You can specify multiple private IPv4 and IPv6 addresses for your instances. The number of network interfaces and private IPv4 and IPv6 addresses that you can specify for an instance depends on the instance type.
Things to note before creating a assigning Multiple EIP to Instances.
- Classic EC2 instances can only have a single Elastic IP address associated (attached) to them.
- To have multiple IP addresses associated with your instance. You must use VPC and setup multiple network interfaces on your instance.
INFO: AWS announced sometime between 2012 and 2014 that a single ENI can have multiple EIPs assigned to it. This answer, and the question, are no longer relevant as a result.