Building a more accurate time service at Facebook scale
> As Facebook’s infrastructure has grown, time precision in our systems has become more and more important. We need to know the accurate time difference between two random servers in a data center so that datastore writes don’t mix up the order of transactions. We need to sync all the servers across many data centers with sub-millisecond precision. For that we tested chrony, a modern NTP server implementation with interesting features. During testing, we found that chrony is significantly more accurate and scalable than the previously used service, ntpd, which made it an easy decision for us to replace ntpd in our infrastructure. Chrony also forms the foundation of our Facebook public NTP service, available from time.facebook.com. In this post, we will share our work to improve accuracy from 10 milliseconds to 100 microseconds and how we verified these results in our timing laboratory.