a.rb

require 'rubygems'
require 'ruote'
require 'ruote/storage/fs_storage'

engine = Ruote::Engine.new(
  Ruote::Worker.new(
    Ruote::FsStorage.new('work')))

pdef = Ruote.define do
  concurrent-iterator :on_f => 'ips', :to_f => 'ip', :merge_type => 'concat' do
    ssh :ip => '${ip}', :command => 'du -f'
  end
  emit_results
end

engine.register 'ssh', Taz::SshParticipant
engine.register 'emit_results', Taz::ResultParticipant

# ...

wfid = engine.launch(pdef, 'ips' => %w[ 192.168.1.1 192.168.1.2 192.168.1.3 ])