Current situation

Flat car Ami released for AWS cloud by default use SNTP as the time server instead of chrony or NTP which resolve upto multiple ms accuracy.

We checked 2 instance & noticed offset of about < 250 ms we did not notice any use SNTP config, atleast based on the OS config. The problem we noticed was with the interface in the path having resolution until Seconds but not in ms with SNTP

Flat car OS uses Systemd-timesyncd & i’m unable find any flag or config which can remove the offset to ms accuracy btw nodes. We could not find any way to set the time Precision with SNTP but in any case, the OS must resolve time to ms accuracy by default

$ timedatectl show-timesync --all
LinkNTPServers=
SystemNTPServers=
RuntimeNTPServers=
FallbackNTPServers=0.flatcar.pool.ntp.org 1.flatcar.pool.ntp.org 2.flatcar.pool.ntp.org 3.flatcar.pool.ntp.org
ServerName=0.flatcar.pool.ntp.org
ServerAddress=167.172.70.21
RootDistanceMaxUSec=5s
PollIntervalMinUSec=32s
PollIntervalMaxUSec=34min 8s
PollIntervalUSec=4min 16s
NTPMessage={ Leap=0, Version=4, Mode=4, Stratum=2, Precision=-23, RootDelay=1.296ms, RootDispersion=47.546ms, Reference=6D31CFAE, OriginateTimestamp=Thu 2024-02-01 11:23:41 UTC, ReceiveTimestamp=Thu 2024-02-01 11:23:41 UTC, TransmitTimestamp=Thu 2024-02-01 11:23:41 UTC, DestinationTimestamp=Thu 2024-02-01 11:23:41 UTC, Ignored=no, PacketCount=3, Jitter=20.034ms }
Frequency=-12022283

Impact

Machine time offset varies btw < 250 ms

Ideal future situation

Support chrony or enable NTPD by default in AWS ami to resolve the accuracy issue

Additional information

Addition github issues reported & references