spakky-outbox 6.4.0

Transactional Outbox pattern plugin for Spakky Framework

spakky-outbox

Transactional Outbox pattern plugin for Spakky Framework.

Installation

pip install spakky-outbox spakky-sqlalchemy

Note: spakky-outbox provides the core abstractions; spakky-sqlalchemy automatically detects and registers the Outbox storage implementation when both packages are installed.

Features

• Transactional Outbox: Events are saved atomically with business data
• Automatic relay: Background relay publishes events to external transports (Kafka, RabbitMQ)
• Retry support: Failed messages are retried with configurable limits
• Multi-instance safe: Atomic claim prevents duplicate publishing

Usage

1. Load plugins in your application

from spakky.core.application.application import SpakkyApplication
from spakky.core.application.application_context import ApplicationContext

app = (
    SpakkyApplication(ApplicationContext())
    .load_plugins()  # Loads outbox and sqlalchemy plugins automatically
    .scan()
    .start()
)

2. Publish events from use cases

Events published via IAsyncEventPublisher are automatically routed:

• AbstractDomainEvent → in-process dispatch
• AbstractIntegrationEvent → IEventBus (Outbox intercepts via @Primary)

from spakky.core.common.mutability import immutable
from spakky.core.stereotype.usecase import UseCase
from spakky.data.aspects.transactional import Transactional
from spakky.domain.models.event import AbstractIntegrationEvent
from spakky.event.event_publisher import IAsyncEventPublisher


@immutable
class OrderCreatedEvent(AbstractIntegrationEvent):
    order_id: int
    customer_id: int


@UseCase()
class CreateOrderUseCase:
    def __init__(self, event_publisher: IAsyncEventPublisher) -> None:
        self._event_publisher = event_publisher

    @Transactional()
    async def execute(self, command: CreateOrderCommand) -> Order:
        order = Order.create(...)
        # Event is saved in the same transaction as the order
        await self._event_publisher.publish(
            OrderCreatedEvent(order_id=order.id, customer_id=command.customer_id)
        )
        return order

3. Configure via environment variables

Variable	Default	Description
SPAKKY_OUTBOX__POLLING_INTERVAL_SECONDS	1.0	Relay polling interval
SPAKKY_OUTBOX__BATCH_SIZE	100	Messages per batch
SPAKKY_OUTBOX__MAX_RETRY_COUNT	5	Max retries before giving up
SPAKKY_OUTBOX__CLAIM_TIMEOUT_SECONDS	300.0	Claim expiry for crash recovery

Components

Component	Description
IOutboxStorage / IAsyncOutboxStorage	Outbox message storage port
OutboxEventBus / AsyncOutboxEventBus	Event bus seam for Outbox pattern (@Primary replaces DirectEventBus)
OutboxRelayBackgroundService / AsyncOutboxRelayBackgroundService	Background relay service (polls & sends)
OutboxConfig	Configuration via environment variables
OutboxMessage	Outbox message model

Custom Storage Implementation

To implement a custom storage backend:

from spakky.outbox.ports.storage import IAsyncOutboxStorage
from spakky.outbox.common.message import OutboxMessage

class MyCustomStorage(IAsyncOutboxStorage):
    async def save(self, message: OutboxMessage) -> None:
        # Save within the current transaction
        ...

    async def fetch_pending(self, limit: int, max_retry: int) -> list[OutboxMessage]:
        # Atomic claim and return pending messages
        ...

    async def mark_published(self, message_id: UUID) -> None:
        ...

    async def increment_retry(self, message_id: UUID) -> None:
        ...

License

MIT License