FreeBSD Security Officer Emeritus Colin Percival blogs about an issue with running FreeBSD on Amazon’s EC2 “C5” instances. Please see his notice if you are currently running this or plan to do so. See the link below for the full report. 

Last week, Amazon released the “C5” family of EC2 instances, continuing their trend of improving performance by both providing better hardware and reducing the overhead associated with virtualization. Due to the significant changes in this new instance family, Amazon gave me advance notice of their impending arrival several months ago, and starting in August I had access to (early versions of) these instances so that I could test FreeBSD on them. Unfortunately the final launch date took me slightly by surprise — I was expecting it to be later in the month — so there are still a few kinks which need to be worked out for FreeBSD to run smoothly on C5 instances. I strongly recommend that you read the rest of this blog post before you use FreeBSD on EC2 C5 instances. (Or possibly skip to the end if you’re not interested in learning about any of the underlying details.)

Original post: http://www.daemonology.net/blog/2017-11-17-FreeBSD-EC2-C5-instances.html

Hacker News discussion: https://news.ycombinator.com/item?id=15718434