user_index_worker.rb

class UserIndexWorker
  include TResque::Worker
  inputs :id, :first_name, :last_name, :etc

  def work
    Elasticsearch.index('users').write(id, id: id, first_name: first_name, last_name: last_name, etc: etc)
  end
end

# When user changes
UserIndexWorker.enqueue(user.attributes.slice(:id, :first_name, :last_name, :etc))