问题
Would communicating with an RDS instance through a public endpoint (RDS in a public subnet) incur more data transfer costs vs one in a private subnet, given that both RDS and the entity accessing it are in the same AZ?
回答1:
The DNS Name of the Amazon RDS db instance should resolve to a private IP address when used within the VPC. Thus, the only potential charge is 2¢/GB between AZs (1¢ in and 1¢ out).
If they are both in the same AZ, there should be no data transfer charge.
Accessing via a public IP address would incur 1¢/GB, but this does not doubly-charge with the "between AZ" charge. So, same potential cost.
If accessing the RDS instance from the Internet, then additional Data Transfer charges would apply for outbound data.
来源：https://stackoverflow.com/questions/59306308/rds-data-transfer-costs-public-vs-private-endpoints