AZ-900 Describe Azure architecture and services Practice Question
Which Azure service allows you to run Linux and Windows virtual machines in the cloud with full control over the operating system?
⚠ Common exam trap
Many candidates confuse PaaS services like App Service or serverless Functions with IaaS VMs, mistakenly thinking they can control the OS in those services when in fact they only control the application code.
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 Virtual Machines
Azure Virtual Machines (IaaS) provide full control over the guest operating system, including the ability to install custom software, configure the kernel, and manage updates. This is the only service in the list that offers direct access to the OS for both Linux and Windows, as it runs on a hypervisor-managed virtual hardware stack.
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 PaaS offering for hosting web apps, REST APIs, and mobile backends. While you can deploy code or containers, Azure fully owns the underlying host OS, including patches and security updates, and you never get direct access to the OS layer—no remote desktop, registry, or file-system control. This makes it unsuitable for workloads that rely on OS-level customization or system-level configuration, since all administration is limited to application settings and deployment slots.
- ✓
Azure Virtual Machines
Why this is correct
Azure Virtual Machines is an IaaS offering that gives you complete control over the guest OS—Windows or Linux—including the kernel, installed software, patching, and OS-level configuration. You can run any workload that requires full OS access, such as legacy applications that need Windows services, custom drivers, or OS ACLs, without rearchitecting. The other options abstract or containerize the runtime and do not expose an OS that you can directly manage.
- ✗
Azure Container Instances
Why it's wrong here
Azure Container Instances (ACI) runs containers in a serverless fashion, but you only manage the container image, environment variables, and logs—not the underlying OS. Containers share the host OS kernel, so you cannot install or configure the OS from inside the container, and ACI gives you no access to the underlying virtual machine. This means it is wrong because it abstracts the host OS entirely and is meant for containerized applications, not workloads requiring OS-level management.
- ✗
Azure Functions
Why it's wrong here
Azure Functions is a serverless compute service where you deploy only your code (or a function app) and the runtime is wholly managed by Azure. There is no OS to patch, no virtual machine to RDP into, and no container to maintain; scaling is event-driven and per-execution, with dependencies supplied through app settings or bundled libraries. Because your control ends at the code level, any workload that needs direct OS interaction or a persistent guest environment cannot be run on Functions, making it the furthest from IaaS.
Go deeper
Related to this question
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Azure Regions and Geographies
Key term
Hypervisor
A hypervisor is software that creates and runs virtual machines by allowing multiple operating systems to share a single hardware host.
Key term
IaaS
IaaS stands for Infrastructure as a Service, which means renting virtual computing resources like servers, storage, and networking from a cloud provider instead of buying and managing physical hardware yourself.
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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.