CV0-004 Deployment Practice Question
A developer is deploying a serverless function that processes images uploaded to an S3 bucket. The function should be triggered automatically whenever a new object is created in the bucket. Which event source should be configured to invoke the Lambda function?
⚠ Common exam trap
CV0-004 often tests the misconception that any AWS service that can invoke Lambda is a valid event source for S3 events, but the key is that S3 itself must be configured as the event source for direct, automatic triggering.
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
✓
Amazon S3
Amazon S3 is the correct event source because it natively supports event notifications that can directly invoke AWS Lambda functions when objects are created, deleted, or modified in a bucket. This integration is built into the S3 service and requires no additional services or polling. The developer simply configures an S3 bucket notification to trigger the Lambda function on 's3:ObjectCreated:*' events, which is the standard serverless pattern for processing uploaded files.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Amazon SQS
Why it's wrong here
SQS is a message queue; Lambda can poll it, but it is not a direct S3 event trigger.
- ✗
Amazon EventBridge
Why it's wrong here
EventBridge can route S3 events, but configuring it adds an intermediary rule layer where S3 can invoke Lambda directly. EventBridge is the right choice when fanning events to multiple targets, filtering by detail, or integrating SaaS and custom applications.
- ✓
Amazon S3
Why this is correct
Amazon S3 event notifications invoke Lambda directly when objects are created, satisfying the automatic trigger requirement. Configuring the bucket's `s3:ObjectCreated:*` event type with the function as destination removes polling entirely. This is the native push integration for object-creation events, unlike pull-based sources such as Kinesis or DynamoDB Streams.
- ✗
API Gateway
Why it's wrong here
API Gateway invokes Lambda only in response to inbound HTTP requests, not to object creation in a bucket. It is tempting because it is the standard front door for serverless APIs, and it is correct when clients must call the function over HTTPS.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
Go deeper
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official CompTIA exam blueprint
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