Amazon AWS's EC2 started supporting IPv6 earlier this year. When I spun up my new Debian 9 Stretch instance a few months ago it came with IPv6 support. It started out working just fine. However, after one week, consistently, my instance would always lose its IPv6 route. The host would keep its IP address but any attempt to use ping6 or a traceroute6 would return "network unreachable" and ip -6 route would show no gateway. (I even set accept_ra 1 in the network interfaces configuration, among other things that I tried.) Lots of changes to my configuration yielded no results. Since I can't get a console using EC2 the only way to test would be to make a configuration change, reboot, and then wait a week to see if IPv6 still works. So today I finally just removed my AAAA records.