AZ-900 Describe cloud concepts Practice Question
A company is developing a custom web application that will be deployed to Azure. The development team wants to minimize operational overhead and avoid any responsibility for managing the underlying operating system, runtime, or middleware. They want to focus solely on writing application code and managing data. Which cloud service model should the company use for this application?
⚠ Common exam trap
A common mix-up: candidates confuse PaaS with IaaS because they think 'custom application' requires full control over the OS, but the question explicitly states the team wants to avoid managing the OS, runtime, or middleware, which is the defining characteristic of PaaS.
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 abstracts the underlying OS, runtime, and middleware, allowing developers to focus solely on writing application code and managing data. Azure App Service is a PaaS offering that provides automatic patching, load balancing, and scaling without any responsibility for the host OS or runtime environment. This directly matches the requirement to minimize operational overhead and avoid managing infrastructure layers.
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
Infrastructure as a Service (IaaS) is incorrect because it supplies raw compute, storage, and networking resources, typically as virtual machines. The customer remains responsible for provisioning and maintaining the OS, runtime, middleware, and application stack, including patches and scaling of the VM fleet. That operational burden contradicts the stated requirement to avoid managing infrastructure, making PaaS the more appropriate choice for this team.
When this WOULD be correct
A company needs to migrate an existing on-premises application to Azure with minimal changes, requiring full control over the OS and middleware for compatibility. They are willing to manage the OS and runtime to avoid re-architecting the application.
- ✓
Platform as a Service (PaaS)
Why this is correct
Platform as a Service (PaaS) is the correct model because it delivers a managed hosting environment—such as Azure App Service—that abstracts the underlying OS, runtime, and infrastructure. The development team can deploy custom web application code and manage application-level data without provisioning or patching VMs. This directly aligns with the requirement to avoid infrastructure overhead while retaining full control over the application's code and data.
- ✗
Software as a Service (SaaS)
Why it's wrong here
Software as a Service (SaaS) is incorrect because it provides a fully finished application—like Office 365 or Salesforce—that is already configured and ready for end users. The customer does not write or deploy custom application code, nor do they manage the underlying platform or data schema in the way a custom web application requires. Since the scenario demands developing and hosting a custom application, SaaS would not offer the necessary development or deployment flexibility.
When this WOULD be correct
A company needs to use a cloud-based email service like Microsoft 365 without managing servers or software. The question would ask for a model where the provider manages everything, and users only use the application.
- ✗
Functions as a Service (FaaS)
Why it's wrong here
FaaS (e.g., Azure Functions) is serverless and event-driven. While it reduces infrastructure management, it is optimized for individual functions or microservices, not for hosting a full custom web application with persistent code and data management. PaaS is the appropriate model for this scenario.
When this WOULD be correct
A company needs to execute code in response to events (e.g., file uploads, database changes) without provisioning or managing servers, and the code is stateless and short-lived. The team wants to pay only for execution time and avoid idle costs.
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
Platform as a Service (PaaS) is the correct model because it delivers a managed hosting environment—such as Azure App Service—that abstracts the underlying OS, runtime, and infrastructure. The development team can deploy custom web application code and manage application-level data without provisioning or patching VMs. This directly aligns with the requirement to avoid infrastructure overhead while retaining full control over the application's code and data.
✗Infrastructure as a Service (IaaS)Wrong answer — click to see why▾
Why this is wrong here
IaaS provides virtualized computing resources like VMs and storage, but the customer is responsible for managing the OS, runtime, and middleware. The question specifies the team wants to avoid managing the underlying OS, runtime, or middleware, which contradicts IaaS.
★ When this WOULD be the correct answer
A company needs to migrate an existing on-premises application to Azure with minimal changes, requiring full control over the OS and middleware for compatibility. They are willing to manage the OS and runtime to avoid re-architecting the application.
Why candidates choose this
Candidates may think IaaS is the default for custom applications, or they confuse 'custom' with needing full control, not realizing PaaS offers the same custom development without infrastructure management.
✗Software as a Service (SaaS)Wrong answer — click to see why▾
Why this is wrong here
SaaS provides a fully managed application, not a platform for custom development. The question specifies the team wants to write custom code and manage data, which is not possible with SaaS as it offers ready-to-use software.
★ When this WOULD be the correct answer
A company needs to use a cloud-based email service like Microsoft 365 without managing servers or software. The question would ask for a model where the provider manages everything, and users only use the application.
Why candidates choose this
Candidates may confuse 'minimal operational overhead' with SaaS, but SaaS eliminates all management including code, whereas the team wants to write code.
✗Functions as a Service (FaaS)Wrong answer — click to see why▾
Why this is wrong here
FaaS (Functions as a Service) is a subset of serverless computing that runs individual functions in response to events, but it still requires managing application code and data. The question specifies minimizing operational overhead and avoiding management of runtime/middleware, which PaaS fully provides, while FaaS introduces additional complexity around function orchestration and state management.
★ When this WOULD be the correct answer
A company needs to execute code in response to events (e.g., file uploads, database changes) without provisioning or managing servers, and the code is stateless and short-lived. The team wants to pay only for execution time and avoid idle costs.
Why candidates choose this
Candidates may confuse FaaS with PaaS because both abstract infrastructure, but FaaS is event-driven and granular, not a full platform for web applications. The desire to 'focus solely on writing code' might lead them to choose FaaS, overlooking that PaaS is more appropriate for a complete web app.
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
What is Cloud Computing?
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
Azure App Service
Azure App Service is a fully managed platform for building, deploying, and scaling web applications and APIs without managing the underlying infrastructure.
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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.