The answer is Infrastructure as a Service (IaaS). This is the correct choice because IaaS provides virtual machines where you have full control over the operating system, including custom registry settings and specific Windows Server versions, while the cloud provider manages only the physical hardware. In contrast, Platform as a Service (PaaS) abstracts away the OS and runtime, making it impossible to apply unsupported custom configurations. On the Microsoft Azure Fundamentals AZ-900 exam, this scenario tests your ability to differentiate service models based on control versus management overhead—a common trap is assuming PaaS can handle any application, but it only supports standardized runtimes. Remember the memory tip: IaaS gives you the keys to the car (OS control), PaaS gives you a taxi (just run your code), and SaaS gives you a bus (ready-to-use software).
AZ-900 Describe cloud concepts Practice Question
This AZ-900 practice question tests your understanding of describe cloud concepts. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company is migrating a custom-built inventory management application to the cloud. The application runs on a specific version of Windows Server and requires custom registry settings that are not supported in a platform as a service (PaaS) offering. The company wants to avoid the overhead of managing physical servers but still needs full control over the operating system and application dependencies. Which cloud service model should the company use?
Correct. IaaS provides virtual machines with full control over the operating system, allowing custom registry settings and specific Windows Server versions.
B
Platform as a Service (PaaS)
Why wrong: Incorrect. PaaS abstracts the operating system and runtime, limiting control over OS-level configurations such as registry settings.
C
Software as a Service (SaaS)
Why wrong: Incorrect. SaaS delivers a fully managed application, offering no control over the underlying OS or infrastructure.
D
Function as a Service (FaaS)
Why wrong: Incorrect. FaaS (serverless) runs code in response to events without any control over the underlying operating system or environment.
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)
The company needs full control over the operating system and custom registry settings, which are not supported in PaaS. Infrastructure as a Service (IaaS) provides virtualized computing resources (e.g., virtual machines) where the customer manages the OS, applications, and dependencies, while the cloud provider handles the physical hardware. This model allows the company to run a specific version of Windows Server with custom registry configurations without managing physical servers.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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
Correct. IaaS provides virtual machines with full control over the operating system, allowing custom registry settings and specific Windows Server versions.
Related concept
Read the scenario before looking for a memorised answer.
✗
Platform as a Service (PaaS)
Why it's wrong here
Incorrect. PaaS abstracts the operating system and runtime, limiting control over OS-level configurations such as registry settings.
✗
Software as a Service (SaaS)
Why it's wrong here
Incorrect. SaaS delivers a fully managed application, offering no control over the underlying OS or infrastructure.
✗
Function as a Service (FaaS)
Why it's wrong here
Incorrect. FaaS (serverless) runs code in response to events without any control over the underlying operating system or environment.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may choose PaaS because it reduces management overhead, but they overlook the explicit requirement for custom registry settings and full OS control, which only IaaS can provide.
Detailed technical explanation
How to think about this question
IaaS provides virtual machines (VMs) via hypervisors like Hyper-V or KVM, where the customer has full administrative access to the guest OS (e.g., via RDP or SSH) and can modify registry keys (e.g., HKLM\SYSTEM\CurrentControlSet). In contrast, PaaS offerings like Azure App Service run in a sandboxed environment that restricts registry writes and OS-level changes, enforcing a shared responsibility model where the provider manages the OS. Real-world scenarios include migrating legacy line-of-business applications that require specific Windows Server features (e.g., Active Directory integration or COM+ components) that are incompatible with PaaS.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this AZ-900 question in full detail.
Describe cloud concepts — This question tests Describe cloud concepts — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Infrastructure as a Service (IaaS) — The company needs full control over the operating system and custom registry settings, which are not supported in PaaS. Infrastructure as a Service (IaaS) provides virtualized computing resources (e.g., virtual machines) where the customer manages the OS, applications, and dependencies, while the cloud provider handles the physical hardware. This model allows the company to run a specific version of Windows Server with custom registry configurations without managing physical servers.
What should I do if I get this AZ-900 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.