MS-900 Describe cloud concepts Practice Question
A company is evaluating moving its on-premises infrastructure to a cloud environment. They want a service that provides virtual machines, storage, and networking capabilities while retaining full control over the operating system and applications. Which cloud service model best meets this requirement?
⚠ Common exam trap
Test-takers frequently confuse Private Cloud (a deployment model) with a service model, mistakenly thinking it inherently provides full OS control, when in fact the level of control depends on whether IaaS, PaaS, or SaaS is used within that private cloud.
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)
Infrastructure as a Service (IaaS) provides virtualized computing resources, including virtual machines, storage, and networking, over the internet. The customer retains full administrative control over the operating system, applications, and middleware, while the cloud provider manages the underlying physical hardware. This matches the requirement for full OS and application control.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Software as a Service (SaaS)
Why it's wrong here
SaaS delivers complete, fully managed applications such as email or CRM over the Internet; customers configure only tenant-level settings and never control the operating system, server, or network. Moving on-premises infrastructure to SaaS would require replacing existing workloads with commercial applications, demanding business-process reengineering and data migration rather than a direct infrastructure transfer. Because SaaS abstracts away the infrastructure entirely, it cannot satisfy an evaluation focused on moving existing on-premises server environments.
- ✗
Platform as a Service (PaaS)
Why it's wrong here
PaaS provides a managed hosting platform—runtime environments, databases, middleware, and development tools—so users write and deploy code without managing VMs or guest operating systems. If the company moved to PaaS, it would have to refactor applications to run on platform services and would lose administrative control over infrastructure, making it unsuited for a scenario that is about relocating existing infrastructure rather than enabling application development. The provider handles patching and scaling, but that is precisely the responsibility the evaluation's infrastructure focus requires the customer to retain.
- ✓
Infrastructure as a Service (IaaS)
Why this is correct
IaaS offers virtualized compute, storage, and networking resources via services like Azure Virtual Machines, with the customer retaining control over the guest OS, applications, and middleware while the provider manages the physical datacenter. This service model supports a direct lift-and-shift migration of on-premises servers, including preservation of existing OS images and system configurations, with minimal re-architecture. Because the evaluation specifically targets moving infrastructure, IaaS is the correct choice as it gives the needed visibility and control over the entire computing stack.
- ✗
Private Cloud
Why it's wrong here
Private cloud is a deployment model, not a service model; a private cloud can be built on IaaS, run PaaS workloads, or deliver SaaS applications within a single-tenant, dedicated environment. Describing a move as 'private cloud' indicates exclusivity and isolation of resources but does not define whether the organization will manage VMs, use a platform, or consume applications. For an infrastructure-focused migration, private cloud is insufficiently precise because it does not specify the abstraction level of the underlying service, which is the actual decision being made.
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