MS-900 Describe cloud concepts Practice Question
A development team wants to build a custom web application. They choose a cloud service that provides the runtime environment, operating system, and middleware, but the team is responsible for writing and deploying their own code. The provider automatically applies patches to the underlying infrastructure. Which cloud service model best describes this approach?
⚠ Common exam trap
A common mix-up: candidates confuse IaaS with PaaS because both involve deploying custom code, but IaaS requires the team to manage the OS and middleware patching, whereas PaaS automates that responsibility.
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) provides the runtime environment, operating system, and middleware, allowing developers to focus on writing and deploying their own code while the cloud provider manages the underlying infrastructure, including automatic patching. This model abstracts the hardware and OS layer, giving the team full control over application code but not the platform stack.
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) delivers raw compute, storage, and networking, but the customer is responsible for the operating system, runtime, web server, middleware, and all patching. To run a custom web application, the team would need to provision and continuously maintain VMs, install and update the application stack, and manage scalability and availability. This does not match the requirement of focusing on code deployment while the platform is managed, so it is incorrect.
- ✓
Platform as a Service (PaaS)
Why this is correct
Platform as a Service (PaaS) is correct because it provides a fully managed hosting environment that includes the operating system, language runtime, web server, and middleware, along with built-in deployment and scaling features. In a service like Azure App Service, the development team simply deploys its custom code and configuration, and the platform handles patching, load balancing, and high availability. This allows the team to focus on building the application rather than maintaining the underlying infrastructure.
- ✗
Software as a Service (SaaS)
Why it's wrong here
Software as a Service (SaaS) delivers a complete, ready-to-use application such as Microsoft 365 or Dynamics 365, where the vendor manages everything from the infrastructure to the application features. Customers can only configure or customize the software within pre-defined limits and cannot deploy or run their own custom code in that environment. Because the development team needs to build a new custom web application, SaaS is not the right model.
- ✗
Function as a Service (FaaS)
Why it's wrong here
Function as a Service (FaaS), such as Azure Functions, is an event-driven serverless compute model where you deploy individual, stateless functions that are executed in response to triggers. It does not offer a persistent application platform with middleware, routing, and session management that a full custom web application typically requires. While FaaS is useful for specific microservices and API endpoints, deploying a complete custom web application would require re-architecting the app into functions, so it is incorrect here.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This MS-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 MS-900 exam.