Retrying Flaky HTTP Calls with a Symfony Messenger Retry Strategy and Failure Handler

<?php

namespace App\Messenger\Retry;

use Symfony\Component\Messenger\Envelope;
use Symfony\Component\Messenger\Exception\RecoverableExceptionInterface;
use Symfony\Component\Messenger\Exception\UnrecoverableExceptionInterface;
use Symfony\Component\Messenger\Retry\RetryStrategyInterface;
use Symfony\Component\Messenger\Stamp\RedeliveryStamp;

final class ExternalCallRetryStrategy implements RetryStrategyInterface
{
    public function __construct(
        private readonly int $maxRetries = 5,
        private readonly int $delayMs = 1000,
        private readonly float $multiplier = 2.0,
        private readonly int $maxDelayMs = 60000,
    ) {
    }

    public function isRetryable(Envelope $message, ?\Throwable $throwable = null): bool
    {
        if ($throwable instanceof UnrecoverableExceptionInterface) {
            return false;
        }

        if ($throwable instanceof RecoverableExceptionInterface) {
            return true;
        }

        $retries = $this->retryCount($message);

        return $retries < $this->maxRetries;
    }

    public function getWaitingTime(Envelope $message, ?\Throwable $throwable = null): int
    {
        $retries = $this->retryCount($message);

        $delay = $this->delayMs * $this->multiplier ** $retries;
        $delay = (int) min($delay, $this->maxDelayMs);

        // Full jitter to avoid synchronized retry storms.
        return random_int((int) ($delay / 2), $delay);
    }

    private function retryCount(Envelope $message): int
    {
        $stamp = $message->last(RedeliveryStamp::class);

        return $stamp instanceof RedeliveryStamp ? $stamp->getRetryCount() : 0;
    }
}

framework:
    messenger:
        failure_transport: failed

        transports:
            async:
                dsn: '%env(MESSENGER_TRANSPORT_DSN)%'
                retry_strategy:
                    max_retries: 5
                    # Delegate backoff logic to the custom service below.
                    service: App\Messenger\Retry\ExternalCallRetryStrategy

            failed:
                dsn: 'doctrine://default?queue_name=failed'

        routing:
            App\Message\SyncCustomerMessage: async

services:
    App\Messenger\Retry\ExternalCallRetryStrategy:
        arguments:
            $maxRetries: 5
            $delayMs: 1000
            $multiplier: 2.0
            $maxDelayMs: 60000

    App\MessageHandler\SyncCustomerHandler:
        arguments:
            $crmClient: '@crm.http_client'