Domain events are a concept used in domain-driven design (DDD). Those events are published from within a bounded context when something happened inside the domain that is relevant for other domains as well. Domain events are very useful for sharing information between separate services without establishing dedicated communication channels.

Domain events are always asynchronous - allowing to completely decouple event publisher and subscriber.

This library provides a shallow layer on top of RabbitMQ topic exchanges for publishing and receiving domain events. Publisher and subscriber need not know about each other and can be started and stopped in any order. Each subscriber controls their own retry policy, whether they need a durable queue for the time they are down, or a dead-letter queue in case there is an error in the subscriber.

Publish domain events

Events can be sent by calling publish_domain_event():

from domain_event_broker import publish_domain_event
publish_domain_event('user.registered', {'user_id':})

Domain events are sent immediately. When emitting domain events from within a database transaction, it’s recommended to defer publishing until the transaction is committed. Using a commit hook avoids spurious domain events if a transaction is rolled back after an error.

Subscribe to domain events

Subscribers can listen to one or more domain events - controlled via the binding keys. Binding keys may contain wildcards. A queue will be created for each subscriber. RabbitMQ takes care of routing only the relevant events to this queue.

This script will receive all events that are sent in the user domain:

from domain_event_broker import Subscriber

def handle_user_event(event):
    print event

subscriber = Subscriber()
subscriber.register(handle_user_event, 'print-user-event', ['user.*'])