AWS Certified Developer – Associate (DVA-C02) — Question 309

A developer is investigating an issue in part of a company's application. In the application, messages are sent to an Amazon Simple Queue Service (Amazon SQS) queue. The AWS Lambda function polls messages from the SQS queue and sends email messages by using Amazon Simple Email Service (Amazon SES). Users have been receiving duplicate email messages during periods of high traffic.

Which reasons could explain the duplicate email messages? (Choose two.)

Answer options

• A. Standard SQS queues support at-least-once message delivery.
• B. Standard SQS queues support exactly-once processing, so the duplicate email messages are because of user error.
• C. Amazon SES has the DomainKeys Identified Mail (DKIM) authentication incorrectly configured.
• D. The SQS queue's visibility timeout is lower than or the same as the Lambda function's timeout.
• E. The Amazon SES bounce rate metric is too high.

Correct answer: A, D

Explanation

Standard SQS queues guarantee at-least-once delivery, meaning duplicate messages can occasionally be delivered, especially during high-traffic periods. Additionally, if the SQS queue's visibility timeout is shorter than or equal to the Lambda function's timeout, a message might become visible again and be processed by another Lambda instance before the first execution finishes and deletes it. Other options like DKIM configuration, high bounce rates, or claims of exactly-once delivery for Standard SQS are incorrect.