What happens with Fargate if you need to SSH into the underlying instance? I haven't used it myself, and I'm not sure that it truly abstracts away the EC2 instance, but the description of Fargate always made me assume that to be the case.
I assume eatonphil is correct, but to be honest I’ve never even tried, and in my view that’s actually part of the point: full commitment to immutable infrastructure, made really easy. If something needs to change, I tweak the Dockerfile or the task definition or a config file and redeploy. No more SSH.
There is no underlying instance, it's a fully managed service.