code: func (mp *MachineProvider) ack(ctx context.Context, hostname, backend string) error {
  	return mp.client.Ack(&machine.ComponentsMachineProviderRpcMessagesAckRequest{
  		Backend:  backend,
  		Hostname: hostname,
  	}).Context(ctx).Do()
  }
docs: // ack acknowledges receipt and execution of a Machine Provider instruction.