@angrychimp : Thanks. I have got the things I needed. I know Groups can be used by others, but my focus was specifically to locate groups which are open to Internet and then filter how many or which ec2 are directly associated with it. so I had figured it out.
@angrychimp Thanks for the fargate reference and the doc. The doc page for register-container-instance seems to say, as I thought, that container registration normally happens "automatically". That's also what the course implies.