EC2(TM) users are urged to read the Errata Notes for FreeBSD 11.0-RELEASE regarding an issue discovered very late in the release cycle that may cause the system to hang during the boot process when upgrading from previous FreeBSD versions. New EC2(TM) installations are not affected, but existing installations running earlier releases are advised to wait until the issue is resolved in an Errata Notice before upgrading.
This is discussed on BSD Now 162 https://www.youtube.com/watch?v=fJ-mgwxhNvo