protected function ensureProxy(InputInterface $input, OutputInterface $output)
    {
        // Get running containers.
        $cmd = 'docker ps';
        $process = new Process($cmd);
        $process->run();

        if (!$process->isSuccessful()) {
            throw new ProcessFailedException($process);
        }

        // Look for running instance of URL proxy in `docker ps` output.
        if (!strpos($process->getOutput(), 'jwilder/nginx-proxy')) {
            // If there's no running instance, offer to create one
            $helper = $this->getHelper('question');
            $question = new ConfirmationQuestion("URL proxy is not running, would you like to enable it now? [Y/n] ", true);
            if (!$helper->ask($input, $output, $question)) {
                $output->writeln('<error>Cancelled</error>');
            } else {
                $output->writeln('Starting URL proxy...');
                $command = $this->getApplication()->find('url-proxy:enable');
                $proxyInput = new StringInput('url-proxy:enable');
                $command->run($proxyInput, $output);
            }
        }
    }