Net::SSH.start(ip, 'ubuntu', keys: "mykey.pem" ) do |ssh|
  ssh.exec "sudo chmod +x /tmp/provision.sh"
end

model Instance

  def chmod
    start do |ssh|
      ssh.exec "sudo chmod +x /tmp/provision.sh"
      # other operations on ssh
    end
  end

  private

    def start
      Net::SSH.start(ip, 'ubuntu', keys: "mykey.pem" ) do |ssh|
        yield ssh
      end
    end
end