It is a common practice to enable mutli-AZ when deploy RDS in AWS to provide high availability. That’s not all. There is one more thing you need to check – DNS cache setting of your applications/codes. If you overlook it, the hight availability design may not work as you expect.
Imagine that when RDS detects the failure of the primary DB, it automatically promotes the standby DB to primary and update the DNS to point the new primary DB. If the application cache the DNS longer than the time that RDS takes to failover, then your application will run into an issue.
Here is a example of the DNS cache settings in JVM.