MS-900 Describe cloud concepts Practice Question
A company runs a virtual machine in Azure that hosts a web application. The company is responsible for configuring the operating system, installing web server software, and managing application updates. The cloud provider is responsible for the physical hardware, networking, and data center security. Which cloud service model does this represent?
⚠ Common exam trap
Candidates often confuse PaaS with IaaS because both involve deploying applications, but the key differentiator is whether the customer manages the OS and installed software—PaaS abstracts the OS, while IaaS does not.
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
✓
Infrastructure as a Service (IaaS)
This scenario describes Infrastructure as a Service (IaaS) because the customer manages the operating system, web server software, and application updates, while the cloud provider handles the physical hardware, networking, and data center security. In IaaS, the provider offers virtualized computing resources over the internet, and the customer retains control over the guest OS and installed software, which matches the responsibilities outlined.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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Software as a Service (SaaS)
Why it's wrong here
Software as a Service (SaaS) delivers a fully managed application, where the provider handles everything from the underlying infrastructure to the OS, middleware, and data, and the customer only configures usage. Running a web app on a virtual machine would not be SaaS because Microsoft or another vendor would not be managing your VM's OS or the app itself. You would retain responsibility for the VM at the OS and application layers, which is outside the SaaS model.
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Platform as a Service (PaaS)
Why it's wrong here
Platform as a Service (PaaS) abstracts the underlying infrastructure and provides a managed runtime for code, so you'd deploy your web app directly to a hosting service without managing a VM or its OS. In the scenario, the company runs a virtual machine, meaning they control and patch the OS and middleware, which is exactly the level of control PaaS would eliminate. With PaaS, you'd typically use something like Azure App Service, not a dedicated VM.
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Infrastructure as a Service (IaaS)
Why this is correct
Infrastructure as a Service (IaaS) provides virtualized computing resources over the internet, where the cloud provider supplies the physical hardware, virtualization, networking, and storage, but you are responsible for installing and managing the guest OS, middleware, and applications. For a VM hosting a web app, IaaS matches because you manage the OS, apply patches, configure the web server, and maintain the app itself. Azure Virtual Machines is a classic IaaS offering that gives you full administrative control.
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Function as a Service (FaaS)
Why it's wrong here
Function as a Service (FaaS) is a serverless execution model where you upload functions that run in response to events, and the provider fully manages servers, scaling, and capacity. You never operate a VM or interact with the underlying OS; you only supply code and trigger conditions. Running a dedicated VM for a web application directly contradicts FaaS, as FaaS is designed for event-driven, stateless, short-lived workloads rather than a persistent hosted website.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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