Errors and Monitoring in Production

// src/EventListener/ErrorContextListener.php
declare(strict_types=1);

namespace App\EventListener;

use Psr\Log\LoggerInterface;
use Symfony\Component\EventDispatcher\Attribute\AsEventListener;
use Symfony\Component\HttpKernel\Event\ExceptionEvent;
use Symfony\Component\HttpKernel\Exception\HttpExceptionInterface;

// With no arguments, the event listened to is taken from the type of the
// __invoke() argument. The longhand is a services.yaml tag naming the
// event and the method; both register the same listener.
#[AsEventListener]
final class ErrorContextListener
{
    public function __construct(private readonly LoggerInterface $logger)
    {
    }

    public function __invoke(ExceptionEvent $event): void
    {
        $throwable = $event->getThrowable();

        // An exception implementing HttpExceptionInterface carries the status
        // code it should produce. Anything else becomes a 500.
        $status = $throwable instanceof HttpExceptionInterface
            ? $throwable->getStatusCode()
            : 500;

        // A 404 is not a failure of the application. Do not page anyone.
        if ($status < 500) {
            return;
        }

        // The framework already logs the exception. This adds the fields the
        // alert query needs, and leaves the response untouched.
        $this->logger->error('Request failed', [
            'exception' => $throwable,
            'status' => $status,
            'route' => $event->getRequest()->attributes->get('_route'),
            'method' => $event->getRequest()->getMethod(),
        ]);
    }
}