A broker agnostic implementation of the outbox and other message resilience patterns for Django apps.
To use jaiminho with your project, you just need to do 6 steps:
python -m pip install jaiminhoINSTALLED_APPS = [
...
"jaiminho"
]python manage.py migrateJAIMINHO_CONFIG = {
"PERSIST_ALL_EVENTS": False,
"DELETE_AFTER_SEND": True,
"DEFAULT_ENCODER": DjangoJSONEncoder,
"PUBLISH_STRATEGY": "publish-on-commit",
}from jaiminho.send import save_to_outbox
@save_to_outbox
def any_external_call(**kwargs):
# do something
returnpython manage.py events_relay --run-in-loop --loop-interval 1
If you don't use --run-in-loop option, the relay command will run only 1 time. This is useful in case you want to configure it as a cronjob.
Jaiminho @save_to_outbox decorator will intercept decorated function and persist it in a database table in the same transaction that is active in the decorated function context. The event relay command, is a separated process that fetches the rows from this table and execute the functions. When an outage happens, the event relay command will keep retrying until it succeeds. This way, eventual consistency is ensured by design.
PUBLISH_STRATEGY- Strategy used to publish events (publish-on-commit, keep-order)PERSIST_ALL_EVENTS- Saves all events and not only the ones that fail, default isFalse. Only applicable for{ "PUBLISH_STRATEGY": "publish-on-commit" }since all events needs to be stored on keep-order strategy.DELETE_AFTER_SEND- Delete the event from the outbox table immediately, after a successful sendDEFAULT_ENCODER- Default Encoder for the payload (overwritable in the function call)
This strategy is similar to transactional outbox described by Chris Richardson. The decorated function intercepts the function call and saves it on the local DB to be executed later. A separate command relayer will keep polling local DB and executing those functions in the same order it was stored. Be carefully with this approach, if any execution fails, the relayer will get stuck as it would not be possible to guarantee delivery order.
This strategy will always execute the decorated function after current transaction commit. With this approach, we don't depend on a relayer (separate process / cronjob) to execute the decorated function and deliver the message. Failed items will only be retried through relayer. Although this solution has a better performance as only failed items is delivered by the relay command, we cannot guarantee delivery order.
We already provide a command to relay items from DB, EventRelayCommand. The way you should configure depends on the strategy you choose.
For example, on Publish on Commit Strategy you can configure a cronjob to run every a couple of minutes since only failed items are published by the command relay. If you are using Keep Order Strategy, you should run relay command in loop mode as all items will be published by the command, e.g call_command(events_relay.Command(), run_in_loop=True, loop_interval=0.1).
You can use Jaiminho's EventCleanerCommand in order to do that. It will query for all events that were sent before a given time interval (e.g. last 7 days) and will delete them from the outbox table.
The default time interval is 7 days. You can use the TIME_TO_DELETE setting to change it. It should be added to JAIMINHO_CONFIG and must be a valid timedelta.
You can run those commands in a cron job. Here are some config examples:
- name: relay-failed-outbox-events
schedule: "*/15 * * * *"
suspend: false
args:
- ddtrace-run
- python
- manage.py
- events_relay
resources:
requests:
cpu: 1
limits:
memory: 384Mi
- name: delete-old-outbox-events
schedule: "0 5 * * *"
suspend: false
args:
- ddtrace-run
- python
- manage.py
- event_cleaner
resources:
requests:
cpu: 1
limits:
memory: 384MiDifferent streams can have different requirements. You can save separate events per streams by using the @save_to_outbox_stream decorator:
@save_to_outbox_stream("my-stream")
def any_external_call(payload, **kwargs):
# do something
passyou can also overwrite publish strategy configure on settings:
@save_to_outbox_stream("my-stream", PublishStrategyType.KEEP_ORDER)
def any_external_call(payload, **kwargs):
# do something
passAnd then, run relay command with stream filter option
python manage.py relay_event True 0.1 my-streamIn the example above, True is the option for run_in_loop; 0.1 for loop_interval; and my_stream is the name of the stream.
Jaiminho triggers the following Django signals:
| Signal | Description |
|---|---|
| event_published | Triggered when an event is sent successfully |
| event_failed_to_publish | Triggered when an event is not sent, being added to the Outbox table queue |
You could use the Django signals triggered by Jaiminho to collect metrics. Consider the following code as example:
from django.dispatch import receiver
@receiver(event_published)
def on_event_sent(sender, event_payload, **kwargs):
metrics.count(f"event_sent_successfully {event_payload.get('type')}")
@receiver(event_failed_to_publish)
def on_event_send_error(sender, event_payload, **kwargs):
metrics.count(f"event_failed {event_payload.get('type')}")Create a virtualenv
virtualenv venv
pip install -r requirements-dev.txt
tox -e py39If you want to improve or suggest improvements, check our CONTRIBUTING.md file.
This project is licensed under MIT License.
If you have any security concern or report feel free to reach out to [email protected];