I feel compelled to be "that guy" for a second and just mention that while this is convenient, it makes you blatantly vulnerable to man-in-the-middle attacks. I mean, host keys exist for a reason. Sure, for many people security may not "matter" but I still think it's good to be aware when you're doing something that's way out of bounds.

I don't know how EC2 instances work in detail, but I imagine there must be a way to get a hold of the host key via an API or something when it's deployed (or maybe at any point) so that integrity could be kept without creating annoyance. I'd be much more comfortable with a solution that, for example, queries AWS over HTTPS before every connection and updates the host key (if necessary).