If you have chosen Multi-AZ deployment, in the event of a planned or unplanned outage of your primary DB
Instance, Amazon RDS automatically switches to the standby replica. The automatic failover mechanism simply
changes the ____ record of the main DB Instance to point to the standby DB Instance.

A.
DNAME

B.
CNAME

C.
TXT

D.
MX

Explanation:
“When failing over, Amazon RDS simply flips the canonical name record (CNAME) for your DB Instance to
point at the standby, which is in turn promoted to become the new primary”
https://aws.amazon.com/rds/faqs/