AZ-900 Describe cloud concepts Practice Question
A small business wants to move its accounting software to the cloud to avoid purchasing and maintaining physical servers. Which cloud service model would provide the accounting application as a ready-to-use service over the internet?
⚠ Common exam trap
It's easy for candidates to confuse IaaS with SaaS because both involve 'servers in the cloud,' but IaaS still requires the customer to manage the operating system and application software, while SaaS delivers a fully managed application.
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
✓
Software as a Service (SaaS)
(SaaS) is correct because the business needs a ready-to-use accounting application delivered over the internet without managing underlying infrastructure. SaaS provides fully functional software accessed via a web browser, where the provider handles all maintenance, updates, and server management, aligning perfectly with the goal of avoiding physical server ownership.
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 it's wrong here
IaaS provides virtualized computing resources such as virtual machines, storage, and networking on demand, but it does not include a ready-made accounting application. The customer remains responsible for deploying and managing the entire software stack, including the operating system, middleware, and the accounting software itself, which still requires purchasing a license. Thus, IaaS only avoids the capital cost of physical servers, not the software purchase.
When this WOULD be correct
A company wants to migrate its on-premises servers to the cloud to run custom accounting software, avoiding hardware maintenance but retaining control over the OS and applications. IaaS would provide the virtual servers and storage needed.
- ✗
Platform as a Service (PaaS)
Why it's wrong here
PaaS offers a managed development and hosting environment with tools for building, testing, and deploying custom applications, but it does not furnish end-user business software. To use accounting functionality on PaaS, an organization must either develop its own application or acquire and deploy a third-party package onto the platform, which still involves a purchasing or development effort. PaaS enables custom solutions rather than providing an instant, ready-to-run accounting package.
When this WOULD be correct
A developer wants to build a custom web application without managing the underlying OS, runtime, or middleware. PaaS would provide the development and deployment platform, while the developer codes the application.
- ✓
Software as a Service (SaaS)
Why this is correct
SaaS is a cloud service model that delivers complete, ready-to-use applications over the internet, typically on a subscription basis. For accounting, a SaaS provider like QuickBooks Online or Microsoft Dynamics 365 supplies the fully functional software, including the application, data storage, and underlying infrastructure, eliminating the need to purchase perpetual licenses or install software on local machines. The customer just configures the service and begins using it.
- ✗
Function as a Service (FaaS)
Why it's wrong here
FaaS is an event-driven serverless execution model where individual functions or code snippets run in response to triggers, abstracting away infrastructure management. It is designed for microservices and integrations, not for delivering a complete, user-facing application such as accounting software; using FaaS for accounting would require writing and maintaining all of the application's business logic and data processing code. Therefore, FaaS does not help avoid the cost or effort of sourcing the accounting software itself.
When this WOULD be correct
A company wants to run custom code for processing financial transactions without managing servers, triggered by events like new invoices. FaaS would be correct because it allows deploying individual functions that scale automatically and charge per execution.
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.
✓Software as a Service (SaaS)Correct answer▾
Why this is correct
SaaS is a cloud service model that delivers complete, ready-to-use applications over the internet, typically on a subscription basis. For accounting, a SaaS provider like QuickBooks Online or Microsoft Dynamics 365 supplies the fully functional software, including the application, data storage, and underlying infrastructure, eliminating the need to purchase perpetual licenses or install software on local machines. The customer just configures the service and begins using it.
✗Infrastructure as a Service (IaaS)Wrong answer — click to see why▾
Why this is wrong here
IaaS provides virtualized computing resources like virtual machines and storage, not ready-to-use accounting software. The business needs a fully managed application, not infrastructure to deploy and manage themselves.
★ When this WOULD be the correct answer
A company wants to migrate its on-premises servers to the cloud to run custom accounting software, avoiding hardware maintenance but retaining control over the OS and applications. IaaS would provide the virtual servers and storage needed.
Why candidates choose this
Candidates may confuse cloud service models, thinking that moving to the cloud always means using IaaS, or they may not distinguish between providing infrastructure versus providing a complete application.
✗Platform as a Service (PaaS)Wrong answer — click to see why▾
Why this is wrong here
PaaS provides a platform to develop, run, and manage applications, but the customer still builds or deploys the application. The question specifies the accounting software is a ready-to-use service, which is SaaS.
★ When this WOULD be the correct answer
A developer wants to build a custom web application without managing the underlying OS, runtime, or middleware. PaaS would provide the development and deployment platform, while the developer codes the application.
Why candidates choose this
Candidates may confuse PaaS with SaaS because both involve cloud-hosted services, but PaaS requires the user to deploy their own application, not use a pre-built one.
✗Function as a Service (FaaS)Wrong answer — click to see why▾
Why this is wrong here
FaaS (Function as a Service) provides a platform for running individual functions in response to events, not a complete ready-to-use accounting application. The question specifies a need for a full application delivered over the internet, which is SaaS.
★ When this WOULD be the correct answer
A company wants to run custom code for processing financial transactions without managing servers, triggered by events like new invoices. FaaS would be correct because it allows deploying individual functions that scale automatically and charge per execution.
Why candidates choose this
Candidates may confuse FaaS with SaaS because both are cloud services, or they might think 'function' refers to application functionality, not realizing FaaS is for event-driven code execution rather than full applications.
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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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.