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Comment by deelowe | Hacker News Reader

I was referring to the amazon time sync service which I imagine has pretty tight timing requirements (similar to spanner), not NTP.

Also, how exactly would GPS work at scale for 10,000s of servers within 1000s of racks within a DC?

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"Amazon provides the Amazon Time Sync Service, which is accessible from all EC2 instances, and is also used by other AWS services. This service uses a fleet of satellite-connected and atomic reference clocks in each AWS Region to deliver accurate current time readings of the Coordinated Universal Time (UTC) global standard through Network Time Protocol (NTP). The Amazon Time Sync Service automatically smooths any leap seconds that are added to UTC.

"The Amazon Time Sync Service is available through NTP"

https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/set-time...

As I understand it, “amazon time sync service” is just a bunch of NTP servers run by Amazon. Their ClockBound library calculates error bounds the same way you would if you were using a different NTP server: |Local Offset| + Root Dispersion + (Root Delay / 2)

>how exactly would GPS work at scale for 10,000s of servers

GPS module (+ GPSDO + Rb clock optional) -> SBC running NTP server -> machines running NTP client

I’m not sure what you meant by “clocks on the system board” but if you’re talking about the system clock on the NTP server or the NTP client, it really doesn’t matter. Any old crystal on the NTP server is accurate enough to stay locked to a PPS input. The clients are limited by NTP so their clocks don’t really matter either.

I see. This different than what I thought it was. If it is indeed a simple NTP server, this makes sense.

By using PTP in the data center LAN to distribute the GPS time locally.

https://en.m.wikipedia.org/wiki/Precision_Time_Protocol

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