Module: RocketJob::Plugins::Cron

Extended by:

ActiveSupport::Concern

Included in:

Jobs::HousekeepingJob

Defined in:

lib/rocket_job/plugins/cron.rb

Overview

Automatically schedules the job to start based on the supplied ‘cron_schedule`. Once started the job will automatically restart on completion and will only run again according to the `cron_schedule`. Failed jobs are aborted so that they cannot be restarted since a new instance has already been enqueued.

Include RocketJob::Plugins::Singleton to prevent multiple copies of the job from running at the same time.

Unlike cron, if a job is already running, another one is not queued when the cron schedule needs another started, but rather on completion of the current job. This prevents multiple instances of the same job from running at the same time. The next instance of the job is only scheduled on completion of the current job instance.

For example if the job takes 10 minutes to complete, and is scheduled to run every 5 minutes, it will only be run every 10 minutes.

Their is no centralized scheduler or need to start schedulers anywhere, since the jobs can be picked up by any Rocket Job worker. Once processing is complete a new instance is then automatically scheduled based on the ‘cron_schedule`.

A job is only queued to run at the specified ‘cron_schedule`, it will only run if there are workers available to run. For example if workers are busy working on higher priority jobs, then the job will only run once those jobs have completed, or their priority lowered. Additionally, while the job is queued no additional instances will be enqueued, even if the next cron interval has been reached.

Note:

• The job will not be restarted if:

  • A validation fails after cloning this job.

  • The job has expired.

Example:

class MyCronJob < RocketJob::Job

include RocketJob::Plugins::Cron

# Set the default cron_schedule
self.cron_schedule = "* 1 * * * UTC"

def perform
  puts "DONE"
end

end

# Queue the job for processing using the default cron_schedule specified above MyCronJob.create!

# Set the cron schedule: MyCronJob.create!(cron_schedule: ‘* 1 * * * America/New_York’)

Note:

To prevent multiple instances of the job from running at the same time, add: “include RocketJob::Plugins::Singleton”

Example: Only allow one instance of the cron job to run at a time:

class MyCronJob < RocketJob::Job

# Add `cron_schedule`
include RocketJob::Plugins::Cron
# Prevents mutiple instances from being queued or run at the same time
include RocketJob::Plugins::Singleton

# Set the default cron_schedule
self.cron_schedule = "* 1 * * * UTC"

def perform
  puts "DONE"
end

end

Note: The cron_schedule field is formatted as follows:

*    *    *    *    *    *
┬    ┬    ┬    ┬    ┬    ┬
│    │    │    │    │    │
│    │    │    │    │    └ Optional: Timezone, for example: 'America/New_York', 'UTC'
│    │    │    │    └───── day_of_week (0-7) (0 or 7 is Sun, or use 3-letter names)
│    │    │    └────────── month (1-12, or use 3-letter names)
│    │    └─────────────── day_of_month (1-31)
│    └──────────────────── hour (0-23)
└───────────────────────── minute (0-59)

• When specifying day of week, both day 0 and day 7 is Sunday.

• Ranges & Lists of numbers are allowed.

• Ranges or lists of names are not allowed.

• Ranges can include ‘steps’, so ‘1-9/2` is the same as `1,3,5,7,9`.

• Months or days of the week can be specified by name.

• Use the first three letters of the particular day or month (case doesn’t matter).

• The timezone is recommended to prevent any issues with possible default timezone differences across servers, or environments.