capistranoのrole一覧をsqliteを使って取得する ref: http://qiita.com/items/bcfa059debd45257ca4b

deploy.rb

role(:server) do
  hosts = Array.new
  db = SQLite3::Database.new("serverlist.db")
  db.execute("SELECT name FROM serverlist WHERE role = 'server'") do |host|
    hosts.push(host[0])
  end
  db.close()
  hosts
end

file2.sql

CREATE TABLE serverlist (
  name varchar(10),
  env  varchar(10),
  role varchar(10)
);