Defined in github.com/aws/aws-sdk-go/service/ec2/api.go
The number of secondary private IP addresses to assign to a network interface. When you specify a number of secondary IP addresses, Amazon EC2 selects these IP addresses within the subnet range. You can't specify this option and specify more than one private IP address using privateIpAddresses.
The number of IP addresses you can assign to a network interface varies by instance type. For more information, see Private IP Addresses Per ENI Per Instance Type (http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-eni.html#AvailableIpPerENI) in the Amazon Elastic Compute Cloud User Guide.