The one thing you can’t do with Let’s Encrypt is generate a certificate with a CN of localhost which, since browsers are getting really picky about mixed HTTP/HTTPS content, is a real issue with local development using certain web features.
I’ve also struggled with this. Is there an elegant solution that you’re aware of? Everything I’ve tried feels really rickety.
I've been using cfssl[1] to generate a root certificate + a localhost certificate and then trusting the root.