A rake task to install crons

Assuming the cron tasks you want to run are stored in script/crons/{daily,hourly,monthly,weekly}/... this rake task will create the necessary crons on the system

namespace :crons do
  desc "Install the crons we need to run this site"
  task :install do
    text = ''

    template = "@%s (cd %s ; /usr/local/bin/ruby script/runner -e production script/crons/%s/%s)\n"

    Dir["#{RAILS_ROOT}/script/crons/*/*"].each do |file|
      if file =~ /crons\/daily/
        text << template % ['daily', RAILS_ROOT, 'daily', File.basename(file)]
      elsif file =~ /crons\/hourly/
        text << template % ['hourly', RAILS_ROOT, 'hourly', File.basename(file)]
      elsif file =~ /crons\/monthly/
        text << template % ['monthly', RAILS_ROOT, 'monthly', File.basename(file)]
      elsif file =~ /crons\/weekly/
        text << template % ['weekly', RAILS_ROOT, 'weekly', File.basename(file)]
      else
        puts "Unknown file #{file}"
      end
    end

    cron_file = "#{RAILS_ROOT}/script/crons/crontab.txt"

    if File.exist?(cron_file)
      File.delete(cron_file)
    end

    unless text == ''
      f = File.new(cron_file, "w")
      f.puts text
      f.close
    end
  end

  desc "Remove any previously installed crons"
  task :remove do
    cron_file = "#{RAILS_ROOT}/script/crons/crontab.txt"

    if File.exist?(cron_file)
      File.delete(cron_file)
    end
  end
end

To run it just go rake crons:install and it will create the crontabs as a text file. Then we can use the capistrano task to set them up

namespace :deploy do
  namespace :crons do
    desc "Installing the crons"
    task :install, :roles => :db do
      run "(cd #{deploy_to}/current ; rake crons:install)"
      run "cat #{deploy_to}/current/script/crons/crontab.txt | crontab -"
    end
    desc "Remove the crons"
    task :remove, :roles => :db do
      run "crontab -r"
      run "(cd #{deploy_to}/current ; rake crons:remove)"
    end
  end
end

You could probably do it all in the rake task if you wanted. You might want to set up some hooks to run this after a deploy