MicroModule Outbox Bundle

Transactional Outbox Pattern bundle for reliable event delivery in event-sourced Symfony applications.

Features

• Transactional Outbox: Domain events and task commands are written to an outbox table within the same database transaction, then published asynchronously
• Broadway Integration: Optional EventStore decorator that automatically captures events to the outbox
• Dual Publishers: Separate EventPublisher (RabbitMQ) and TaskPublisher with a unified OutboxPublisher orchestrator
• OpenTelemetry Metrics: Optional counters, histograms, and gauges for outbox operations
• Feature Flag: Runtime toggle via OUTBOX_ENABLED environment variable
• Console Commands: Background publisher poller and cleanup for expired entries
• DDD Layering: Clean Domain/Infrastructure separation with interfaces

Architecture

Command Handler
    └── EventStore (wrapped by OutboxAwareEventStore)
            ├── Broadway EventStore (event persistence)
            └── OutboxRepository (outbox entry in same transaction)

Background Poller (PublishOutboxCommand)
    └── OutboxPublisher
            ├── EventPublisher → RabbitMQ
            └── TaskPublisher → Task Queue

Cleanup (CleanupOutboxCommand)
    └── OutboxRepository::deletePublishedBefore()

Installation

composer require micro-module/outbox-bundle

Register the bundle in config/bundles.php:

return [
    // ...
    MicroModule\Outbox\OutboxBundle::class => ['all' => true],
];

Configuration

# config/packages/micro_outbox.yaml
micro_outbox:
    connection: doctrine.dbal.write_connection  # DBAL connection for outbox table
    publisher:
        batch_size: 100           # Max entries per poll cycle
        poll_interval_ms: 1000    # Poll interval in milliseconds
    cleanup:
        retention_days: 30        # Days to keep published entries
        dead_letter_retention_days: 90  # Days to keep dead-letter entries
    broadway:
        enabled: true             # Enable OutboxAwareEventStore (requires broadway/broadway)
    metrics:
        enabled: false            # Enable OpenTelemetry metrics (requires open-telemetry/sdk)

Database Schema

The outbox table must be created via migration:

CREATE TABLE outbox (
    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    message_type VARCHAR(20) NOT NULL,  -- 'event' or 'task'
    payload JSONB NOT NULL,
    headers JSONB DEFAULT '{}',
    status VARCHAR(20) NOT NULL DEFAULT 'pending',
    retry_count INTEGER NOT NULL DEFAULT 0,
    max_retries INTEGER NOT NULL DEFAULT 3,
    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    published_at TIMESTAMPTZ,
    failed_at TIMESTAMPTZ,
    error_message TEXT
);

CREATE INDEX idx_outbox_status_created ON outbox (status, created_at);

Console Commands

# Publish pending outbox entries (background poller)
bin/console outbox:publish --batch-size=100 --poll-interval=1000

# Cleanup old published entries
bin/console outbox:cleanup --retention-days=30 --dead-letter-retention-days=90

Key Classes

Class	Purpose
OutboxBundle	Symfony AbstractBundle with conditional loading
OutboxEntryInterface	Domain contract for outbox entries
OutboxRepositoryInterface	Domain contract for persistence
DbalOutboxRepository	DBAL implementation of outbox storage
OutboxAwareEventStore	Broadway EventStore decorator (captures events to outbox)
OutboxAwareTaskProducer	Task producer that writes to outbox instead of direct queue
OutboxPublisher	Orchestrates EventPublisher + TaskPublisher
EventPublisher	Publishes domain events to RabbitMQ
TaskPublisher	Publishes task commands to task queue
OutboxFeatureFlag	Runtime toggle via OUTBOX_ENABLED env var
OpenTelemetryOutboxMetrics	OTel counters/histograms for monitoring
NullOutboxMetrics	No-op metrics (default when OTel disabled)

Optional Dependencies

Package	Purpose
broadway/broadway	Required for OutboxAwareEventStore and BroadwayDomainEventSerializer
micro-module/enqueue	Required for EventPublisher (RabbitMQ queue publishing)
open-telemetry/sdk	Required for OpenTelemetryOutboxMetrics

Requirements

• PHP 8.4+
• Symfony 7.0+ or 8.0+
• Doctrine DBAL 4.4+

License

Proprietary