A company has built an application that uses an Amazon Simple Queue Service (Amazon SQS)...

SQS Standard queues provide at-least-once delivery; they can, by design, deliver duplicate messages, and you cannot turn that off.

To guarantee no duplicates to consumers, AWS provides SQS FIFO queues with exactly-once processing semantics in conjunction with deduplication.

The minimal change to achieve this behavior is to:

Recreate the queue as a FIFO queue and

Enable content-based deduplication, so SQS automatically deduplicates messages with identical bodies within the deduplication window.

Why others are not correct:

A: Long polling reduces empty responses and costs but does not eliminate duplicates.

C: Content-based deduplication is available only for FIFO queues, not for standard queues—so you cannot “modify” a standard queue this way.

D: Moving to Amazon MQ is a much bigger architectural change and adds more operational overhead; it’s not the “fewest changes” approach.