Q23 — AWS DVA-C02 Ch.3

Question 23 of 100 | ← Chapter 3

A company uses an AWS Lambda function behind Amazon API Gateway as its application layer. To handle orders under high traffic, the application invokes a POST API from the frontend. The POST API invokes the Lambda function asynchronously. In many cases, orders fail to process. No errors or failures appear in the Lambda application logs.

• A. Check frontend logs for API failures. Manually invoke the POST API using request details from the logs.
• B. Create and inspect the Lambda dead-letter queue (DLQ). Investigate failed invocations and reprocess events. ✓
• C. Check Lambda logs in Amazon CloudWatch for possible errors. Fix the errors.
• D. Ensure caching is disabled for the POST API in API Gateway.

Correct Answer: B. Create and inspect the Lambda dead-letter queue (DLQ). Investigate failed invocations and reprocess events.

Explanation

In asynchronous Lambda invocations, failed invocations (e.g., due to timeouts, exceptions, or permission issues) are automatically sent to a configured dead-letter queue (DLQ) if enabled. Since no errors appear in application logs, the root cause likely resides in invocation-level failures captured only in the DLQ. Option B is correct: creating and inspecting the DLQ reveals failed events, enabling diagnosis and reprocessing. Option A assumes frontend visibility of backend failures, which is unreliable. Option C is ineffective because asynchronous failures do not surface in application logs unless explicitly logged. Option D is irrelevant — caching does not affect asynchronous invocation success or failure. Thus, option B is the appropriate action.