django-jaiminho 1.1.0

A broker agnostic implementation of outbox and other message resilience patterns for Django apps

jaiminho

A broker agnostic implementation of outbox and other message resilience patterns for django apps.

Installation

python -m pip install jaiminho

Add jaiminho in the INSTALLED_APPS section of your Django app

Usage

We provide a @save_to_outbox decorator that you can use in the functions responsible to communicate with external systems (brokers, external APIs, etc). Behind the scenes, jaiminho can store those functions calls in a local table in the same database within the current transaction. It can relay those functions calls after a success commit and/or a separate relay command, fixing the dual writes issue.

from jaiminho.send import save_to_outbox

@save_to_outbox
def any_external_call(**kwargs):
    # do something
    return

Configure jaiminho options in Django settings.py:

# JAIMINHO

JAIMINHO_CONFIG = {
    "PERSIST_ALL_EVENTS": False,
    "DELETE_AFTER_SEND": True,
    "DEFAULT_ENCODER": DjangoJSONEncoder,
    "PUBLISH_STRATEGY: "publish-on-commit"
    }

Configuration options

• PUBLISH_STRATEGY - Which strategy use to publish events (publish-on-commit, keep-order)
• PERSIST_ALL_EVENTS - Saves all events and not only the ones that fail, default is False. 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 send
• DEFAULT_ENCODER - Default Encoder for the payload (overwritable in the function call)

Strategies

Keep Order

This strategy is similar to transactional outbox described by Chris Richardson. The decorated function intercepts the function call and saves it on 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. Otherwise, would not possible to guarantee delivery order.

Publish on commit

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 executed through relayer. Despite we can decrease the delay to execute the decorated function with this approach, we cannot guarantee delivery order.

Relay Command

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).

Signals

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 failed to be send and it's enqueue to the Outbox table

How to collect metrics from Jaiminho?

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')}")

How to clean older events

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.

Relay per stream and Overwrite publish strategy

Different streams can have different requirements. You can save separate events per streams by using @save_to_outbox_stream decorator:

@save_to_outbox_stream("my-stream")
def any_external_call(payload, **kwargs):
    # do something
    pass

you 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
    pass

And then, run relay command with stream filter option

python manage.py relay_event True 0.1 my-stream

Where True is option for run_in_loop, 0.1 is loop_interval and my_stream is the stream name.

Development

Create a virtualenv

virtualenv venv
pip install -r requirements-dev.txt
tox -e py39

Collaboration

If you want to improve or suggest improvements, check our CONTRIBUTE.md file.

License

This project is licensed under MIT License.

Security

If you have any security concern or report feel free to reach out to [e-mail];