public function doBackground(string $jobName, string $workload) : string
    {
        try {
            $this->socket->send(json_encode([
                'action' => 'background_job',
                'job' => [
                    'name' => $jobName,
                    'workload' => $workload
                ]
            ]));
            $result = $this->socket->recv();
            return $result;
        } catch (\ZMQException $e) {
            throw new ClientException($e->getMessage());
        }
    }