"Security groups (which define what IPs can access what ports, similar to basic IPTables firewall rules) cannot be shared between EC2-Classic and EC2-VPC,"<p>That is no longer true. In December 2014 Amazon launched ClassicLink, which lets you add EC2-Classic instances to VPC security groups.<p><a href="https://aws.amazon.com/blogs/aws/classiclink-private-communication-between-classic-ec2-instances-vpc-resources/" rel="nofollow">https://aws.amazon.com/blogs/aws/classiclink-private-communi...</a><p><a href="http://www.youtube.com/watch?v=HexrVfuIY1k&t=33m33s" rel="nofollow">http://www.youtube.com/watch?v=HexrVfuIY1k&t=33m33s</a>