capistrano_deploy_from_tag.rb

def ask_for_tag
  default_tag = `git tag`.split("\n").last
  if default_tag == nil
    puts "Please make sure you have pushed at least one tag. (git push origin --tags)"
    exit!
  else
    tag = Capistrano::CLI.ui.ask "Tag to deploy (make sure to push the tag first): [#{default_tag}] "
    tag = default_tag if tag.empty?
    tag
  end
end

namespace :deploy do
  desc "Update the deployed code."
  task :update_code, :except => { :no_release => true } do
    run "cd #{current_path}; git fetch origin; git reset --hard #{branch}"
    finalize_update
  end
end

set(:branch) { ask_for_tag }