AWS Certified Solutions Architect Professional SAP-C02 Practice Question

An Amazon SQS FIFO queue subscribed to the SNS topic provides each microservice with a durable buffer. With a message retention period of up to 14 days, it easily covers the 12-hour outage window. To meet the 'exactly-once' delivery requirement when subscribing a FIFO queue to a standard SNS topic, content-based deduplication must be enabled on the queue; this prevents duplicate messages published by SNS (which has at-least-once delivery) from being added to the queue. A redrive policy configured with a maxReceiveCount of five sends poison-pill messages to a dead-letter queue (DLQ), preventing them from blocking other messages. This design meets all requirements using managed services and minimal custom code.

• Direct HTTP(S) subscriptions are unsuitable. This pattern lacks a durable, persistent queue to hold messages during the 12-hour outage. While SNS has a configurable retry policy, it relies on the consumer endpoint being available. Furthermore, it provides at-least-once delivery, requiring each microservice to implement custom deduplication logic to meet the 'exactly-once' requirement.
• Amazon Kinesis Data Streams provide at-least-once delivery and would require significant custom code for checkpointing and idempotent processing to prevent duplicates, violating the requirement to minimize custom solutions.
• AWS Step Functions workflows triggered by SNS do not provide a durable buffer for events if the target service is offline for an extended period. The workflow execution would eventually fail after exhausting its retries, and the event would be lost.