AZ-900 Describe cloud concepts 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.

• ✓

  Infrastructure as a Service (IaaS)

  Why this is correct

  IaaS delivers virtualized compute, storage, and networking resources on demand, with the cloud provider managing only the physical data center and hypervisor layer. The customer retains full administrative control over the guest OS, file systems, and installed applications, which is exactly what is needed when migrating an existing workload without rewriting it. This shared responsibility model makes IaaS the closest to a traditional data center while eliminating hardware procurement and maintenance. For an existing application that requires OS-level customization, IaaS is the appropriate choice.

• ✗

  Platform as a Service (PaaS)

  Why it's wrong here

  PaaS abstracts away the underlying OS and runtime environment, automatically managing patching, scaling, and middleware components such as application servers or database engines. While this reduces operational overhead, the customer loses the ability to configure the operating system or install custom binaries, which may break or require re-platforming an existing application. For a migration of an existing workload that expects tight OS-level control, PaaS is not the right choice because of the provider-managed runtime and platform constraints.

  When this WOULD be correct

  A company wants to deploy a web application using a built-in runtime (e.g., Node.js, .NET) without managing the OS or patches, focusing only on code and data. PaaS would be correct.

• ✗

  Software as a Service (SaaS)

  Why it's wrong here

  SaaS provides a complete, ready-to-use application accessed over the internet, where the vendor manages every part of the stack, from the OS and network to the application itself. The customer only configures user settings and data, with no capability to alter the underlying execution environment or install custom code. This is unsuitable for migrating an existing application that requires custom runtime or infrastructure control, because SaaS offers only application-level configurability, not infrastructure or OS access.

  When this WOULD be correct

  A company needs to use a customer relationship management (CRM) application without managing any infrastructure or software updates, and wants to pay a subscription fee for access. In this scenario, SaaS is the correct choice.

• ✗

  On-premises deployment

  Why it's wrong here

  On-premises deployment would require purchasing, cabling, and maintaining physical servers, alongside managing power, cooling, and hardware refreshes—the very capital expenditure and operational burden the company wants to eliminate. Although it offers the highest level of control, it does not provide the scalability or pay-as-you-go flexibility of cloud infrastructure, making it counterproductive for this migration scenario. The goal is to avoid physical hardware management, and on-premises directly contradicts that.

  When this WOULD be correct

  An exam scenario where the company must maintain full control over all hardware, software, and data due to strict regulatory compliance or security policies, and is willing to manage physical infrastructure.

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?”

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