Configure an external NTP relay

This page describes how to configure an external NTP replay for Google Distributed Cloud (GDC) air-gapped appliance.

These steps are only required if you want to synchronize the appliance with external time after being disconnected.

Before you begin

To sync the appliance with external NTP, complete the following steps:

  1. Configure the device and install software

  2. Before you begin, make sure that there is only one NTP relay. To verify, run the following command on the bootstrapper machine:

    kubectl get ntprelay -A

    The output looks like the following example:

    NAMESPACE    NAME           AGE
gpc-system   bi-ntp-relay   4d21h

Configure the NTP relay

  1. Connect the bootstrapper to the appliance device and determine the IP address of the connected interface:

    ifconfig
mgmt: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
    inet 198.18.0.30   netmask 255.255.255.224  broadcast 198.18.0.31
    inet6 fe80::20c:29ff:fea8:fc35  prefixlen 64  scopeid 0x20&lt;link&gt;
...

  2. Edit the ntprelay CR by including the bootstrapper mgmt IP as the upstream IP.

    kubectl edit ntprelay bi-ntp-relay -n gpc-system
ntprelay.system.private.gdc.goog/bi-ntp-relay edited
kubectl get ntprelay bi-ntp-relay -n gpc-system -oyaml

    The output looks like the following example. In this example the IP address for upstreamServers is changed:

    apiVersion: system.private.gdc.goog/v1alpha1
kind: NTPRelay
metadata:
  creationTimestamp: "2025-05-16T08:44:21Z"
  generation: 2
  name: bi-ntp-relay
  namespace: gpc-system
  resourceVersion: "10871409"
  uid: 6cde8e65-791c-4bc6-9a8b-d5c9bf103f8b
spec:
  upstreamServers:
  - 192.0.2.030

  3. Verify the NTP synchronization:

    kubectl get pods -l app.kubernetes.io/name=ntp -n ntp-system -o name | xargs -I {} kubectl exec {} -n ntp-system -- chronyc sources -v; echo

    The output looks like the following:

      .-- Source mode  '^' = server, '=' = peer, '#' = local clock.
/ .- Source state '*' = current best, '+' = combined, '-' = not combined,
| /             'x' = may be in error, '~' = too variable, '?' = unusable.
||                                                 .- xxxx [ yyyy ] +/- zzzz
||      Reachability register (octal) -.           |  xxxx = adjusted offset,
||      Log2(Polling interval) --.      |          |  yyyy = measured offset,
||                                \     |          |  zzzz = estimated error.
||                                 |    |           \
MS Name/IP address         Stratum Poll Reach LastRx Last sample
===============================================================================
^* 192.0.2.026                   1   6    17    43   +286ns[  +36us] +/- 1160us
=? 192.0.2.029                 0   6     0     -     +0ns[   +0ns] +/-    0ns
=? 192.0.2.051                 0   6     0     -     +0ns[   +0ns] +/-    0ns
=? 192.0.2.059            0   6     0     -     +0ns[   +0ns] +/-    0ns

  .-- Source mode  '^' = server, '=' = peer, '#' = local clock.
/ .- Source state '*' = current best, '+' = combined, '-' = not combined,
| /             'x' = may be in error, '~' = too variable, '?' = unusable.
||                                                 .- xxxx [ yyyy ] +/- zzzz
||      Reachability register (octal) -.           |  xxxx = adjusted offset,
||      Log2(Polling interval) --.      |          |  yyyy = measured offset,
||                                \     |          |  zzzz = estimated error.
||                                 |    |           \
MS Name/IP address         Stratum Poll Reach LastRx Last sample
===============================================================================
^* 192.0.2.026                 1   6    37     2     +2ns[  +90us] +/-   84us
=? 192.0.2.029                 2   6     1     8   +368us[ +449us] +/- 3761us
=? 192.0.2.051                 0   6     1     -     +0ns[   +0ns] +/-    0ns
=? 192.0.2.059                 2   6     1     8   +663us[ +744us] +/-   11ms

  .-- Source mode  '^' = server, '=' = peer, '#' = local clock.
/ .- Source state '*' = current best, '+' = combined, '-' = not combined,
| /             'x' = may be in error, '~' = too variable, '?' = unusable.
||                                                 .- xxxx [ yyyy ] +/- zzzz
||      Reachability register (octal) -.           |  xxxx = adjusted offset,
||      Log2(Polling interval) --.      |          |  yyyy = measured offset,
||                                \     |          |  zzzz = estimated error.
||                                 |    |           \
MS Name/IP address         Stratum Poll Reach LastRx Last sample
===============================================================================
^* 192.0.2.026                   1   6    37    29     -6ns[ -759us] +/-   92us
=? 192.0.2.029                   2   6     1    36   +334us[ -346us] +/- 3775us
=? 192.0.2.051                   2   6     1    35   -125us[ -813us] +/- 5839us
=? 192.0.2.059                   0   6     1     -     +0ns[   +0ns] +/-    0ns

  4. Verify if the chronyc in the NTP pods refers to the newly added IP.

    kubectl exec -it -n ntp-system ntp2-84ddf7cd99-96vqn -- sh

    The output looks like the following example:

    Defaulted container "ntp-image" out of: ntp-image, ntp-node-exporter
# chronyc tracking
Reference ID    : C612001E (198.18.0.30)
Stratum         : 2
Ref time (UTC)  : Wed May 21 07:28:38 2025
System time     : 0.000000005 seconds slow of NTP time
Last offset     : +0.000025645 seconds
RMS offset      : 0.000082131 seconds
Frequency       : 15.671 ppm slow
Residual freq   : +0.024 ppm
Skew            : 0.628 ppm
Root delay      : 0.000164273 seconds
Root dispersion : 0.000180630 seconds
Update interval : 64.8 seconds
Leap status     : Normal
# exit