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Event-driven automation: SOA-C03 study notes and practice questions

What to know about Event-driven automation for the SOA-C03 exam, from the Deployment, Provisioning, and Automation domain (22% of the exam guide), then 1 free question to test it. Part of the SOA-C03 study guide.

Last verified against current AWS documentation ·How we write our questions

What to know for the exam

These questions ask how to run work automatically when something happens, without polling or servers.

Event sources

Source Example
S3 event notifications Object created or deleted → Lambda, SQS, SNS, or EventBridge
EventBridge rules EC2 state change, Auto Scaling events, Health events, API calls via CloudTrail, findings
EventBridge Scheduler Every night at 2:00 in a time zone
CloudWatch alarms State change → EventBridge or SNS
DynamoDB Streams / Kinesis Item changes → Lambda
SQS Messages → Lambda event source mapping

Lambda for operations

  • Good for short tasks (up to 15 minutes): tag resources, clean up snapshots, notify teams, call APIs.
  • Needs an execution role with only the permissions it uses.
  • Asynchronous invocations retry twice by default; configure a dead-letter queue or on-failure destination to keep failed events.
  • Reserved concurrency can cap a function, or set to zero to stop it in an emergency.
  • Logs go to CloudWatch Logs; watch Errors, Throttles and Duration.

Avoiding loops

A function that writes to the same bucket or prefix that triggers it can call itself forever. Use separate buckets or prefixes for input and output, and filter events by prefix or suffix. Lambda’s recursive loop detection stops some loops automatically, but don’t rely on it.

Step Functions

For multi-step automation with waits, retries, branches and human approval, use AWS Step Functions instead of chaining Lambda functions.

Common traps

  • Polling with a cron job when an event source exists.
  • No DLQ or destination for important asynchronous events.
  • Overly broad execution roles.

Try the 1 practice question

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Question 1

Medium ·Link to this question (question 1)

A ski resort's guests upload photos to an S3 bucket.

An S3 Event Notification for all object-created events invokes a Lambda function that writes a resized copy of each photo back into the same bucket.

After the function was deployed, Lambda invocations and S3 request costs rose sharply, and resized copies of resized copies started to appear.

What should a CloudOps engineer do to fix this?

Choose one answer.

  1. A. Set the function's reserved concurrency to 10 so that the number of copies the function can create at once is limited.
  2. B. Turn on S3 Versioning so that each resized copy is stored as a new version of the original rather than as a new object.
  3. C. Replace the S3 Event Notification with an EventBridge rule that matches Object Created events from the bucket.
  4. D. Upload to an uploads/ prefix, filter the notification on it, and write resized copies to resized/.
Show the answer and explanation

Answer: D

Explanation

A function that writes back to the same location that triggers it creates a recursive loop. Separate input and output with key name prefix filters or a second bucket so that the function's writes do not match the trigger. Lambda can detect and stop some recursive loops, but the design should not rely on that.

Study

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