I've got many ec2 instances and recently added a Virtual Private Cloud at amazon too. On the VPC subnet 10.0.0.0/8 the host 10.0.0.88 can reach the internet at large through an Internet Gateway Device igw-xxxxxx, but I don't know how to authorize that host to access my non-VPC ec2 instances in the outside-the-VPC security group rules.
I'm used to authorizing specific source IPs or the names of other ec2 security groups to connect to the non-VPC hosts, but I can't figure out how to whitelist the VPC host. Whitelisting 10.0.0.88 doesn't make sense as that IP isn't valid outside the VPC, whitelisting igw-xxxxxx gets me "no such security group". I can whitelist the host if I assign it an Elastic IP, but then the traffic isn't going directly internal to the aws structure.
The FAQ makes this sound possible:
Q. Can Amazon EC2 instances within a VPC communicate with Amazon EC2 instances not within a VPC?
A. Yes. If an Internet Gateway has been configured, Amazon VPC traffic bound for Amazon EC2 instances not within a VPC traverses the Internet Gateway and then enters the public AWS network to reach the EC2 instance.