daeltar's

Nov 30

Clockwork and delayed job and PostgreSQL

Clockwork is simple and very useful tool for scheduling tasks instead of using cron jobs in ruby.

First things first, add clockwork to your Gemfile:

gem 'clockwork'

Configuration is kept in config/clock.rb. It uses plain ruby DSL. Most amazing thing is to use custom handler which allows you to skip loading Rails environment and insert scheduled jobs directly into delyed job database table.

# Clockfile
require 'pg'
require 'yaml'
db = YAML.load_file(File.dirname(__FILE__) + "/database.yml")[ENV['RAILS_ENV'] || "development"]
conn = PGconn.connect(db['host'], nil, nil, nil, db['database'], db['username'], db['password'])

require 'clockwork'
include Clockwork


handler do |job|
  db_time = Time.now.utc.strftime("%Y-%m-%d %H:%M:%S")
  handler = "--- !ruby/object:ScheduledJob \njob: #{job}\n"
  conn.exec("INSERT INTO \"delayed_jobs\" (\"failed_at\", \"locked_by\", \"created_at\", \"handler\", \"updated_at\", \"priority\", \"run_at\", \"attempts\", \"locked_at\", \"last_error\") VALUES(NULL, NULL, '#{db_time}', '#{handler}', '#{db_time}', 0, '#{db_time}', 0, NULL, NULL)")
end

every(30.minutes, 'reactivate_paid_accounts')
# and more every blocks with definitions

And finally example of ScheduledJob:

# app/workers/scheduled_job.rb
class ScheduledJob
  attr_accessor :job
  SUPPORTED_JOBS = { 
                     :reactivate_paid_accounts    => 'Account.reactivate_paid'           
  }

  def initialize(job)
    self.job = job
    unless SUPPORTED_JOBS.has_key?(job.to_sym)
      raise "Unsupported scheduled action - #{job}"
    end
  end

  def perform
    klass, method = SUPPORTED_JOBS[job.to_sym].split('.')
    Kernel.const_get(klass).send(method.to_sym)
  end

  def display_name
    "Job/#{job}"
  end
end

Filed under // cron delayed_job postgresql ruby

Comments [0]

Jul 13

Cron tasks with style: Whenever

Whenever is simple and very useful tool for defining cron jobs in ruby.

First things first, add whenever to your Gemfile (you use bundler, right?):

gem 'whenever', :require => false

Configuration is kept in config/schedule.rb. It uses plain ruby DSL. Periodically executed code is wrapper in every blocks, in which you specify your command or rake task to be run.

It is good idea to set output redirection and disable default cron behaviour of emailing standard output (otherwise you end up with thousands local emails).

set :output, '/home/web/fakturoid/shared/log/cron.log'
env :MAILTO, "''"

Basic example can be running rake task for cleaning stale database sessions:

every 2.hours do
  rake "db:sessions:clean_nonactive"
end

I prefer application related tasks to be grouped under app namespace:

every 1.day, :at => '0:30 am' do
  rake "app:mark_as_overdue"
  rake "app:invoices_from_generators"
end

Backups should be also scheduled to run nightly:

every 1.day, :at => '2:30 am' do
  REMOTE = "someaccount@someserver.com:backups"
  rake "backup BACKUP_REMOTE=#{REMOTE}"
end

As you can see, I use rake tasks to perform scheduled jobs. But if you have background job queue system in place, it would be wise to use cron only for placing task in queue.

To generate cron configuration from ruby DSL run whenever command (via bundle exec whenever). But real fun starts with capistrano integration to regenerate cron settings after deploy. All your cron tasks will run under user specified in capistrano application variable.

# whenever.rb capistrano task
namespace :deploy do
  desc "Update the crontab file"
  task :update_crontab, :roles => :db do
    run "cd #{current_path} && /opt/ruby-enterprise/bin/bundle exec whenever --update-crontab #{application}"
  end
end
after "deploy:restart", "deploy:update_crontab"

Filed under // capistrano cron ruby whenever

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Ideas, ruby and web applications

Clockwork and delayed job and PostgreSQL

Cron tasks with style: Whenever

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