DEA-C01 practice question: Event triggers and schedules (1 of 2)
Data Ingestion and Transformation A free question from our original DEA-C01 practice exam. Try it, then open the answer to see why each option is right or wrong.
A solar installer's field engineers upload inspection CSV files to an Amazon S3 bucket under a uploads/ prefix. Each new file must start a Step Functions workflow that validates and loads it within a minute of arrival. Files outside uploads/ must not start the workflow.
The team does not want a Lambda function that lists the bucket on a timer, because most minutes have no uploads and the list calls add cost.
Which approach meets these requirements?
Choose one answer.
AA. Turn on S3 Event Notifications to EventBridge, and add a rule matching the uploads/ prefix and .csv suffix that starts the workflow.
BB. Create an hourly AWS Glue crawler on the bucket, and start the workflow from the crawler's completion event.
CC. Run a Lambda function every minute that lists the uploads/ prefix and starts the workflow for any object it has not seen before.
DD. Enable S3 Event Notifications to publish to an Amazon SNS topic, and subscribe the Step Functions workflow to the topic.
Show the answer and explanation
Answer: A
A. Right: Correct. S3 sends object events to EventBridge once it is enabled on the bucket, and an event pattern can match the object key prefix and suffix. The rule starts the workflow directly, with no polling and no cost while no files arrive. Learn more: Using EventBridge with Amazon S3 (opens in a new tab)
B. Wrong: A crawler runs on its own schedule, so files would wait up to an hour before the workflow starts. It also scans the bucket on every run, which is the cost the team wants to avoid.
C. Wrong: This meets the prefix rule, but it runs on a timer and makes list calls every minute, even when nothing is uploaded. It also needs state tracking for objects it has already seen.
D. Wrong: Amazon SNS cannot start a Step Functions execution as a subscriber, so this design would need another service in between. The team asked for a direct trigger on the uploads prefix, and this adds a moving part.
Explanation
Event-driven triggers start work when a file arrives, with no polling. When S3 Event Notifications go to EventBridge, a rule can match the key prefix and suffix and start the target directly. Timers, crawlers and topics that cannot start the workflow all miss one of the requirements.
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