AZ-204 Develop Azure compute solutions Practice Question
Which TWO Azure services can be used to trigger an Azure Function when a new blob is added to an Azure Storage container? (Choose two.)
⚠ Common exam trap
Many exam-takers assume only the Blob Storage trigger can react to blob creation, overlooking Event Grid as a valid alternative, or they mistakenly think Queue Storage or Cosmos DB triggers can be repurposed for blob events.
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 Event Grid trigger
Option A (Azure Event Grid trigger) is correct because Azure Storage integrates with Event Grid to publish a BlobCreated event when a new blob is uploaded, and an Azure Function with an Event Grid trigger subscribes to that event to fire in near real time. Option C (Azure Blob Storage trigger) is correct because it is the native Azure Functions binding that monitors a specified storage container and invokes the function whenever a new or updated blob is detected. Option B (Azure Queue Storage trigger) is not correct because it fires on messages placed in a queue, not on blob creation, unless additional code writes such messages. Option D (Azure Cosmos DB trigger) is not correct because it reacts to changes in a Cosmos DB container's change feed, not to Azure Storage blobs. Option E (HTTP trigger) is not correct because it requires an inbound HTTP request and does not natively detect new blobs.
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 Event Grid trigger
Why this is correct
An Azure Event Grid trigger enables an Azure Function to react to events published by various Azure services, including Azure Blob Storage. When configured, Event Grid subscribes to specific events, such as a "Blob Created" event from a storage account, and then pushes that event to the function endpoint. This provides a highly scalable, low-latency, and reliable event-driven architecture, allowing the function to process the new blob almost instantaneously.
- ✗
Azure Queue Storage trigger
Why it's wrong here
An Azure Queue Storage trigger is designed to activate an Azure Function when a new message is added to a specified Azure Storage Queue. This trigger is specifically for processing discrete messages placed into a queue for asynchronous processing, not for monitoring or reacting to events occurring within Azure Blob Storage containers. It operates on the principle of message consumption, not external resource change detection.
- ✓
Azure Blob Storage trigger
Why this is correct
The Azure Blob Storage trigger directly integrates with Azure Storage accounts, automatically invoking an Azure Function when a new or updated blob is detected in a specified container. This trigger monitors the designated blob container for changes, typically through a polling mechanism or internal notifications, and passes the blob's metadata and content to the function for processing. It's a straightforward way to react to blob lifecycle events.
- ✗
Azure Cosmos DB trigger
Why it's wrong here
An Azure Cosmos DB trigger specifically responds to changes occurring within an Azure Cosmos DB container, leveraging the service's change feed functionality. This trigger is designed for scenarios where a function needs to process new inserts, updates, or deletes of documents in a NoSQL database. It has no direct mechanism to monitor or react to events originating from Azure Blob Storage.
- ✗
HTTP trigger
Why it's wrong here
An HTTP trigger provides a function with a callable HTTP endpoint, allowing it to be invoked by an explicit HTTP request from any client or service. This trigger operates on a request-response model, requiring an external entity to actively send a web request to the function's URL. It does not automatically react to passive events like a blob being created in storage; it waits for an inbound network call.
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
Cosmos DB Partition Key Selection
Key term
Azure Event Grid
Azure Event Grid is a fully managed event routing service that allows applications and services to react to events in real time using a publish-subscribe model.
Key term
Durable Functions
Durable Functions is an extension of Azure Functions that lets you write stateful workflows in code, managing complex sequences of tasks, retries, and delays automatically.
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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.