Cannot connect Q app to RDS

This issue could arise if the host address is a multicast or loopback address, which are typically used for internal network communication.

Another potential factor is the difference in regions between your RDS instance and your application. AWS resources in different regions are isolated from each other, so you might need to set up VPC peering or use a VPN to establish a connection between the two regions.

Additionally, an SSL/TLS certificate attached to the RDS instance could impact the connection. This certificate encrypts the connection between your application and the RDS instance. If the certificate is not properly configured or if your application does not accept certificate chains, the connection may fail. You may need to use an intermediate certificate specific to your AWS Region.