replace cron jobs with systemd timers on infra systems

[jbergstroem]

Systems running systemd can use the built in timers functionality which is intended to replace cron. The benefits (for us) using these are:

• scripts are likely more reproducible over multiple machines (read: git check in)
• easier to track:

  # systemctl list-timers --all
  NEXT                         LEFT          LAST                         PASSED    UNIT                         ACTIVA
  Sun 2017-01-08 18:45:00 UTC  4min 23s left Sun 2017-01-08 18:30:25 UTC  10min ago rsyncmirror.timer            rsyncm
  Sun 2017-01-08 21:05:36 UTC  2h 24min left Sat 2017-01-07 21:05:37 UTC  21h ago   systemd-tmpfiles-clean.timer system
  Sun 2017-01-08 22:48:09 UTC  4h 7min left  Sun 2017-01-08 08:50:37 UTC  9h ago    apt-daily.timer              apt-da
  n/a                          n/a           n/a                          n/a       ureadahead-stop.timer        ureada
  
  4 timers listed.
  

I'd like to move things we do in cron today, such as rsync:ing backups, benchmark and so on to this. Thoughts?

[jbergstroem]

Syntax btw (for above rsync script):

# tail -n +1 /etc/systemd/system/rsyncmirror.*
==> /etc/systemd/system/rsyncmirror.service <==
[Unit]
Description=runs a rsync mirror against nodejs main server

[Service]
Type=oneshot
ExecStart=/usr/bin/rsync -e "ssh" -a -q --exclude "doc" --exclude "docs" --exclude "metrics" --exclude "tools" --exclude ".*" --exclude "rsync-old-nodejs.org.sh" --exclude "www" --delete root@host:/home/dist/ /home/dist/

==> /etc/systemd/system/rsyncmirror.timer <==
[Unit]
Description=run the rsync mirror job every 15 minutes

[Timer]
OnCalendar=*:0/15

[gibfahn]

Makes sense to me if it means we can reuse scripts.

[jbergstroem]

@gibfahn said:
Makes sense to me if it means we can reuse scripts.

I guess the same applies for a checked in cron job (but os-specific things could be different).

I just really liked the tools to control timed scripts; getting full log history and confirmation that it ran successfully. It takes a bit more polish to get cron jobs to that shape.

[joaocgreis]

Syntax as listed by @jbergstroem above does not make the timer active on startup, so a reboot disables the timer. An [Install] section is required, and the timer must be explicitly enabled with systemctl enable.

Updated syntax for reference:

# tail -n +1 /etc/systemd/system/rsyncmirror.*
==> /etc/systemd/system/rsyncmirror.service <==
[Unit]
Description=runs a rsync mirror against nodejs main server

[Service]
Type=oneshot
ExecStart=/usr/bin/rsync -e "ssh" -a -q --exclude "www" --exclude "doc" --exclude "metrics" --exclude "tools" --exclude ".*" --exclude "rsync-old-nodejs.org.sh" --delete root@direct.nodejs.org:/home/dist/ /home/dist/
ExecStartPost=/usr/bin/rsync -e "ssh" -a -q --delete root@direct.nodejs.org:/home/www/ /home/www/

==> /etc/systemd/system/rsyncmirror.timer <==
[Unit]
Description=run the rsync mirror job every 15 minutes

[Timer]
OnBootSec=1min
OnUnitActiveSec=15min

[Install]
WantedBy=timers.target

Then to enable the timer:

# systemctl enable rsyncmirror.timer
Created symlink from /etc/systemd/system/timers.target.wants/rsyncmirror.timer to /etc/systemd/system/rsyncmirror.timer.

[sam-github]

Closing as stale, but if anyone wants to take this up feel free to reopen.