If you ever need to take over management of an AWS farm, it’s very likely you will need to attach SG to all instances. Be that for monitoring or access. Here is a bash script to add 1 SG to all instances.

You will need to first setup a profile on awscli. Then run the script with the profile name as first argument, and the SG id as the second.

Note: The script will not work on instances with multiple NICs