Change the security group associated with an ECS NIC.
in the upper left corner and select your region and project.
and choose Computing > Elastic Cloud Server.The Change Security Group dialog box is displayed.

You can select multiple security groups. In such a case, the access rules of all the selected security groups apply to the ECS.
To create a security group, click Create Security Group.
Using multiple security groups may deteriorate ECS network performance. We recommend that you associate no more than five security groups with each ECS.