Accurate time clock12/15/2023 Stratum 2 is a pool of NTP servers synchronizing to Stratum 1 devices.Stratum 1 is Facebook atomic clock synchronizing with a GNSS.Stratum 0 is a layer of satellites with extremely precise atomic clocks from a global navigation satellite system (GNSS), such as GPS, GLONASS, or Galileo.Building an NTP service at scaleįacebook NTP service is designed in four layers, or strata: One of the most popular approaches for addressing that is to “ smear” the leap second, which means to change the time in very small increments across multiple hours. Servers, however, can miss a ton of transactions or events or experience a serious software malfunction when they expect time to go forward continuously. For humans, adding or removing a second creates an almost unnoticeable hiccup when watching a clock. Because of the Earth’s rotation irregularities, we occasionally need to add or remove a second from time, or a leap second. Leap secondīefore we dive into the details of our NTP service, we need to look at a phenomenon called a leap second. 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. Chrony also forms the foundation of our Facebook public NTP service, available from. 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. For that we tested chrony, a modern NTP server implementation with interesting features. We need to sync all the servers across many data centers with sub-millisecond precision. 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. Devices all over the world rely on Network Time Protocol (NTP) to stay synchronized to a more accurate clock over packet-switched, variable-latency data networks.Īs Facebook’s infrastructure has grown, time precision in our systems has become more and more important. Incorrect time can lead to issues, such as missing an important reminder or failing a spacecraft launch. Many clocks contain inaccurate internal oscillators, which can cause seconds of inaccuracy per day and need to be periodically corrected. UPDATE: To continue our support of this public NTP service, we have open-sourced our collection of NTP libraries on GitHub.Īlmost all of the billions of devices connected to the internet have onboard clocks, which need to be accurate to properly perform their functions.
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