[Bug 1749722] Re: NTP: take into account systemd-timesyncd where present

[Ryan Harper]

Some further looking at the systemd side, Bionic no longer carries the
override conf (disable-with-time-daemon.conf) in favor of updating each
client's systemd unit to use:

Conflicts=systemd-timesyncd.service

Conflicts will ensure that the target service is stopped if the current
unit is started. So, if ntp or chrony unit were to start, it would stop
timesyncd.

This is roughly equivalent, however, it does leave timesyncd unit
enabled.  This means that if something starts systemd-timesyncd.service,
it would stop the ntp or chrony service.

There may be additional work on each of the time packages to *disable*
timesyncd unit when installed such that it won't start.  This may not be
possible to prevent users from starting timesyncd manually.

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https://bugs.launchpad.net/bugs/1749722

Title:
  NTP: take into account systemd-timesyncd where present

Status in cloud-init:
  In Progress
Status in systemd package in Ubuntu:
  New

Bug description:
  Currently, the NTP module configures ntpd during cloud-init install by
  installing and configuring ntpd.

  ntpd competes with systemd-timesyncd on systemd distros like Ubuntu
  Xenial.

  Ideally the NTP module should configure systemd-timesyncd where
  present, falling back to ntpd where not present.

  This stops two separate daemons (ntpd and systemd-timesyncd) competing
  with each other to set the time, where systemd-timesyncd (on Ubuntu at
  least) has an internal hardcoded compiled in timeserver to fall back
  on if no timeserver is configured (which is bad, but what can you do).

  The competing timeserver behaviour is invisible when the machine can
  see the net, but logs this error constantly when the machine cannot
  see the net:

  systemd-timesyncd[527]: Timed out waiting for reply from
  91.189.94.4:123 (ntp.ubuntu.com).

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