Question

You want to modify the security group rules while it is being used by multiple EC2 instances. Will you be able to do that? If yes, will the new rules be implemented on all previously running EC2 instances that were using that security group?

Answer 1

Yes, the security group that is being used by multiple EC2 instances can be modified. The changes will be implemented immediately and be applied to all the previously running EC2 instances without restarting the instances