1. use RDS
2. if you want to run your own you’d better know how HA setups work and you can lose at least a machine at ANY point in time (not just when AWS warns you the hardware is failing)
RDS is a joke unless you use aurora. Necessary downtime for a database upgrade? Try again Amazon.
what engine are you using? is it in an multi-AZ setup?
Live migration can help you in that case.