MS-900 Describe cloud concepts Practice Question
A cloud provider offers virtual machines, but customers must install, configure, and maintain the operating system and applications. Which cloud service model does this describe?
⚠ Common exam trap
Candidates often confuse IaaS with PaaS because both involve virtual machines, but PaaS (e.g., Azure App Service) hides the OS and runtime, whereas IaaS requires full customer OS management.
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
✓
IaaS (Infrastructure as a Service)
This scenario describes Infrastructure as a Service (IaaS), where the cloud provider supplies virtualized computing resources such as virtual machines, storage, and networking, but the customer retains full control over the operating system, middleware, and applications. In IaaS, the provider manages only the physical infrastructure (hypervisor, servers, storage, and network), while the customer is responsible for OS installation, configuration, patching, and application management. This aligns directly with the question's description of customer-managed OS and applications on provider-hosted VMs.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
IaaS (Infrastructure as a Service)
Why this is correct
In IaaS, the provider supplies virtualized compute, storage, and networking as on-demand resources, but the customer deploys and manages the virtual machines' guest OS, runtime, and installed applications. This shared-responsibility model places patching, configuration, and application stack maintenance squarely on the customer, which is exactly the scenario described. The provider's responsibility ends at the hypervisor and physical infrastructure, so customers must handle everything inside the VM.
- ✗
PaaS (Platform as a Service)
Why it's wrong here
PaaS (e.g., Azure App Service) abstracts the OS and runtime entirely; the provider manages the underlying VMs, middleware, and operating system, and the customer simply deploys code or containers. Unlike IaaS, there are no customer-managed VMs or guest OS updates to apply, so the described requirement to manage the OS rules out PaaS as the correct classification.
- ✗
SaaS (Software as a Service)
Why it's wrong here
SaaS delivers a fully functional application through a browser or API, and the provider owns all underlying components—servers, OS, runtime, and the application itself. Customers configure settings and manage their own data but never touch a VM or an operating system, so the scenario of being handed virtual machines with OS-level responsibility cannot be SaaS.
- ✗
FaaS (Function as a Service)
Why it's wrong here
FaaS (serverless functions) runs individual units of code in response to events, with the platform automatically provisioning and scaling compute resources, yet the customer never sees a VM or manages an OS. In the described model, where VMs are the offered unit and the customer must own the OS and applications, the architecture is far more granular than FaaS's event-driven, fully abstracted execution.
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