AZ-900 Describe Azure architecture and services Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✓

  Azure Virtual Machines: Provides full control over the operating system and allows custom software installations

  Why this is correct

  Azure Virtual Machines is an Infrastructure-as-a-Service (IaaS) offering that provides a dedicated VM with full administrative access, including the ability to install custom software, modify OS settings, apply kernel patches, and manage configurations. Because the customer controls the guest OS, it is ideal for legacy applications, custom workloads, or software that requires specific system libraries, drivers, or performance tuning. Microsoft only manages the underlying physical infrastructure; you are responsible for the OS lifecycle and everything installed on it.

• ✓

  Azure App Service: A platform for building and hosting web apps, RESTful APIs, and mobile backends

  Why this is correct

  Azure App Service is a Platform-as-a-Service (PaaS) compute solution that abstracts the underlying web server and operating system, letting developers deploy web applications, RESTful APIs, and mobile backends without provisioning VMs or patching the OS. It automatically handles load balancing, TLS certificates, autoscaling, and built-in authentication so you can focus on application code. The trade-off is reduced control: you cannot access or modify the underlying virtual machine hosting your app.

• ✓

  Azure Functions: Enables event-driven code execution without managing infrastructure

  Why this is correct

  Azure Functions is a serverless compute service where code runs in response to triggers such as HTTP requests, queue messages, or timer schedules, with no need to provision or manage infrastructure. The platform dynamically allocates resources, scales from zero to meet demand, and bills only for execution time and resources consumed. This event-driven model is best for short-lived, stateless workloads, and it requires attention to execution timeouts, cold starts, and concurrency limits.

• ✗

  Azure Virtual Machines: A serverless compute service for running code on demand

  Why it's wrong here

  Describing Azure Virtual Machines as a serverless compute service for running code on demand is incorrect because VMs are IaaS with persistent, always-on capacity that you must size, patch, and scale manually. Serverless is typified by Azure Functions, which executes event-driven code on scaled-out infrastructure that you never see or manage. In an Azure VM, you have a fixed or configured virtual hardware footprint that runs whether or not your code is actively executing, so billing differs from pay-per-execution.

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  Azure App Service: Provides full control over the virtual machine including OS updates

  Why it's wrong here

  This statement is wrong because Azure App Service is a PaaS offering where Microsoft fully manages the underlying OS and applies security updates, leaving you no direct control over the virtual machine. Full control over the OS and updates is the domain of Azure Virtual Machines (IaaS), where you can manage system settings and install custom software. App Service does provide configuration at the application level and supports deployment slots, but it does not expose guest OS access.

• ✗

  Azure Functions: A fully managed platform for building web applications

  Why it's wrong here

  Azure Functions is not a fully managed platform for building web applications; that description matches Azure App Service, which is purpose-built for hosting websites, RESTful APIs, and mobile backends with integrated scaling, CI/CD, and deployment slots. Azure Functions is instead an event-driven serverless compute service that runs discrete pieces of code in response to triggers, even though HTTP triggers can expose lightweight API endpoints. A full web framework with routing, middleware, and persistent request handling is generally better served by App Service than by Functions.

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