Bad user experience

Security

CVE-2019-11037 - my bad

  push graphic-context
  viewbox 0 0 640 480
  fill 'url(https://example.com/image.jpg"|ls "-la)'
  pop graphic-context

  // Upload as .mvg file

Demo time

Components

• Job/message queue
• Some code to send/receive the jobs
• Something to keep the code running
• Some code to stop the jobs

Some code to send the jobs

class ImageJob {

    /** @var string */
    private $text;

    function __construct(string $text) {
        $this->text = $text;
    }

    public function toString(): string {
        $data = ['text' => $this->text];

        return json_encode_safe($data);
    }

    public function getText(): string {
      return $this->text;
    }

    public static function fromString(string $string) {
        $data = json_decode_safe($string);
        return new self($data['text']);
    }
}

Some code to send the jobs

class RedisImageJobRepo {

    public function queueImageJob(ImageJob $imageJob)
    {
        $this->redis->rpush(
            ImageJobKey::getAbsoluteKeyName(),
            $imageJob->toString()
        );
        return true;
    }
}

Some code to retrieve the jobs

class RedisImageJobRepo
{
    function waitForImageJob(int $timeout = 5): ?ImageJob {
        $key = ImageJobKey::getAbsoluteKeyName();

        // Next line sits and waits for a job
        $listElement = $this->redis->blpop([$key], $timeout);
        if (count($listElement) === 0) {
            return null;
        }

        $keyReturned = $listElement[0];
        $data = $listElement[1];

        $imageJob = ImageJob::fromString($data);

        return $imageJob;
    }
}

Code for encapsulating keys

class ImageJobKey {
  static function getAbsoluteKeyName() : string {
    return str_replace('\\', '', __CLASS__);
  }

  static function getKeyNameForStatus(string $jobId): string {
    return str_replace('\\', '', __CLASS__) .
      ':status:' . $jobId;
  }
}

Supervisord config

[program:image_generator]
directory=/var/www
command=php cli.php process:image_example
process_name=%(program_name)s_%(process_num)d
user=www-data
numprocs=1
autostart=true
autorestart=true

# also boring log file stuff...

Emails: 4 GB / 16 MB per worker

256 workers
* 8 business hours a day
* 5 days a week
* 4 weeks a month
* 3600 seconds in an hour
/ 4 seconds to send an email

= 36,864,000 emails a month

</rant>

Code to run in a loop

function continuallyExecuteCallable($callable, int $maxRunTime)
{
    $startTime = microtime(true);
    while (true) {
        $callable();
        if (checkSignalsForExit()) {
            break;
        }

        if ((microtime(true) - $startTime) > $maxRunTime) {
            break;
        }
    }
}

Make code run in a loop

• Avoid DOS your own system
• Avoid DOS other people's system
• Avoid spinning your CPU at 100%

Some code to stop the jobs

aka listen to signals.

• SIGINT - Ctrl+C
• SIGTERM - graceful shut down
• SIGKILL - ungraceful

“Upon the receival of the SIGTERM, each container should start a graceful shutdown of the running application and exit.” “If a container doesn’t terminate within the grace period, a SIGKILL signal will be sent and the container violently terminated.”

Other benefits

• Disable background workers when service is down
• Retrying failed jobs
• Performance tuning
• Performance monitoring and scaling
• Use different language