AZ-900 Describe Azure architecture and services Practice Question
A company is migrating its on-premises batch processing jobs to Azure. The jobs are triggered by file uploads to an on-premises file share. After migration, the files will be uploaded to Azure Blob Storage. The company wants a solution where code runs automatically whenever a new blob is created, with no requirement to manage servers or containers. The code must process the blob and then terminate. Compute resources should be used only when there is a file to process. Which Azure compute service should the company use?
⚠ Common exam trap
Watch out — candidates often choose Azure App Service (Option A) because they associate it with running code automatically, but fail to recognize that App Service runs continuously and is not designed for event-driven, ephemeral tasks that terminate after processing a single blob.
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
✓
Azure Functions
Azure Functions is the correct choice because it provides a serverless compute service that can be triggered automatically by Azure Blob Storage events (e.g., new blob creation). The code runs only when a blob is uploaded, processes it, and then terminates, ensuring zero compute cost when idle. No servers or containers need to be managed, aligning perfectly with the requirement for event-driven, ephemeral execution.
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 App Service
Why it's wrong here
Azure App Service is a platform-as-a-service (PaaS) for hosting web apps, REST APIs, and mobile back ends. It runs continuously and is not designed for event-triggered, short-lived executions that automatically start and stop. It also requires an always-on instance, meaning you pay for running the app even when idle.
When this WOULD be correct
A company needs to host a web API that handles HTTP requests from clients, with built-in scaling and load balancing, but does not require event-driven blob processing or automatic termination after each request.
- ✗
Azure Kubernetes Service (AKS)
Why it's wrong here
AKS is a managed container orchestration service that requires managing a cluster of virtual machines (nodes). While you can run event-driven workloads on AKS using tools like Keda, it involves more operational overhead than a serverless option and does not naturally scale to zero when idle.
When this WOULD be correct
A company needs to run containerized batch processing jobs that require orchestration, scaling, and management of multiple containers, and is willing to manage the underlying cluster or use a managed Kubernetes service.
- ✓
Azure Functions
Why this is correct
Azure Functions is a serverless compute service that runs code in response to events (e.g., blob creation, HTTP requests, queues) and automatically scales. It charges only for execution time, eliminating idle cost. This matches the need for automatic, triggered processing with no infrastructure management.
- ✗
Azure Virtual Machine Scale Sets
Why it's wrong here
Azure Virtual Machine Scale Sets provide a group of load-balanced VMs that can autoscale. However, they require you to manage VMs, install the application code, and handle patching. They incur costs for idle VMs and are not an event-driven serverless compute service.
When this WOULD be correct
A company needs to run a custom application that processes large batches of files on a schedule, requiring full control over the OS and the ability to scale out to hundreds of VMs automatically based on load, with no need for event-driven triggers.
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.
✓Azure FunctionsCorrect answer▾
Why this is correct
Azure Functions is a serverless compute service that runs code in response to events (e.g., blob creation, HTTP requests, queues) and automatically scales. It charges only for execution time, eliminating idle cost. This matches the need for automatic, triggered processing with no infrastructure management.
✗Azure App ServiceWrong answer — click to see why▾
Why this is wrong here
Azure App Service runs web applications continuously, not event-driven, and requires always-on resources; it does not terminate after processing a blob, nor does it automatically trigger on blob creation without additional configuration like WebJobs.
★ When this WOULD be the correct answer
A company needs to host a web API that handles HTTP requests from clients, with built-in scaling and load balancing, but does not require event-driven blob processing or automatic termination after each request.
Why candidates choose this
Candidates may confuse App Service's ability to run background tasks (via WebJobs) with the serverless, event-driven model of Azure Functions, overlooking that Functions are purpose-built for such scenarios.
✗Azure Kubernetes Service (AKS)Wrong answer — click to see why▾
Why this is wrong here
Azure Kubernetes Service (AKS) requires managing a cluster of VMs and containers, which contradicts the requirement to not manage servers or containers and to use compute resources only when processing files.
★ When this WOULD be the correct answer
A company needs to run containerized batch processing jobs that require orchestration, scaling, and management of multiple containers, and is willing to manage the underlying cluster or use a managed Kubernetes service.
Why candidates choose this
Candidates may think AKS is suitable for event-driven batch processing because it can run containers triggered by events, but they overlook the requirement to avoid managing servers or containers.
✗Azure Virtual Machine Scale SetsWrong answer — click to see why▾
Why this is wrong here
Azure Virtual Machine Scale Sets require managing VMs and do not automatically terminate after processing a blob; they are designed for scaling pre-configured VMs, not event-driven serverless execution.
★ When this WOULD be the correct answer
A company needs to run a custom application that processes large batches of files on a schedule, requiring full control over the OS and the ability to scale out to hundreds of VMs automatically based on load, with no need for event-driven triggers.
Why candidates choose this
Candidates may think scale sets can automatically run code on blob creation because they support autoscaling, but they lack native event-driven triggers and serverless execution model.
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?”
Quick reference
Azure Blob Storage Tier Comparison
| Tier | Storage Cost | Retrieval Cost | Latency | Use Case |
|---|---|---|---|---|
| Hot | Highest | Lowest | Immediate | Active data, frequent reads |
| Cool | Lower | Higher | Immediate | Data accessed < once / month |
| Cold | Lower still | Higher | Immediate | Data accessed < once / quarter |
| Archive | Lowest | Highest + rehydration delay | Hours | Long-term compliance retention |
Go deeper
Related to this question
Learn chapter
Azure Regions and Geographies
Key term
Blob
A blob is a large piece of unstructured data, like a photo or video, stored in the cloud with a unique identifier.
Key term
Blob storage
Blob storage is a cloud service for storing large amounts of unstructured data, such as text or binary data, like documents, images, and videos.
About these practice questions
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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.