Each container on an instance can now have its own security group, and does not need to share security rules with other containers. You can attach security groups to an ENI, and each ENI on an instance can have a different security group. You can map a container to the IP address of a particular ENI to associate security group(s) per container. Load balancing using IP addresses also allows multiple containers running on an instance use the same port (say port 80). The ability to use the same port across containers allows containers on an instance to communicate with each other through well-known ports instead of random ports.