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

  Azure App Service is a platform-as-a-service (PaaS) offering for hosting web applications, REST APIs, and mobile backends. It automatically manages the underlying OS, patches, and infrastructure, giving you no remote desktop access or ability to customize the operating system kernel or install global software. While you can adjust application settings and use a sandboxed file system, you cannot run a legacy application that requires kernel-level privileges or persistent custom OS configuration, making it inappropriate for full control.

  When this WOULD be correct

  A company needs to deploy a web application or API with built-in auto-scaling and high availability, without managing the underlying OS. For example, running a Node.js or .NET Core web app with automatic patching.

• ✗

  Azure Functions

  Why it's wrong here

  Azure Functions is a serverless compute service that executes event-driven code without requiring you to provision or manage any underlying virtual machines or operating systems. For a legacy application that needs full control over the OS, this service is unsuitable because it only supports specific runtime stacks (e.g., Node.js, .NET Core, Python) and enforces strict execution time and resource limits. You cannot install arbitrary dependencies, modify the host OS, or run long-lived processes, so the application's control requirements cannot be met.

  When this WOULD be correct

  A company needs to run event-driven code that scales automatically without managing infrastructure, such as processing messages from a queue or responding to HTTP triggers, and does not require OS-level control.

• ✓

  Azure Virtual Machines

  Why this is correct

  Azure Virtual Machines provide infrastructure-as-a-service (IaaS) where you deploy a full guest operating system that you manage entirely. You have administrative access to the OS, can install custom software, configure kernel-level settings (if using Linux or Windows with appropriate access), and run legacy applications that depend on specific OS versions or low-level system calls. Additionally, you can use Availability Zones or Availability Sets to achieve high availability for the VM-based workload. This level of control is unmatched by PaaS or serverless offerings.

• ✗

  Azure Container Instances

  Why it's wrong here

  Azure Container Instances (ACI) provides a fast and simple way to run containers in Azure without managing VMs, but it abstracts the underlying host OS entirely. Containers share the host OS kernel, and you cannot access or modify that kernel; you only manage the user-space processes defined in the container image. For a legacy application requiring full control over the OS, for instance, installing custom device drivers or changing sysctl parameters, ACI's kernel-sharing model and lack of host-level access are limiting, so it falls short of VM-level control.

  When this WOULD be correct

  A company needs to quickly deploy and run a containerized application without managing underlying servers, and requires per-second billing and fast startup times. The application does not need OS-level customization or high availability across multiple instances.

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?”

Go deeper

Related to this question