AZ-204 Practice Question: Event Grid trigger to replace Blob Storage…
Images are uploaded to a high-volume Blob Storage account. An Azure Function with a Blob Storage trigger processes each new image. The team has observed processing delays of up to 10 minutes on accounts with large numbers of containers and blobs. They need processing to start within seconds of upload. What should the developer change?
⚠ Common exam trap
Watch out — candidates often assume upgrading the hosting plan (Premium) will fix latency issues, but the root cause is the polling-based Blob Storage trigger, not the underlying infrastructure; the correct solution is to switch to an event-driven trigger like Event Grid.
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
✓
Replace the Blob Storage trigger with an Event Grid trigger and create a Blob Created event subscription that targets the Function's endpoint
Event Grid provides near-real-time event delivery (typically under 1 second) for Blob Created events, eliminating the polling latency inherent in the Blob Storage trigger. The Blob Storage trigger polls Azure Storage logs for new blobs, which can cause delays of up to 10 minutes in high-volume accounts with many containers and blobs. By switching to an Event Grid trigger, the function is invoked directly via HTTP webhook as soon as the blob is created, meeting the requirement for processing to start within seconds.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Replace the Blob Storage trigger with an Event Grid trigger and create a Blob Created event subscription that targets the Function's endpoint
Why this is correct
Event Grid delivers blob creation events within seconds of the upload by pushing events rather than polling. The Function receives the event payload (which includes the blob URI) and begins processing immediately. This eliminates the polling delay inherent in the Blob Storage trigger on large accounts.
- ✗
Switch to a Timer trigger that runs every 30 seconds and lists newly created blobs via the SDK
Why it's wrong here
A Timer trigger polling every 30 seconds cannot guarantee processing within seconds of upload because it introduces a fixed latency window of up to 30 seconds before the SDK lists newly created blobs. This approach is tempting because it avoids Blob Storage trigger scaling delays on accounts with many containers, and would be correct for scenarios where near-real-time latency is acceptable and the trigger’s event-driven behaviour is unreliable.
- ✗
Use a Queue Storage trigger and write blob metadata to the queue from the upload client
Why it's wrong here
This approach requires modifying the upload client to write queue messages, adding a dependency between the uploader and the processing pipeline. Event Grid decouples the producer (blob upload) from the consumer (Function) without requiring changes to the upload side.
- ✗
Move the Function to a Premium plan, which uses a dedicated worker and eliminates Blob trigger polling delays
Why it's wrong here
The Premium plan eliminates cold starts and provides VNET integration, but it does not change the fundamental polling mechanism of the Blob Storage trigger. The polling delay on large accounts affects all hosting plans equally.
Quick reference
Cloud Service Model Comparison
| Model | You Manage | Provider Manages | Examples |
|---|---|---|---|
| IaaS | OS, runtime, apps, data | Hardware, hypervisor, networking | EC2, Azure VMs, GCP Compute Engine |
| PaaS | Apps and data | OS, runtime, middleware, hardware | Elastic Beanstalk, Azure App Service |
| SaaS | Data and settings only | Everything else | Microsoft 365, Salesforce, Workday |
| FaaS / Serverless | Function code only | Infra, scaling, runtime | Lambda, Azure Functions, Cloud Run |
| CaaS | Containers and apps | Kubernetes, OS, hardware | EKS, AKS, GKE |
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This AZ-204 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-204 exam.