cronn - cli cron replacement and scheduler container

Use cases

• Run any job with easy to use cli scheduler
• Schedule tasks in containers (cronn can be used as CMD or ENTRYPOINT)
• Use umputun/cronn as a base image

In addition cronn provides:

• Both single-job scheduler and more traditional crontab file with multiple jobs
• Runs as an ordinary process or the entry point of a container
• Supports wide range of date templates
• Optional email notification on failed or/and passed jobs
• Optional jitter adding a random delay prior to execution of a job
• Automatic restart of jobs in cronn (or container) failed unexpectedly
• Reload crontab file on changes
• Optional repeater for failed jobs

Basic usage

• cronn -c "30 23 * * 1-5 command arg1 arg2 ..."
• cronn -c "@every 5s ls -la"
• cronn -f crontab

Scheduling can be defined as:

• standard 5-parts crontab syntax minute, hour, day-of-month, month, day-of-week
• @syntax (descriptors), like @every 5m, @midnight, @daily, @yearly, @annually, @monthly, @weekly and @hourly.

Cronn also understands various day templates evaluated at the time of job's execution:

• {{.YYYYMMDD}} - current day in local TZ
• {{.YYYY}} - current year
• {{.YYYYMM}} - year and month
• {{.ISODATE} - day-time (local TZ) formatted as 2006-01-02T00:00:00.000Z
• {{.UNIX}} - unix timestamp (in seconds)
• {{.UNIXMSEC}} - unix timestamp (in milliseconds)

Templates can be passed in the command line or crontab file and will be evaluated and replaced at the moment cronn executes the command. For example cronn "0 0 * * 1-5" echo {{.YYYYMMDD}} will print the current date every weekday on midnight.

Application Options

  -f, --file=                    crontab file (default: crontab) [$CRONN_FILE]
  -c, --command=                 crontab single command [$CRONN_COMMAND]
  -r, --resume=                  auto-resume location [$CRONN_RESUME]
  -u, --update                   auto-update mode [$CRONN_UPDATE]
  -j, --jitter                   up to 10s jitter [$CRONN_JITTER]
      --log                      enable logging [$CRONN_LOG]
      --dbg                      debug mode [$CRONN_DEBUG]

repeater:
      --repeater.attempts=       how many time repeat failed job (default: 1) [$CRONN_REPEATER_ATTEMPTS]
      --repeater.duration=       initial duration (default: 1s) [$CRONN_REPEATER_DURATION]
      --repeater.factor=         backoff factor (default: 3) [$CRONN_REPEATER_FACTOR]
      --repeater.jitter          jitter [$CRONN_REPEATER_JITTER]

notify:
      --notify.enabled-error     enable email notifications on errors [$CRONN_NOTIFY_ENABLED_ERROR]
      --notify.enabled-complete  enable completion notifications [$CRONN_NOTIFY_ENABLED_COMPLETE]
      --notify.smtp-host=        SMTP host [$CRONN_NOTIFY_SMTP_HOST]
      --notify.smtp-port=        SMTP port [$CRONN_NOTIFY_SMTP_PORT]
      --notify.smtp-username=    SMTP user name [$CRONN_NOTIFY_SMTP_USERNAME]
      --notify.smtp-password=    SMTP password [$CRONN_NOTIFY_SMTP_PASSWORD]
      --notify.smtp-tls          enable SMTP TLS [$CRONN_NOTIFY_SMTP_TLS]
      --notify.smtp-timeout=     SMTP TCP connection timeout (default: 10s) [$CRONN_NOTIFY_SMTP_TIMEOUT]
      --notify.from=             SMTP from email [$CRONN_NOTIFY_FROM]
      --notify.to=               SMTP to email(s) [$CRONN_NOTIFY_TO]
      --notify.max-log=          max number of log lines name (default: 100) [$CRONN_NOTIFY_MAX_LOG]
      --notify.host=             host name running cronn [$CRONN_NOTIFY_HOSTNAME]

Help Options:
  -h, --help                     Show this help message

Optional modes:

• Logging mode
• Debug mode: produces more debug info
• Auto-resume mode: executes terminated task(s) on startup.
• Auto-update mode: checks for changes in crontab file (-f mode only) and reloads updated jobs.

Auto-Resume details

• each task creates a flag file named as <ts>-<seq>.cronn in $CRONN_RESUME directory and removes this flag on completion.
• flag file's content is the command line for the running job.
• at the start time cronn will discover all flag files and will execute them sequentially in case if multiple flag files discovered. Note: it won't block usual, scheduled tasks and it is possible to have initial (auto-resume) task running in parallel with regular tasks.
• old resume files (>=24h) ignored
• usually it is not necessary to map $CRONN_RESUME location to host's FS as we don't want it to survive container recreation. However, it will survive container's restart.

Repeater

Optional repeater retries failed job multiple times. It uses backoff strategy with an exponential interval. Duration interval goes in steps with last * math.Pow(factor, attempt) increments. Optional jitter randomizes intervals a little bit. Factor = 1 effectively makes this strategy fixed with duration delay.

Things to know

1. CTRL-C won't kill cronn process right away but will wait till job(s) completion
2. each job runs as sh -c cmd args... to allow use of env and all other shell-related goodies

Credits

• robfig/cron for parsing and scheduling.
• pkg/errors for errors wrapping and reporting.
• jessevdk/go-flags for cli parameters parser.