Introduction¶ ↑
Whenever is a Ruby gem that provides a clear syntax for defining cron jobs. It outputs valid cron syntax and can even write your crontab file for you. It is designed to work well with Rails applications and can be deployed with Capistrano. Whenever works fine independently as well.
Ryan Bates created a great Railscast about Whenever: railscasts.com/episodes/164-cron-in-ruby
Discussion: groups.google.com/group/whenever-gem
Installation¶ ↑
If you haven’t already, get set up with gemcutter.org
$ sudo gem install whenever
In a Rails (2.1 or greater) application:
in your “config/environment.rb” file:
Rails::Initializer.run do |config| config.gem 'whenever', :lib => false, :source => 'http://gemcutter.org/' end
Getting started¶ ↑
$ cd /my/rails/app $ wheneverize .
This will create an initial “config/schedule.rb” file you.
Example schedule.rb file¶ ↑
every 3.hours do runner "MyModel.some_process" rake "my:rake:task" command "/usr/bin/my_great_command" end every 1.day, :at => '4:30 am' do runner "MyModel.task_to_run_at_four_thirty_in_the_morning" end every :hour do # Many shortcuts available: :hour, :day, :month, :year, :reboot runner "SomeModel.ladeeda" end every :sunday, :at => '12pm' do # Use any day of the week or :weekend, :weekday runner "Task.do_something_great" end
More examples on the wiki: wiki.github.com/javan/whenever/instructions-and-examples
Cron output¶ ↑
$ cd /my/rails/app $ whenever
And you’ll see your schedule.rb converted to cron sytax. Note: running ‘whenever’ with no options does not display your current crontab file, it simply shows you the output of converting your schedule.rb file.
Capistrano integration¶ ↑
In your “config/deploy.rb” file do something like:
after "deploy:symlink", "deploy:update_crontab" namespace :deploy do desc "Update the crontab file" task :update_crontab, :roles => :db do run "cd #{release_path} && whenever --update-crontab #{application}" end end
This will update your crontab file, leaving any existing entries unharmed. When using the --update-crontab
option, Whenever will only update the entries in your crontab file related to the current schedule.rb file. You can replace the #{application}
with any identifying string you’d like. You can have any number of apps deploy to the same crontab file peacefully given they each use a different identifier.
If you wish to simply overwrite your crontab file each time you deploy, use the --write-crontab
option. This is ideal if you are only working with one app and every crontab entry is contained in a single schedule.rb file.
By mixing and matching the --load-file
and --user
options with your various :roles in Capistrano it is entirely possible to deploy different crontab schedules under different users to all your various servers. Get creative!
If you want to override a variable (like your environment) at the time of deployment you can do so with the --set
option: wiki.github.com/javan/whenever/setting-variables-on-the-fly
Credit¶ ↑
Whenever was created for use at Inkling (inklingmarkets.com) where I work. Their take on it: blog.inklingmarkets.com/2009/02/whenever-easy-way-to-do-cron-jobs-from.html
While building Whenever, I learned a lot by digging through the source code of Capistrano - github.com/jamis/capistrano
Discussion / Feedback / Issues / Bugs¶ ↑
For general discussion and questions, please use the google group: groups.google.com/group/whenever-gem
If you’ve found a genuine bug or issue, please use the Issues section on github: github.com/javan/whenever/issues
License¶ ↑
Copyright © 2009 Javan Makhmali
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.