3.5 KiB
Monitoring time sync with node_exporter
ntp collector
This collector is intended for usage with local NTP daemons including ntp.org, chrony, and OpenNTPD.
Note, some chrony packages have local stratum 10 configuration value making chrony a valid server when it is unsynchronised. This configuration makes one of the heuristics that derive node_ntp_sanity unreliable.
Note, OpenNTPD does not listen for SNTP queries by default. Add listen on 127.0.0.1 to the OpenNTPD configuration when using this collector with that package.
node_ntp_stratum
This metric shows the stratum of the local NTP daemon.
Stratum 16 means that clock are unsynchronised. See also aforementioned note about default local stratum in chrony.
node_ntp_leap
Raw leap flag value. 0 – OK, 1 – add leap second at UTC midnight, 2 – delete leap second at UTC midnight, 3 – unsynchronised.
OpenNTPD ignores leap seconds and never sets leap flag to 1 or 2.
node_ntp_rtt
RTT (round-trip time) from node_exporter collector to local NTPD. This value is used in sanity check as part of causality violation estimate.
node_ntp_offset
Clock offset between local time and NTPD time.
ntp.org always sets NTPD time to local clock instead of relaying remote NTP time, so this offset is irrelevant for this NTPD.
This value is used in sanity check as part of causality violation estimate.
node_ntp_reference_timestamp_seconds
Reference Time. This field show time when the last adjustment was made, but implementation details vary from "local wall-clock time" to "Reference Time field in incoming SNTP packet".
time() - node_ntp_reference_timestamp_seconds and
node_time_seconds - node_ntp_reference_timestamp_seconds represent some estimate of
"freshness" of synchronization.
node_ntp_root_delay and node_ntp_root_dispersion
These values are used to calculate synchronization distance that is limited by
collector.ntp.max-distance.
ntp.org adds known local offset to announced root dispersion and linearly
increases dispersion in case of NTP connectivity problems, OpenNTPD does not
account dispersion at all and always reports 0.
node_ntp_sanity
Aggregate NTPD health including stratum, leap flag, sane freshness, root
distance being less than collector.ntp.max-distance and causality violation
being less than collector.ntp.local-offset-tolerance.
Causality violation is lower bound estimate of clock error done using SNTP,
it's calculated as positive portion of abs(node_ntp_offset) - node_ntp_rtt / 2.
timex collector
This collector exports state of kernel time synchronization flag that should be maintained by time-keeping daemon and is eventually raised by Linux kernel if time-keeping daemon does not update it regularly.
Unfortunately some daemons do not handle this flag properly, e.g. chrony-1.30
from Debian/jessie clears STA_UNSYNC flag during daemon initialisation and
does not indicate clock synchronization status using this flag. Modern chrony
versions should work better. All chrony versions require rtcsync option to
maintain this flag. OpenNTPD does not touch this flag at all till
OpenNTPD-5.9p1.
On the other hand combination of sync_status and offset exported by timex
module is the way to monitor if systemd-timesyncd does its job.