castle-cron is a distributed time-based job scheduler similar to cron. It supports a CLI for maintaining a list of jobs and runs them at the appropriate time on one of its servers (chosen randomly). It is highly available and supports any number of servers. Servers can enter or leave the cluster at any time. The system can survive process, machine and data center failures and will continue to function as long as at least one server is running.
There is one executable that supports both the CLI and the server, depending on invocation arguments. The system requires and uses Zookeeper, which it uses to store and manage its job list, and to report on server availability.
castle-cron -s [-zk Zookeeper server(s)] [-zt timeout] [-n name] [-f] [-v]
Invokes castle-cron as a server daemon logging to the console. It connects to the designated Zookeeper server and waits for the scheduled start time of the next job or for a schedule change. Once the scheduled time arrives, it competes with other servers for the right to run the job, and if successful, runs the job. It then returns to the wait.
You can start any number of castle-cron servers. Each server's console log reports when other servers enter or depart the cluster. Scheduled jobs are assigned to a server at random from the servers available at the time the job runs.
| Argument | Default | Significance |
|---|---|---|
| -s | Required. Indicates castle-cron should run as a server | |
| -zk | ZOOKEEPER_SERVERS | Optional; if omitted, the value must be supplied in the ZOOKEEPER_SERVERS environment variable. Specifies a comma-separated list of servers in the form hostname:port[,hostname:port...] |
| -zt | 10 | Zookeeper timeout. Specifies the number of seconds of non-contact before a session times out. |
| -n | hostname | Server name. Can include %h (hostname) and %p (pid). |
| -f | Force start. Start the server even if its name duplicates another server. | |
| -v | Verbose. Include TRACE logging. |
castle-cron [-zk Zookeeper server(s)] [-zt timeout] [-v] add jobname schedule cmd args
castle-cron [-zk Zookeeper server(s)] [-zt timeout] [-v] upd jobname schedule cmd args
castle-cron [-zk Zookeeper server(s)] [-zt timeout] [-v] del jobname
castle-cron [-zk Zookeeper server(s)] [-zt timeout] [-v] list [jobname]
castle-cron [-zk Zookeeper server(s)] [-zt timeout] [-v] help add|del|upd|list|sched
Maintains the job list. All jobs must have a unique name, but are otherwise specified in a similar format to jobs in crontab. CLI commands available are:
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add Adds a new job. The schedule is a has a similar format to cron; see below.
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upd Updates an existing job. All arguments must be provided.
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del Deletes a job.
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list Lists all or a subset of jobs. The optional jobname argument can asterisk as a wildcard character (matching one or more characters). If jobname is omitted, list shows all jobs.
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help Shows help for CLI commands. help sched describes the format of the schedule argument of add and upd
Job schedule; must be a quoted string containing 5 - 7 blank-separated values. Field name Mandatory? Allowed values Allowed special characters ---------- ---------- -------------- -------------------------- Seconds No 0-59 * / , - Minutes Yes 0-59 * / , - Hours Yes 0-23 * / , - Day of month Yes 1-31 * / , - L W Month Yes 1-12 or JAN-DEC * / , - Day of week Yes 0-6 or SUN-SAT * / , - L # Year No 1970–2099 * / , -