PHPOutbox — Transactional Outbox for PHP

Stop losing events. PHPOutbox implements the Transactional Outbox Pattern for PHP — guaranteed at-least-once event delivery for Laravel, Symfony, and vanilla PHP applications.

The Problem

// ❌ DANGEROUS — dual-write problem
DB::transaction(function () use ($order) {
    $order->save();
});
// If the app crashes here, or the queue is down...
event(new OrderCreated($order));  // 💀 Event lost forever

The Solution

// ✅ SAFE — atomic outbox write
DB::transaction(function () use ($order) {
    $order->save();
    Outbox::store('Order', $order->id, 'OrderCreated', $order->toArray());
    // Both written in the SAME transaction — both succeed or both fail
});

// Background relay publishes to your queue — guaranteed delivery
// php artisan outbox:relay

Features

• Atomic writes — Events stored in the same DB transaction as business data
• Background relay — Polls outbox table, publishes to your queue
• Retry with backoff — Failed publishes retry automatically
• Dead letter queue — Messages moved to dead-letter after max retries
• Concurrent workers — Multiple relays via SELECT FOR UPDATE SKIP LOCKED
• Framework-agnostic — Core works with raw PDO, zero framework deps
• Laravel adapter — ServiceProvider, Facade, Artisan commands
• Symfony adapter — Bundle, Console commands, Messenger integration
• Observability — PSR-3 logging, relay metrics per cycle
• Housekeeping — Auto-prune old messages

Requirements

• PHP 8.2+
• MySQL 8.0+ or PostgreSQL 9.5+ (SQLite for testing)
• PDO extension

Installation

composer require sumantasam1990/phpoutbox

Quick Start

Laravel

1. Publish config:

php artisan vendor:publish --tag=outbox-config

2. Create the outbox table:

php artisan outbox:migrate

3. Store events (inside your DB transaction):

use PhpOutbox\Outbox\Laravel\Facades\Outbox;
use Illuminate\Support\Facades\DB;

DB::transaction(function () {
    $order = Order::create([
        'customer_id' => 42,
        'total' => 199.99,
    ]);

    Outbox::store(
        aggregateType: 'Order',
        aggregateId: (string) $order->id,
        eventType: 'OrderCreated',
        payload: $order->toArray(),
        headers: ['correlation-id' => request()->header('X-Correlation-ID')],
    );
});

4. Run the relay daemon:

php artisan outbox:relay

Or for cron-based relay:

php artisan outbox:relay --once

5. Schedule pruning in routes/console.php:

Schedule::command('outbox:prune --days=30')->daily();

Symfony

1. Register the bundle:

// config/bundles.php
return [
    // ...
    PhpOutbox\Outbox\Symfony\OutboxBundle::class => ['all' => true],
];

2. Configure:

# config/packages/outbox.yaml
outbox:
    table_name: outbox_messages
    relay:
        batch_size: 100
        poll_interval_ms: 1000
        max_attempts: 5

3. Run the relay:

bin/console outbox:relay

Vanilla PHP (No Framework)

use PhpOutbox\Outbox\Outbox;
use PhpOutbox\Outbox\OutboxConfig;
use PhpOutbox\Outbox\Store\PdoOutboxStore;
use PhpOutbox\Outbox\Store\Schema;
use PhpOutbox\Outbox\Relay\OutboxRelay;

// Setup
$pdo = new PDO('mysql:host=localhost;dbname=myapp', 'user', 'pass');
$config = new OutboxConfig(batchSize: 50, maxAttempts: 3);
$store = new PdoOutboxStore($pdo, $config);
$outbox = new Outbox($store);

// Create table (one-time)
$pdo->exec(Schema::mysql());

// Store an event (inside your transaction)
$pdo->beginTransaction();
$pdo->exec("INSERT INTO orders (id, total) VALUES (1, 99.99)");
$outbox->store('Order', '1', 'OrderCreated', ['total' => 99.99]);
$pdo->commit();

// Run relay (implement OutboxPublisher for your broker)
$publisher = new MyRabbitMQPublisher();
$relay = new OutboxRelay($store, $publisher, $config);
$relay->run(); // Blocks forever — run in a supervisor

Configuration

Laravel Config (config/outbox.php)

Key	Env Variable	Default	Description
table_name	OUTBOX_TABLE	outbox_messages	Outbox table name
connection	OUTBOX_CONNECTION	null (default)	Database connection
relay.batch_size	OUTBOX_BATCH_SIZE	100	Messages per relay cycle
relay.poll_interval_ms	OUTBOX_POLL_INTERVAL	1000	Ms between polls
relay.max_attempts	OUTBOX_MAX_ATTEMPTS	5	Max retries before dead-letter
publisher.queue_connection	OUTBOX_QUEUE_CONNECTION	null	Queue connection
publisher.queue_name	OUTBOX_QUEUE_NAME	outbox	Queue name
prune_after_days	OUTBOX_PRUNE_DAYS	30	Days to keep published messages
delete_on_publish	OUTBOX_DELETE_ON_PUBLISH	false	Delete vs mark as published
id_generator	OUTBOX_ID_GENERATOR	uuid7	ID strategy: uuid7 or ulid

Custom Publisher

Implement OutboxPublisher for your message broker:

use PhpOutbox\Outbox\Contracts\OutboxPublisher;
use PhpOutbox\Outbox\Exception\PublishException;
use PhpOutbox\Outbox\Message\OutboxMessage;

class RabbitMQPublisher implements OutboxPublisher
{
    public function __construct(private AMQPChannel $channel) {}

    public function publish(OutboxMessage $message): void
    {
        try {
            $this->channel->basic_publish(
                new AMQPMessage($message->payload),
                'events',
                $message->eventType,
            );
        } catch (\Throwable $e) {
            throw PublishException::failed($message->id, $e);
        }
    }

    public function publishBatch(array $messages): void
    {
        foreach ($messages as $message) {
            $this->publish($message);
        }
    }
}

Monitoring

The relay returns metrics per cycle:

$metrics = $relay->runOnce();

echo $metrics->summary();
// "Cycle #42: 100 processed (98 published, 1 failed, 1 dead-lettered) in 45.2ms"

$metrics->processed;    // Total messages handled
$metrics->published;    // Successfully published
$metrics->failed;       // Failed (will retry)
$metrics->deadLettered; // Exhausted retries
$metrics->durationMs;   // Cycle duration

Architecture

See docs/ARCHITECTURE.md for detailed flow diagrams, concurrency model, and extension points.

Testing

# All tests
./vendor/bin/phpunit

# Unit tests only
./vendor/bin/phpunit --testsuite=unit

# Integration tests (SQLite in-memory)
./vendor/bin/phpunit --testsuite=integration

# Static analysis
./vendor/bin/phpstan analyse

Contributing

Contributions are welcome! Please read our Contributing Guide for details on our code of conduct, how to submit pull requests, and our development process.

1. Fork the repository
2. Create a feature branch
3. Write tests for your changes
4. Ensure all tests pass and PHPStan is clean
5. Submit a pull request

License

MIT License. See LICENSE for details.