AWS SDK for .NET Documentation
GroupId Property
AmazonAmazon.EC2.ModelModifyInstanceAttributeRequestGroupId Did this page help you?   Yes   No    Tell us about it...
New security groups that an instance belongs to.
Declaration Syntax
C#
public List<string> GroupId { get; set; }
Remarks
This is applicable only to instances running in a VPC. Use this parameter when you want to change the security groups an instance is in. The new set of groups you specify replaces the current set. You must specify at least one group, even if it's just the default security group in the VPC.

Assembly: AWSSDK (Module: AWSSDK) Version: 1.5.60.0 (1.5.60.0)