Example crontab generation in Capistrano

crontab.erb

# This crontab is automatically generated on deploy

SHELL=/bin/bash
[email protected]
RAILS_ENV=<%= stage %>
RAKE_CMD="<%= "#{bundle_path} rake --rakefile #{current_path}/Rakefile --trace" %>"
LOG_FILE="<%= "#{current_path}/log/cron.log" %>"

# Note: times are in the user's local time
<% if stage == :production && primary_server -%>
* * * * *  $RAKE_CMD task_for_one_host_in_production >> $LOG_FILE 2>&1
<% end -%>
<% if primary_server -%>
* * * * *  $RAKE_CMD task_for_one_host_in_all_envs   >> $LOG_FILE 2>&1
<% end -%>
* * * * *  $RAKE_CMD task_for_all_hosts_in_all_envs  >> $LOG_FILE 2>&1

deploy.rb

namespace :deploy do
  desc "Remove the remote user's crontab"
  task :remove_crontab, :roles => :app do
    run "crontab -r; true"  # ignore non-zero status when there is no crontab
  end

  desc "Generate and install crontabs"
  task :install_crontab, :roles => :app do
    bundle_path = nil
    run("which bundle", :once => true) { |_, _, output| bundle_path = output.strip }

    # generate two crontabs: one for the primary server, and one for the rest
    primary_server = true
    primary_crontab = ERB .new(File.read("lib/tasks/crontab.erb"), nil, '-').result(binding)
    primary_server = false
    app_crontab     = ERB.new(File.read("lib/tasks/crontab.erb"), nil, '-').result(binding)

    tmp_crontab_path = "#{current_path}/lib/tasks/crontab"
    put primary_crontab, tmp_crontab_path, :only => {:primary => true}
    begin
      put app_crontab,   tmp_crontab_path, :except => {:primary => true}
    rescue Capistrano::NoMatchingServersError
      puts "  * no additional app servers in this environment; skipping the non-primary crontab"
    end
    run "crontab #{tmp_crontab_path} && rm -f #{tmp_crontab_path}"
  end
end