Using IPs for communication to Amazon RDS instances is inadvisable. You'd have to use WAN addresses outside of EC2, and LAN addresses inside of EC2. Addressing

Using IPs for communication to Amazon RDS instances is inadvisable. You'd have to use WAN addresses outside of EC2, and LAN addresses inside of EC2. Addressing them by domain resolves this. Additionally I don't think Amazon guarantees your box will be accessible on the same IP addresses after Multi-AZ failovers.