Whenever is a Ruby gem that provides a clear syntax for writing and deploying cron jobs.
Installation
$ gem install whenever
Or with Bundler in your Gemfile.
gem 'whenever', :require => false
Getting started
$ cd /apps/my-great-project
$ wheneverize .
This will create an initial config/schedule.rb
file for 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
every '0 0 27-31 * *' do
command "echo 'you can use raw cron syntax too'"
end
# run this task only on servers with the :app role in Capistrano
# see Capistrano roles section below
every :day, :at => '12:20am', :roles => [:app] do
rake "app_server:task"
end
Define your own job types
Whenever ships with three pre-defined job types: command, runner, and rake. You can define your own with job_type
.
For example:
job_type :awesome, '/usr/local/bin/awesome :task :fun_level'
every 2.hours do
awesome "party", :fun_level => "extreme"
end
Would run /usr/local/bin/awesome party extreme
every two hours. :task
is always replaced with the first argument, and any additional :whatevers
are replaced with the options passed in or by variables that have been defined with set
.
The default job types that ship with Whenever are defined like so:
job_type :command, ":task :output"
job_type :rake, "cd :path && :environment_variable=:environment bundle exec rake :task --silent :output"
job_type :runner, "cd :path && script/rails runner -e :environment ':task' :output"
job_type :script, "cd :path && :environment_variable=:environment bundle exec script/:task :output"
Pre-Rails 3 apps and apps that don't use Bundler will redefine the rake
and runner
jobs respectively to function correctly.
If a :path
is not set it will default to the directory in which whenever
was executed. :environment_variable
will default to 'RAILS_ENV'. :environment
will default to 'production'. :output
will be replaced with your output redirection settings which you can read more about here: http://github.com/javan/whenever/wiki/Output-redirection-aka-logging-your-cron-jobs
All jobs are by default run with bash -l -c 'command...'
. Among other things, this allows your cron jobs to play nice with RVM by loading the entire environment instead of cron's somewhat limited environment. Read more: http://blog.scoutapp.com/articles/2010/09/07/rvm-and-cron-in-production
You can change this by setting your own :job_template
.
set :job_template, "bash -l -c ':job'"
Or set the job_template to nil to have your jobs execute normally.
set :job_template, nil
Capistrano integration
Use the built-in Capistrano recipe for easy crontab updates with deploys. For Capistrano V3, see the next section.
In your "config/deploy.rb" file:
require "whenever/capistrano"
Take a look at the recipe for options you can set. https://github.com/javan/whenever/blob/master/lib/whenever/capistrano/v2/recipes.rb For example, if you're using bundler do this:
set :whenever_command, "bundle exec whenever"
require "whenever/capistrano"
If you are using different environments (such as staging, production), then you may want to do this:
set :whenever_environment, defer { stage }
require "whenever/capistrano"
The capistrano variable :stage
should be the one holding your environment name. This will make the correct :environment
available in your schedule.rb
.
If both your environments are on the same server you'll want to namespace them or they'll overwrite each other when you deploy:
set :whenever_environment, defer { stage }
set :whenever_identifier, defer { "#{application}_#{stage}" }
require "whenever/capistrano"
Capistrano V3 Integration
In your "Capfile" file:
require "whenever/capistrano"
Take a look at the load:defaults (bottom of file) task for options you can set. http://github.com/javan/whenever/blob/master/lib/whenever/tasks/whenever.rake. For example, to namespace the crontab entries by application and stage do this.
set :whenever_identifier, ->{ "#{fetch(:application)}_#{fetch(:stage)}" }
Capistrano roles
The first thing to know about the new roles support is that it is entirely optional and backwards-compatible. If you don't need different jobs running on different servers in your capistrano deployment, then you can safely stop reading now and everything should just work the same way it always has.
When you define a job in your schedule.rb file, by default it will be deployed to all servers in the whenever_roles list (which defaults to [:db]).
However, if you want to restrict certain jobs to only run on subset of servers, you can add a :roles => [...] argument to their definitions. Make sure to add that role to the whenever_roles list in your deploy.rb.
When you run cap deploy
, jobs with a :roles list specified will only be added to
the crontabs on servers with one or more of the roles in that list.
Jobs with no :roles argument will be deployed to all servers in the whenever_roles list. This is to maintain backward compatibility with previous releases of whenever.
So, for example, with the default whenever_roles of [:db], a job like this would be deployed to all servers with the :db role:
every :day, :at => '12:20am' do
rake 'foo:bar'
end
If we set whenever_roles to [:db, :app] in deploy.rb, and have the following jobs in schedule.rb:
every :day, :at => '1:37pm', :roles => [:app] do
rake 'app:task' # will only be added to crontabs of :app servers
end
every :hour, :roles => [:db] do
rake 'db:task' # will only be added to crontabs of :db servers
end
every :day, :at => '12:02am' do
command "run_this_everywhere" # will be deployed to :db and :app servers
end
Here are the basic rules:
- If a server's role isn't listed in whenever_roles, it will never have jobs added to its crontab.
- If a server's role is listed in the whenever_roles, then it will have all jobs added to its crontab that either list that role in their :roles arg or that don't have a :roles arg.
- If a job has a :roles arg but that role isn't in the whenever_roles list, that job will not be deployed to any server.
RVM Integration
If your production environment uses RVM (Ruby Version Manager) you will run into a gotcha that causes your cron jobs to hang. This is not directly related to Whenever, and can be tricky to debug. Your .rvmrc files must be trusted or else the cron jobs will hang waiting for the file to be trusted. A solution is to disable the prompt by adding this line to your user rvm file in ~/.rvmrc
rvm_trust_rvmrcs_flag=1
This tells rvm to trust all rvmrc files.
whenever
command
The $ cd /apps/my-great-project
$ whenever
This will simply show you your schedule.rb
file converted to cron syntax. It does not read or write your crontab file. Run whenever --help
for a complete list of options.
Credit
Whenever was created for use at Inkling (http://inklingmarkets.com). Their take on it: http://blog.inklingmarkets.com/2009/02/whenever-easy-way-to-do-cron-jobs-from.html
Thanks to all the contributors who have made it even better: http://github.com/javan/whenever/contributors
Discussion / Feedback / Issues / Bugs
For general discussion and questions, please use the google group: http://groups.google.com/group/whenever-gem
If you've found a genuine bug or issue, please use the Issues section on github: http://github.com/javan/whenever/issues
Ryan Bates created a great Railscast about Whenever: http://railscasts.com/episodes/164-cron-in-ruby It's a little bit dated now, but remains a good introduction.
Compatible with Ruby 1.8.7-2.1.0, JRuby, and Rubinius.
Copyright © 2014 Javan Makhmali