Capistrano Mongoid recipes

gistfile1.rb

# Use the config/mongoid/#{rails_env}.yml file for mongoid config

namespace :mongoid do
  desc "Copy mongoid config"
  task :copy do
    upload "config/mongoid/#{rails_env}.yml", "#{shared_path}/mongoid.yml", :via => :scp
  end

  desc "Link the mongoid config in the release_path"
  task :symlink do
    run "test -f #{release_path}/config/mongoid.yml || ln -s #{shared_path}/mongoid.yml #{release_path}/config/mongoid.yml"
  end

  desc "Create MongoDB indexes"
  task :index do
    run "cd #{current_path} && #{bundle_cmd} exec rake db:mongoid:create_indexes", :once => true
  end
end

after "deploy:update_code", "mongoid:copy"
after "deploy:update_code", "mongoid:symlink"
after "deploy:update", "mongoid:index"

Hey @voldy! Could you please help me a bit with this code?
What does it exactly mean :once => true? As we actually need to create indexes on each deploy (it's like a migration).
Also is #{bundle_cmd} still relevant? Does it have a RAILS_ENV variable setting inside of it?