We have an existing EC2 Server 2008 instance in a VPC with an elastic IP associated to the eth0 network interface. We added an additional network interface, eth1, to the instance and this interface also has an elastic IP address that we are binding to a different website.
Before making this change, the instance was recognized from outside the Amazon network by the elastic IP address attached to the eth0 network interface. After rebooting the server, the server is now recognized outside of the network as the elastic IP address attached to network interface eth1.
When I say recognized, I mean that outside resources are now seeing the instance as the elastic ip address attached to the secondary network interface. Using http://whatismyipaddress.com/ from the server is show the elastic ip address attached to the eth1 network interface instead of the eth0 network interface. As this server connects to other outside services that have restrictions on what ip addresses are able to make connections, it is now being blocked. It is also a mail server, and I prefer to stay on the ip address that has a reputation built.
How can I make the server appear to the outside as the elastic ip address that I have associated to the eth0 network interface instead of the elastic ip address associated to eth1?