Understanding Cloud Service Models: IaaS, PaaS, SaaS
A startup wants to run a web application without purchasing or managing any servers. They only want to upload their code and let the cloud provider handle everything from the runtime to scaling. Which cloud service model best fits this requirement?
Quick Answer
The answer is Platform as a Service (PaaS). This is the correct choice because PaaS abstracts away the underlying infrastructure, providing a fully managed hosting environment where you simply upload your code and the cloud provider handles the runtime, operating system, scaling, and load balancing—exactly what a startup needs to avoid purchasing or managing servers. On the Microsoft Azure Fundamentals AZ-900 exam, this scenario tests your ability to distinguish between the three cloud service models: IaaS gives you virtual machines to manage, SaaS delivers ready-to-use software, and PaaS sits in the middle as a platform for developers. A common trap is confusing PaaS with IaaS, but remember that if you don’t have to manage the OS or runtime, it’s PaaS. For a memory tip, think of PaaS as “Platform as a Service” where you bring your code and the platform does the rest—like Azure App Service, which handles automatic scaling and patching so you can focus purely on development.
⚠ Common exam trap
Many exam-takers confuse FaaS with PaaS because both are serverless, but FaaS is for individual functions triggered by events, not for hosting a complete web application with a persistent runtime.
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
✓
Platform as a Service (PaaS)
Platform as a Service (PaaS) is the correct model because it provides a fully managed hosting environment where the startup can deploy their web application code without needing to provision or manage underlying servers, operating systems, or runtime infrastructure. Azure App Service is a prime example of PaaS that handles automatic scaling, load balancing, and patching, allowing developers to focus solely on code.
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 virtual machines, storage and networking, leaving OS patching, runtime installation and scaling configuration to the startup. It tempts because it removes hardware procurement, but that fits lift-and-shift migrations needing full OS control, not code-only deployment with provider-managed runtime and scaling.
When this WOULD be correct
A question where the requirement is to have full control over the operating system and middleware, such as migrating an on-premises application to the cloud with minimal changes, and the customer is responsible for managing the runtime and scaling.
- ✓
Platform as a Service (PaaS)
Why this is correct
PaaS delivers a managed runtime where the provider patches the OS, middleware and scaling, so the startup uploads code only. This satisfies the stem's constraint of no server purchasing or management, unlike IaaS, which still leaves patching and capacity to the customer.
- ✗
Software as a Service (SaaS)
Why it's wrong here
SaaS delivers finished applications the customer merely consumes; the startup cannot upload its own web application code into it. It tempts because SaaS removes all server and runtime management, but that fits buying productivity software such as Microsoft 365, not deploying custom code.
- ✗
Function as a Service (FaaS)
Why it's wrong here
FaaS runs event-triggered functions, not a continuously listening web application with its own runtime and scaling configuration. It tempts because it is serverless and code-only, but that fits discrete event handlers, whereas the stem describes hosting a full web app, which PaaS covers.
When this WOULD be correct
A question that asks for a serverless compute service where you only upload individual functions (e.g., processing an image upload) and pay per execution, with no concern for the underlying runtime or scaling, would make FaaS correct.
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.
✓Platform as a Service (PaaS)Correct answer▾
Why this is correct
PaaS delivers a managed runtime where the provider patches the OS, middleware and scaling, so the startup uploads code only. This satisfies the stem's constraint of no server purchasing or management, unlike IaaS, which still leaves patching and capacity to the customer.
✗Infrastructure as a Service (IaaS)Wrong answer — click to see why▾
Why this is wrong here
IaaS provides virtualized servers and storage, but the startup would still need to manage the operating system, runtime, and scaling, which contradicts the requirement to avoid any server management.
★ When this WOULD be the correct answer
A question where the requirement is to have full control over the operating system and middleware, such as migrating an on-premises application to the cloud with minimal changes, and the customer is responsible for managing the runtime and scaling.
Why candidates choose this
Candidates may confuse IaaS with PaaS, thinking that IaaS also abstracts server management, but IaaS still requires the user to handle the OS and application stack.
✗Function as a Service (FaaS)Wrong answer — click to see why▾
Why this is wrong here
FaaS (Function as a Service) requires code to be deployed as individual functions triggered by events, not as a full web application. The startup wants to upload their entire web application code and let the cloud handle runtime and scaling, which is PaaS, not FaaS.
★ When this WOULD be the correct answer
A question that asks for a serverless compute service where you only upload individual functions (e.g., processing an image upload) and pay per execution, with no concern for the underlying runtime or scaling, would make FaaS correct.
Why candidates choose this
Candidates may confuse 'no server management' with serverless computing (FaaS), but FaaS is event-driven and not designed for hosting a complete web application with persistent state.
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?”
Go deeper
Related to this question
Learn chapter
IaaS, PaaS, and SaaS Explained
Key term
PaaS
Platform as a Service (PaaS) is a cloud computing model that provides a managed platform for developers to build, run, and manage applications without dealing with the underlying infrastructure.
Key term
Environment
An environment is a dedicated set of computing resources, configurations, and services used to develop, test, or host software applications in a controlled and repeatable way.
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Same concept, more angles
1 more way this is tested on AZ-900
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A startup wants to run a web application without managing the underlying servers. They only want to upload their code and let the cloud provider handle the runtime, scaling, and maintenance. Which cloud service model is this?
easy- ✓ A.Platform as a Service (PaaS)
- B.Infrastructure as a Service (IaaS)
- C.Software as a Service (SaaS)
- D.Function as a Service (FaaS)
Why A: Platform as a Service (PaaS) is the correct model because it provides a managed hosting environment where the startup can deploy their web application code without managing the underlying servers, operating systems, or runtime infrastructure. Azure App Service is a prime example of PaaS, handling automatic scaling, patching, and load balancing while the customer only focuses on code and data.
JA
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.