Use the Open edX Event Bus to Broadcast and Consume Events

Use the Open edX Event Bus to Broadcast and Consume Events#

Note

Be sure to check out how to make your Open edX Event event bus compatible in the Add Event Bus Support to an Open edX Event guide.

After creating a new Open edX Event, you might need to send it across services instead of just within the same process. For this kind of use-cases, you might want to use the Open edX Event Bus. Here Open edX Event Bus, you can find useful information to start getting familiar with the Open edX Event Bus.

The Open edX Event Bus is a key component of the Open edX architecture, enabling services to communicate without direct dependencies on each other. This guide provides an overview of how to use the event bus to broadcast Open edX Events to multiple services, allowing them to react to changes or actions in the system.

Assumptions#

  • You have a development environment set up using Tutor.

  • You have a basic understanding of Python and Django.

  • You have basic understanding of the Open edX Event Bus. If not, you can review the Open edX Event Bus docs.

  • You understand the concept of filters or have reviewed the relevant Concepts docs.

  • You are familiar with the terminology used in the project, such as the terms Event Type or Topic. If not, you can review the Open edX Events Glossary docs.

Steps#

To start producing and consuming events using the Open edX Event Bus, follow these steps:

Step 1: Install the Open edX Event Bus Plugin#

First, you need to install the Open edX Event Bus plugin in both the producing and consuming services. The plugin is a Django app that provides the necessary tools and configurations to produce and consume events. You could install the Redis plugin by running:

pip install edx-event-bus-redis

Note

There are currently two community-supported concrete implementations of the Open edX Events Bus, Redis (event-bus-redis) and Kafka (event-bus-kafka). Redis is the default plugin for the Open edX Event Bus, but you can also use Kafka depending on your requirements. If none of these implementations meet your needs, you can implement your own plugin by following the Add a New Concrete Implementation of the Event Bus documentation.

Step 2: Configure the Event Bus#

In Event Bus Configuration, you can find the available configurations for the event bus that are used to set up the event bus in the Open edX platform.

In both the producing and consuming services, you need to configure the event bus. This includes setting up the event types, topics, and other configurations for the Event Bus to work with. In this step, you should configure the producer and consumer classes for the event bus implementation you are using:

  • In the producing service, configure the producer class by setting the EVENT_BUS_PRODUCER setting. E.g., edx_event_bus_redis.create_producer.

  • In the consuming service, configure the consumer class by setting the EVENT_BUS_CONSUMER setting. E.g., edx_event_bus_redis.RedisEventConsumer.

By configuring these settings, you are telling Open edX Events which concrete implementation to use for producing and consuming events.

Step 3: Produce the Event#

In the producing/host application, include openedx_events in INSTALLED_APPS settings if necessary and add EVENT_BUS_PRODUCER_CONFIG setting. This setting is a dictionary of event types to dictionaries for Topic related configuration. Each Topic configuration dictionary uses the topic as a key and contains:

  • A flag called enabled denoting whether the event will be published.

  • The event_key_field which is a period-delimited string path to event data field to use as event key.

Note

The topic names should not include environment prefix as it will be dynamically added based on EVENT_BUS_TOPIC_PREFIX setting.

Here’s an example of the producer configuration which will publish events for XBlock published and deleted events to the specified Topic:

EVENT_BUS_PRODUCER_CONFIG = {
     'org.openedx.content_authoring.xblock.published.v1': {
         'content-authoring-xblock-lifecycle': {'event_key_field': 'xblock_info.usage_key', 'enabled': True},
         'content-authoring-xblock-published': {'event_key_field': 'xblock_info.usage_key', 'enabled': True}
     },
     'org.openedx.content_authoring.xblock.deleted.v1': {
         'content-authoring-xblock-lifecycle': {'event_key_field': 'xblock_info.usage_key', 'enabled': True},
     },
}

Where:

  • org.openedx.content_authoring.xblock.published.v1 and org.openedx.content_authoring.xblock.deleted.v1 are the event types.

  • content-authoring-xblock-lifecycle and content-authoring-xblock-published are the topics to which the events will be published. The topic names can take any value, but it is recommended to use a meaningful name.

  • event_key_field is the path to the field in the event data that will be used as the event key.

The EVENT_BUS_PRODUCER_CONFIG is read by openedx_events and a handler (general_signal_handler) is attached which does the leg work of reading the configuration again and pushing to appropriate handlers.

Step 4: Consume the Event#

In the consuming service, include openedx_events in INSTALLED_APPS settings if necessary and add EVENT_BUS_CONSUMER_CONFIG setting. Then, you should implement a receiver for the event type you are interested in. In this example, we are interested in the XBlock deleted event:

@receiver(XBLOCK_DELETED)
def update_some_data(sender, **kwargs):
... do things with the data in kwargs ...
... log the event for debugging purposes ...

Step 5: Run the Consumer#

To consume events, Open edX Events provides a management command called consume_events which can be called from the command line, how to run this command will depend on your deployment strategy. This command will start a process that listens to the message broker for new messages, processes them and emits the event. Here is an example using of a consumer using Tutor hosted in Kubernetes.

You can find more a concrete example of how to produce and consume events in the event-bus-redis documentation.

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