Are you sure your ISV has kept these simple pointers in mind when deploying your multi-module app on AWS??
All Amazon EC2 instances are assigned two IP addresses at launch: a private address (RFC 1918) and a public address that are directly mapped to each other through Network Address Translation (NAT). Private addresses are only reachable from within the Amazon EC2 network. Public addresses are reachable from the Internet.
Amazon EC2 also provides an internal DNS name and a public DNS name which map to the private and public IP addresses respectively. The internal DNS name can only be resolved within Amazon EC2. The public DNS name resolves to the public IP address outside the Amazon EC2 network and the private IP address within the Amazon EC2 network
This private address is associated exclusively with the instance for its lifetime and is only returned to Amazon EC2 when the instance terminates.
Always use the internal address when you are communicating between Amazon EC2 instances. This ensures that your network traffic follows the highest bandwidth, lowest cost, and lowest latency path through our network.
Amazon EC2 instances that access other instances through their public NAT IP address are charged for Regional or Internet data transfer, depending on whether the instances are in the same Region.
To ensure customers are efficiently using elastic IP addresses, Amazon imposes a small hourly charge when these IP addresses are not mapped to an instance. When these IP addresses are mapped to an instance, they are free of charge.
Watch this space for more pointers!!!
Until Next time!!