Documentation changes are given below for knife-ec2 version 0.14.0.
The --security-group-id option allows the user to specify the security group id for server and is required when using VPC. Multiple security groups may be specified by using this option multiple times, e.g. -g sg-e985168d -g sg-e7f06383 -g sg-ec1b7e88.
The previous option for specifying security groups, --security-group-ids (plural), is deprecated in favor of the --security-group-id option which mimics the more standard behavior for supplying multiple arguments across the ecosystem. This option will be removed in future release.