crono

Job scheduler for Rails

Crono is a time-based background job scheduler daemon (just like Cron) for Ruby on Rails.

The Purpose

Currently, there is no such thing as Ruby Cron for Rails. Well, there’s Whenever but it works on top of Unix Cron, so you can’t manage it from Ruby. Crono is pure Ruby. It doesn’t use Unix Cron and other platform-dependent things. So you can use it on all platforms supported by Ruby. It persists job states to your database using Active Record. You have full control of jobs performing process. It’s Ruby, so you can understand and modify it to fit your needs.

Installation

Add the following line to your application’s Gemfile:

gem 'crono'

Run the bundle command to install it.
After you install Crono, you can run the generator:

rails generate crono:install

It will create a configuration file config/cronotab.rb and migration
Run the migration:

rake db:migrate

Now you are ready to move forward to create a job and schedule it.

Compatibility

• Crono v1.1.2 and older are compatible with Ruby 2.7.x and older
• Crono v2.0.0 and newer are compatible with Ruby 2.7.x and newer

Usage

The basic usage

You can specify a simple job by editing config/cronotab.rb:

# config/cronotab.rb
class TestJob
  def perform
    puts 'Test!'
  end
end

Crono.perform(TestJob).every 5.seconds

Then, run a crono process:

bundle exec crono -e development

Job Schedule

Schedule list is defined in the file config/cronotab.rb, that created using rake crono:install. The semantic is pretty straightforward:

# config/cronotab.rb
Crono.perform(TestJob).every 2.days, at: {hour: 15, min: 30}
Crono.perform(TestJob).every 1.week, on: :monday, at: "15:30"

You can schedule one job a few times if you want the job to be performed a few times a day or a week:

Crono.perform(TestJob).every 1.week, on: :monday
Crono.perform(TestJob).every 1.week, on: :thursday

The at can be a Hash:

Crono.perform(TestJob).every 1.day, at: {hour: 12, min: 15}

You can schedule a job with arguments, which can contain objects that can be serialized using JSON.generate

Crono.perform(TestJob, 'some', 'args').every 1.day, at: {hour: 12, min: 15}

You can set some options that not passed to the job but affect how the job will be treated by Crono. For example, you can set to truncate job logs (which stored in the database) to a certain number of records:

Crono.perform(TestJob).with_options(truncate_log: 100).every 1.week, on: :monday

Job classes

Crono can use Active Job jobs from app/jobs/. Here’s an example of a job:

# app/jobs/test_job.rb
class TestJob < ActiveJob::Base
  def perform(options)
    # put you scheduled code here
    # Comments.deleted.clean_up...
  end
end

The ActiveJob jobs are convenient because you can use one job in both periodic and enqueued ways. But Active Job is not required. Any class can be used as a crono job if it implements a method perform:

class TestJob # This is not an Active Job job, but pretty legal Crono job.
  def perform(*args)
    # put you scheduled code here
    # Comments.deleted.clean_up...
  end
end

Run rake tasks

Here’s an example of a Rake Task within a job:

# config/cronotab.rb
require 'rake'

Rails.app_class.load_tasks

class Test
  def perform
    Rake::Task['crono:hello'].execute
  end
end

Crono.perform(Test).every 5.seconds

With the rake task of:

# lib/tasks/test.rake
namespace :crono do
  desc 'Update all tables'
  task :hello => :environment do
    puts "hello"
  end
end

Please note that crono uses threads, so your code should be thread-safe

Run crono

Run crono in your Rails project root directory:

bundle exec crono -e development

Usage:

Usage: crono [options] [start|stop|restart|run]
    -C, --cronotab PATH              Path to cronotab file (Default: config/cronotab.rb)
    -L, --logfile PATH               Path to writable logfile (Default: log/crono.log)
    -P, --pidfile PATH               Deprecated! use --piddir with --process_name; Path to pidfile (Default: )
    -D, --piddir PATH                Path to piddir (Default: tmp/pids)
    -N, --process_name NAME          Name of the process (Default: crono)
    -m, --monitor                    Start monitor process for a deamon (Default false)
    -e, --environment ENV            Application environment (Default: development)

Run as a daemon

To run Crono as a daemon, please add to your Gemfile:

gem 'daemons'

Then:

bundle install; bundle exec crono start RAILS_ENV=development

There are “start”, “stop”, and “restart” commands.

Web UI

Crono can display the current state of Crono jobs.

Add the following to your config/routes.rb:

Rails.application.routes.draw do
    mount Crono::Engine, at: '/crono'
    ...

Access management and other questions described in the wiki.

Known issues

For Rails 5, in case of the errors:

`require': cannot load such file -- rack/showexceptions (LoadError)

See the related issue #52

Capistrano

Use the capistrano-crono gem (github).

Development

Running tests

To run the tests, you need to have a database. You can use the default SQLite database:

bundle exec rspec

Publishing

To publish a new version, you need to update the version number in lib/crono/version.rb and then run:

bundle exec rake release

Support

Feel free to create an issues

License

Please see LICENSE for licensing details.