you deploy a full virtualized Windows Server OS instance with dedicated vCPUs, memory, and disk. This grants complete administrative control to install any custom-built application, modify registry settings, enable Windows roles or features, and configure the built-in Windows Defender Firewall or third-party security tools. You can also place multiple VM instances in an availability set or zone to achieve high availability for the application, making this the only option that delivers true guest OS-level access equivalent to a physical server.

• ✗

  Azure Functions

  Why it's wrong here

  Azure Functions is a serverless, event-driven compute service that executes a single piece of code in response to triggers like HTTP requests or queue messages, with the platform automatically managing and scaling the underlying infrastructure. There is no persistent Windows OS instance to log into, install software, or configure firewall rules, and the execution environment is short-lived and stateless unless you attach external storage. This makes it unsuitable for a full custom-built Windows application that requires continuous uptime, administrative access, and the ability to run background services or long-running processes.

  When this WOULD be correct

  A company needs to run a lightweight, event-driven script that processes messages from a queue and scales automatically based on demand, without managing any infrastructure. Azure Functions would be the correct choice for this serverless, stateless workload.

• ✗

  Azure Container Instances

  Why it's wrong here

  Azure Container Instances runs containers in a managed environment that isolates processes but shares the underlying host OS kernel, meaning you cannot install a separate Windows OS instance or manage Windows Firewall, Windows Update, or device drivers from inside the container. While a Windows container can use a Windows base image, administrative access to the host is not possible, and any OS configuration is limited to what the container image exposes. This falls short for a custom application that requires full OS-level control, such as kernel-level modifications or direct hardware interaction.

  When this WOULD be correct

  A company needs to run a containerized application that is stateless and can be started quickly on demand, without managing underlying VMs or orchestrators. For example, a batch processing job that runs for a few minutes and then stops.

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?”