require 'net/ssh'
require 'net/ssh/proxy/command'
require 'net/ssh/gateway'
require 'mysql2'
require 'active_record'

proxy = Net::SSH::Proxy::Command.new('ssh hgoe -W %h:%p')
option = {
  keys: ['~/.ssh/key'],
  proxy: proxy
}
gateway = Net::SSH::Gateway.new(
  'host',
  'user',
  option
)

db_connection = nil
gateway.open('rdb_host', 3306) do |local_port|
  MarioProd.establish_connection(
    adapter: 'mysql2',
    host: '127.0.0.1',
    port: local_port,
    username: 'username',
    password: 'password',
    database: 'database'
  )
  db_connection = ActiveRecord::Base.connection
end
db_connection.execute(sql)