Question 176 of 981
AZ-900 Describe Azure architecture and services Practice Question
A company develops a data processing application that runs only when new files are uploaded to an Azure Blob Storage container. The application must scale automatically to handle hundreds of simultaneous file uploads and must not incur cost when no files are being processed. The development team wants the simplest solution that requires no infrastructure management. Which Azure compute service should they use?
⚠ Common exam trap
It's easy for candidates to confuse Azure Functions with Azure Batch, thinking both are serverless, but Azure Batch requires explicit job and pool management, making it unsuitable for simple event-driven, per-file processing with zero idle cost.
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 with a Blob Storage trigger
Azure Functions with a Blob Storage trigger is the correct choice because it provides an event-driven, serverless compute model that automatically scales to handle hundreds of concurrent file uploads without requiring any infrastructure management. The function executes only when a new blob is created in the container, ensuring zero cost when no files are being processed, and the platform handles scaling out to meet demand.
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 Scale Set with autoscale rules
Why it's wrong here
A Virtual Machine Scale Set requires you to manage virtual machine images, operating system updates, and scaling rules. It incurs cost even when idle because the underlying VMs are running. While it can scale automatically, it is not a serverless or simplest solution for event-driven file processing.
When this WOULD be correct
A question requiring a custom Windows/Linux environment with full control over the OS, specific software installations, and the need to scale based on CPU/memory metrics, not event-driven triggers. For example, a legacy application that must run on a specific OS version and scale based on load.
- ✗
Azure Batch
Why it's wrong here
Azure Batch is designed for large-scale parallel and high-performance computing jobs. It requires you to create and manage a pool of compute nodes. It is overkill for simple event-driven blob processing and introduces management overhead that the team wants to avoid.
When this WOULD be correct
A company needs to run a high-throughput, parallel batch processing job (e.g., rendering thousands of video frames or processing large datasets) on a scheduled basis or when a large batch of data is available, and they require control over job orchestration and scaling.
- ✓
Azure Functions with a Blob Storage trigger
Why this is correct
Azure Functions is serverless, scales automatically in response to events, and charges only for execution time. Using a Blob Storage trigger, the function runs whenever a new blob is created. This is the simplest solution that meets all requirements: automatic scaling, no cost when idle, and no infrastructure management.
- ✗
Azure Container Instances
Why it's wrong here
Azure Container Instances allow you to run containers without managing servers. However, they are not inherently event-driven like Azure Functions. To trigger a container instance on a blob upload, you would need additional components such as Azure Logic Apps or an Azure Function, increasing complexity. Also, while you can stop containers to save cost, the default model costs for the container's lifetime.
When this WOULD be correct
A company needs to run a containerized application that processes files in batches, requires custom libraries or dependencies not supported by Azure Functions, and needs to run for longer than the maximum execution time of Azure Functions (e.g., over 10 minutes). The simplest solution with no infrastructure management for container orchestration would be Azure Container Instances.
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 Functions with a Blob Storage triggerCorrect answer▾
Why this is correct
Azure Functions is serverless, scales automatically in response to events, and charges only for execution time. Using a Blob Storage trigger, the function runs whenever a new blob is created. This is the simplest solution that meets all requirements: automatic scaling, no cost when idle, and no infrastructure management.
✗Azure Virtual Machines Scale Set with autoscale rulesWrong answer — click to see why▾
Why this is wrong here
Azure Virtual Machines Scale Set requires managing VMs and incurs cost even when idle, failing the 'no cost when no files are processed' requirement. It also involves more infrastructure management than the simplest solution.
★ When this WOULD be the correct answer
A question requiring a custom Windows/Linux environment with full control over the OS, specific software installations, and the need to scale based on CPU/memory metrics, not event-driven triggers. For example, a legacy application that must run on a specific OS version and scale based on load.
Why candidates choose this
Candidates may think autoscaling VMs is the only way to handle hundreds of uploads, overlooking serverless options. They might also be unfamiliar with Azure Functions' event-driven scaling and cost model.
✗Azure BatchWrong answer — click to see why▾
Why this is wrong here
Azure Batch is designed for large-scale parallel batch computing jobs, not for event-driven, serverless execution triggered by file uploads. It requires managing job schedules and pools, adding complexity and cost when idle.
★ When this WOULD be the correct answer
A company needs to run a high-throughput, parallel batch processing job (e.g., rendering thousands of video frames or processing large datasets) on a scheduled basis or when a large batch of data is available, and they require control over job orchestration and scaling.
Why candidates choose this
Candidates may associate Batch with automated scaling and processing of files, overlooking that it is not event-triggered and requires infrastructure management, unlike the serverless Functions trigger.
✗Azure Container InstancesWrong answer — click to see why▾
Why this is wrong here
Azure Container Instances requires manual scaling or integration with other services for auto-scaling, and it incurs cost even when idle if containers are running. It also involves more infrastructure management than Azure Functions.
★ When this WOULD be the correct answer
A company needs to run a containerized application that processes files in batches, requires custom libraries or dependencies not supported by Azure Functions, and needs to run for longer than the maximum execution time of Azure Functions (e.g., over 10 minutes). The simplest solution with no infrastructure management for container orchestration would be Azure Container Instances.
Why candidates choose this
Candidates may think container instances are serverless and automatically scale, but they confuse container instances with serverless functions, overlooking that Azure Functions is the simpler, event-driven, cost-effective choice for this specific blob-triggered workload.
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 |
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Last reviewed: Jun 11, 2026
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.
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