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Thank you for posting your question.
The scenario is actually based on the event where an Amazon Aurora failover occurs. You have to check if your client application is caching the DNS data of your DB instances, and set the appropriate TTL. Keep in mind that in the actual AWS exam, there would be scenarios where it won’t explicitly mention certain details, such as the client application that caches the DNS data.
This is supported in the official AWS documentation:
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If your client application is caching the Domain Name Service (DNS) data of your DB instances, set a time-to-live (TTL) value of less than 30 seconds. The underlying IP address of a DB instance can change after a failover. Thus, caching the DNS data for an extended time can lead to connection failures if your application tries to connect to an IP address that no longer is in service. Aurora DB clusters with multiple read replicas can experience connection failures also when connections use the reader endpoint and one of the read replica instances is in maintenance or is deleted.
Reference:
https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/Aurora.BestPractices.html
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