AWS DVA-C02 Drill: Lambda Event Invocation - EventBridge vs S3 Triggers

Jeff’s Note

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Unlike generic exam dumps, ADH analyzes this scenario through the lens of a Real-World Lead Developer.

For DVA-C02 candidates, the confusion often lies in understanding the difference between S3 native event triggers and EventBridge rules for invoking Lambda functions. In production, this is about knowing exactly how to wire up event sources so your Lambda responds instantly to key S3 events without unnecessary polling or scheduling. Let’s drill down.

The Certification Drill (Simulated Question)

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Scenario

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Nova Analytics, a fast-growing startup, is developing a serverless app to process uploaded CSV data files automatically to generate reports. The team has provisioned a dedicated S3 bucket to receive CSV uploads and created a Lambda function to parse and process these CSV files.

The Requirement:

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Configure Lambda so it is invoked immediately whenever a new CSV file is uploaded to their S3 bucket.

The Options

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  - A) Create an Amazon EventBridge rule. Configure the rule with a pattern to match the S3 object created event.  
  - B) Schedule an Amazon EventBridge rule to run a new Lambda function to scan the S3 bucket periodically.  
  - C) Add a trigger to the existing Lambda function. Set the trigger type to EventBridge. Select the Amazon EventBridge rule.  
  - D) Create a new Lambda function to scan the S3 bucket for recently added S3 objects.  
  - E) Add S3 Lifecycle rules to invoke the existing Lambda function.

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leave a comment:

Correct Answer

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A and C.

Quick Insight: The DVA-C02 Imperative

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• Lambda can be triggered directly by S3 events OR indirectly through EventBridge.
• Options A and C together form the correct mechanism: an EventBridge rule captures S3 object-created events, and the Lambda function subscribes to that rule as an EventBridge trigger.
• This approach enables decoupled, event-driven invocation without polling or scheduled scans.

Content Locked: The Expert Analysis

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You’ve identified the answer. But do you know the implementation details that separate a Junior from a Senior?

The Expert’s Analysis

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Correct Answer

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Options A and C

The Winning Logic

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• Option A sets up an EventBridge rule that matches S3 “Object Created” events, including the upload of CSV files.
• Option C attaches that EventBridge rule as a trigger to the existing Lambda function so the Lambda is invoked automatically when matching events occur.
• This pattern leverages EventBridge as the event router and Lambda as the processor, achieving a low-latency event-driven architecture.

The Trap (Distractor Analysis):

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• Why not B? Scheduling a Lambda scan via EventBridge polling the S3 bucket is inefficient, slower, and increases complexity. This introduces delay and unnecessary cost.
• Why not D? Creating another Lambda to scan the bucket is redundant and less scalable compared to event-based invocation.
• Why not E? S3 Lifecycle rules manage object transitions and expiration, not Lambda invocation—they cannot trigger Lambda functions.

The Technical Blueprint

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For Developer / SysOps (Code/CLI Snippet):

# Create EventBridge rule for S3 ObjectCreated events (filter on CSV files)
aws events put-rule --name CsvUploadRule --event-pattern '{
  "source": ["aws.s3"],
  "detail-type": ["Object Created"],
  "detail": {
    "bucket": {
      "name": ["your-bucket-name"]
    },
    "object": {
      "key": [{"prefix": "", "suffix": ".csv"}]
    }
  }
}'

# Add Lambda function as target of the EventBridge rule
aws events put-targets --rule CsvUploadRule --targets "Id"="1","Arn"="arn:aws:lambda:region:account-id:function:YourLambdaFunctionName"

# Add Lambda permission for EventBridge to invoke it
aws lambda add-permission --function-name YourLambdaFunctionName --statement-id EventBridgeInvoke --action 'lambda:InvokeFunction' --principal events.amazonaws.com --source-arn arn:aws:events:region:account-id:rule/CsvUploadRule

The Comparative Analysis

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Real-World Application (Practitioner Insight)

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Exam Rule

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“For the exam, always pick EventBridge when you see complex event routing or multi-service integration but consider native triggers for simple one-to-one events.”

Real World

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“In reality, for simple S3 Upload > Lambda patterns, configuring the S3 bucket notification directly on Lambda is simpler and preferred. However, since this question emphasizes EventBridge, it’s important to know that EventBridge rules can also handle S3 events for more flexible event-driven architectures.”

(CTA) Stop Guessing, Start Mastering

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Disclaimer

This is a study note based on simulated scenarios for the AWS DVA-C02 exam.