I am planning to have a multi server architecture in amazon EC2 where the servers need to talk to each other. These servers need to be located in different amazon regions (different datacenters). Can I just use the internal network of the amazon ec2? What are the security issues? Should I mandatorily use Amazon VPC in this setup.
Jam ,
If you are planning to create instances on different regions then go for VPC ,because VPC gives you more security .You can restrict these machines for limited external access also . As security part , VPC is better than classic EC2 instances ,as you can even only allow VPC to VPC connections also .