Event triggers and schedules: DEA-C01 study notes and practice questions
What to know about Event triggers and schedules for the DEA-C01 exam, from the Data Ingestion and Transformation domain (34% of the exam guide), then 2 free questions to test it. Part of the DEA-C01 study guide.
These questions ask how to start a job automatically, as soon as data arrives or at the right time.
Event-driven triggers
Trigger
Notes
S3 Event Notifications to Lambda, SQS or SNS
Simple, per-bucket; filter by prefix and suffix
S3 events to Amazon EventBridge
Turn on EventBridge delivery for the bucket; rules can filter on many fields and send to many targets, including Step Functions and Glue workflows
Lambda event source mappings
Poll Kinesis, DynamoDB Streams, SQS, MSK and others, and invoke a function with batches
Glue triggers
Start jobs and crawlers on a schedule, on demand, on job events (conditional), or from EventBridge events
MWAA sensors
Airflow tasks that wait for a file or condition
Schedules
EventBridge Scheduler runs one-time or recurring schedules (cron or rate) with time zones, so a “2:00 a.m. local time” job follows daylight saving changes. It has retries and dead-letter queues, and calls thousands of APIs directly.
EventBridge rules with cron expressions run in UTC only.
Glue scheduled triggers, Step Functions started by a schedule, and Airflow DAG schedules.
Choosing
“Start processing as soon as each file arrives, no polling”: an S3 event (notification or EventBridge).
“Several workflows react to the same upload”: S3 → EventBridge with several rules.
“Run daily at 6:00 in New York time”: EventBridge Scheduler with the America/New_York time zone.
Common traps
Cron jobs on an EC2 instance. Use EventBridge Scheduler.
UTC schedules drifting an hour after daylight saving changes: use Scheduler with a time zone.
S3 notifications for a target they don’t support (such as Step Functions directly): route through EventBridge.
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.
A dental chain has clinics in New York, Chicago and Denver, and it runs a nightly load of appointment data. Each regional load must start at 2:00 AM local time, and it must keep that local time through daylight saving changes. Once started, the load runs its Glue jobs in order and stops if one of them fails.
The team wants the schedules managed in AWS, with no cron jobs on servers.
Which TWO options meet these requirements? (Choose two.)
Choose two answers.
AA. Create a Glue scheduled trigger with a cron expression of 2:00 AM UTC, and edit the expression by hand each time daylight saving time starts or ends.
BB. Create an EventBridge Scheduler schedule per region with its IANA time zone, targeting a Step Functions state machine for the Glue jobs.
CC. Create an EventBridge rule with the cron expression 0 2 * * ? * for each region, and let the rule's target start the Glue jobs.
DD. Create an MWAA DAG with a timezone-aware schedule for each region, and let it run the Glue jobs in sequence with failure handling.
EE. Run a Lambda function that sleeps until 2:00 AM local time and then starts the jobs, using a long-running loop for each region.
B. Right: Correct. EventBridge Scheduler accepts an IANA time zone for each cron schedule and adjusts automatically for daylight saving time. A Step Functions state machine can run the Glue jobs in sequence and stop the run when one job fails. Learn more: Schedule types in EventBridge Scheduler (opens in a new tab)
A schedule written in UTC cannot follow local clocks through daylight saving changes, so the two correct options use time zones. EventBridge Scheduler and an Airflow DAG can both hold a local start time, and each can run the Glue jobs in order and stop when one fails. The UTC cron options and the sleeping function miss those requirements.
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