docs: [FC-0074] add docs about creating and consuming events

docs/concepts/event-bus.rst

@@ -119,7 +119,7 @@ How is the Open edX Event Bus Used?
 
 The event bus is used to broadcast Open edX Events to multiple services, allowing them to react to changes or actions in the system.
 
-We encourage you to review the :doc:`../reference/real-life-use-cases` page for examples of how the event bus is used in the Open edX ecosystem by the community. Also, see the :doc:`../how-tos/using-the-event-bus` guide to get start sending events to the event bus.
+We encourage you to review the :doc:`../reference/real-life-use-cases` page for examples of how the event bus is used in the Open edX ecosystem by the community. Also, see the :doc:`../how-tos/use-the-event-bus-to-broadcast-and-consume-events` guide to get start sending events to the event bus.
 
 .. _general_signal_handler: https://github.com/openedx/openedx-events/blob/main/openedx_events/apps.py#L16-L44
 .. _EventProducer: https://github.com/openedx/openedx-events/blob/main/openedx_events/event_bus/__init__.py#L71-L91

docs/concepts/openedx-events.rst

@@ -75,7 +75,7 @@ How are Open edX Events used?
 
 As mentioned previously, developers can listen to Open edX Events by registering signal receivers from their Open edX Django plugins that respond to the emitted events or by using the :doc:`../concepts/event-bus` to send events to external services.
 
-For more information on using Open edX Events, refer to the :doc:`../how-tos/using-events` how-to guide. We also encourage you to explore the :doc:`../reference/real-life-use-cases` section for real-life examples of how Open edX Events are used by the community.
+For more information on using Open edX Events, refer to the :doc:`../how-tos/create-a-new-event` how-to guide. We also encourage you to explore the :doc:`../reference/real-life-use-cases` section for real-life examples of how Open edX Events are used by the community.
 
 .. _Django Signals Documentation: https://docs.djangoproject.com/en/4.2/topics/signals/
 .. _triggering the COURSE_ENROLLMENT_CREATED event: https://github.com/openedx/edx-platform/blob/master/common/djangoapps/student/models/course_enrollment.py#L777-L795

docs/decisions/0016-event-design-practices.rst

@@ -26,7 +26,7 @@ Event Purpose and Content
 ~~~~~~~~~~~~~~~~~~~~~~~~~
 
 - An event should describe as accurately as possible what happened (what) and why it happened (why). It must contain enough information for consumers to understand the message. For instance, if an event is about a user enrollment, it should contain the user's data, the course data, and the enrollment status and the event should be named accordingly.
-- Avoid immediately contacting the source service to retrieve additional information. Instead, consider adding the necessary information to the event payload by managing the granularity of the event. If the event requires additional information, consider adding a field to the event that contains the necessary information. This will reduce the number of dependencies between services and make the event more self-contained.
+- Avoid immediately contacting the source service to retrieve additional information from the consumer-side. Instead, consider adding the necessary information to the event payload by managing the granularity of the event. If the event requires additional information, consider adding a field to the event that contains the necessary information. This will reduce the number of dependencies between services and make the event more self-contained.
 - Keep the event size small. Avoid adding unnecessary information to the event. If the information is not necessary for consumers to react to the event, consider removing it.
 - Avoid adding flow-control information or business logic to events. Events should be solely a representation of what took place. If a field is necessary to control the behavior of the consumer, consider moving it to the consumer side. If adding additional data to the event is absolutely necessary document the reasoning behind it and carefully study the use case and implications.
 
@@ -53,6 +53,11 @@ Some of these practices might not be applicable to all events, but they are a go
 
 In addition to these practices, review the Architectural Decision Records (ADRs) related to events to understand the naming, versioning, payload, and other practices that are specific to Open edX events.
 
+Consequences
+------------
+
+Following these practices will help ensure that the events are consistent, maintainable, and reusable. It will also help consumers understand the message and react to the event accordingly. However, it might require additional effort to design the event and ensure that it contains the necessary information for consumers to react to the event, although this effort will pay off in the long run. Having these standards in place will also make the decision process easier when designing new events.
+
 .. _Event-Driven Microservices: https://www.oreilly.com/library/view/building-event-driven-microservices/9781492057888/
 .. _Event-Driven article: https://martinfowler.com/articles/201701-event-driven.html
 .. _Thin Events - The lean muscle of event-driven architecture: https://www.thoughtworks.com/insights/blog/architecture/thin-events-the-lean-muscle-of-event-driven-architecture

docs/how-tos/add-new-event-bus-concrete-implementation.rst

@@ -1,5 +1,5 @@
-How to add a new concrete implementation of the event bus
-=========================================================
+Add a New Concrete Implementation of the Event Bus
+==================================================
 
 Context
 -------

docs/how-tos/consume-an-event.rst

@@ -0,0 +1,132 @@
+Consume an Open edX Event
+=========================
+
+You have two ways of consuming an Open edX event, within the same service or in a different service. In this guide, we will show you how to consume an event within the same service. For consuming events across services, see :doc:`../how-tos/use-the-event-bus-to-broadcast-and-consume-events`.
+
+.. note:: We encourage you to also consider the practices outlined in the :doc:`../decisions/0016-event-design-practices` ADR for event consumption.
+
+Throughout this guide, we will implement the use case to send the enrollment data to a webhook when a user enrolls in a course to better illustrate the steps involved in creating a consumer for an event.
+
+Assumptions
+-----------
+
+- You have a development environment set up using `Tutor`_.
+- You have a basic understanding of Python and Django.
+- You have a basic understanding of Django signals. If not, you can review the `Django Signals Documentation`_.
+- You are familiar with the terminology used in the project, such as the terms :term:`Event Type` or :term:`Event Receiver`. If not, you can review the :doc:`../reference/glossary` documentation.
+
+Steps
+-----
+
+To consume an event within the same service, follow these steps:
+
+Step 1: Understand your Use Case and Identify the Event to Consume
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Before you start consuming an event, you should understand the use case and the event you want to consume, for this review the `list of events`_ available in the Open edX platform. In this case, we want to send the enrollment data to a webhook when a user enrolls in a course. You should review the event definition and payload to understand the data that is being passed to the event receiver and how you can use it to implement the custom logic.
+
+In our example, we want to send the enrollment data to a webhook when a user enrolls in a course. We will consume the ``COURSE_ENROLLMENT_CREATED`` event, which is triggered every time a user enrolls in a course. You can review the event definition and payload to understand the data that is being passed to the event receiver and how you can use it to implement the request to the webhook.
+
+Step 2: Install Open edX Events
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+First, add the ``openedx-events`` plugin into your dependencies so the library's environment recognizes the event you want to consume. You can install ``openedx-events`` by running:
+
+.. code-block:: bash
+
+   pip install openedx-events
+
+This will mainly make the events available for your CI/CD pipeline and local development environment. If you are using the Open edX platform, the library should be already be installed in the environment so no need to install it.
+
+Step 3: Create a Event Receiver and Connect it to the Event
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+An :term:`Event Receiver` is simply a function that listens for a specific event and executes custom logic in response to the event being triggered. You can create an event receiver by using the Django signal receivers decorator. Here's an example of an event receiver that listens for the ``COURSE_ENROLLMENT_CREATED`` event and creates a notification preference for the user:
+
+.. code-block:: python
+
+    from openedx_events import COURSE_ENROLLMENT_CREATED
+    from django.dispatch import receiver
+
+    @receiver(COURSE_ENROLLMENT_CREATED)
+    def send_enrollment_data_to_webhook(signal, sender, enrollment, metadata, **kwargs):
+        # Custom logic to send enrollment data to a webhook
+        pass
+
+- The Django dispatcher will call the ``send_enrollment_data_to_webhook`` function when the ``COURSE_ENROLLMENT_CREATED`` event is triggered by using the ``receiver`` decorator. In this case, that would be every time a user enrolls in a course.
+- Consider using asynchronous tasks to handle the event processing to avoid blocking the main thread and improve performance. Also, make sure to handle exceptions and errors gracefully to avoid silent failures and improve debugging. You should also consider not creating a tight coupling between receivers and other services, if doing so is necessary consider using the event bus to broadcast the event.
+- When implementing the receiver, inspect the event payload to understand the data that is being passed to the event receiver by reviewing the ``data.py`` file of the event you are consuming. For example, the ``COURSE_ENROLLMENT_CREATED`` event has the following payload:
+
+.. code-block:: python
+
+    # Location openedx_events/learning/data.py
+    COURSE_ENROLLMENT_CREATED = OpenEdxPublicSignal(
+        event_type="org.openedx.learning.course.enrollment.created.v1",
+        data={
+            "enrollment": CourseEnrollmentData,
+        }
+    )
+
+- This event has a single field called ``enrollment`` which is an instance of the ``CourseEnrollmentData`` class. You can review the ``CourseEnrollmentData`` class to understand the data that is available to you and how you can use it to implement the custom logic.
+- The ``metadata`` parameter contains the Open edX-specific metadata for the event, such as the event version and timestamp when the event was sent. You can use this metadata to understand more about the event and its context.
+
+These event receivers are usually implemented independently of the service in an `Open edX Django plugins`_ and are registered in the ``handlers.py`` (according to `OEP-49`_) file of the plugin. You can review the ``handlers.py`` file of the `openedx-events-2-zapier`_ plugin to understand how the event receivers are implemented and connected to the events.
+
+.. TODO: change receivers.py in openedx-events-2-zapier to handlers.py
+
+Consider the following when implementing the event receiver:
+
+- Limit each receiver to a single responsibility to make the code easier to maintain and test.
+- Keep the receiver logic simple and focused on the specific task it needs to perform.
+- Consider the performance implications of the receiver and avoid adding unnecessary complexity or overhead, considering that receivers will be executed each time the event is triggered. Consider using asynchronous tasks to handle the event processing to avoid blocking the main thread and improve performance.
+- Implement error handling and logging in the pipeline step to handle exceptions and provide useful information for debugging, considering both development and production environments.
+
+Step 4: Test the Event Receiver
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Given the design of Open edX Events, you can include the events definitions in your test suite to ensure that the event receiver is working as expected. You can use the ``send_event`` method to trigger the event and test the event receiver. Here's an example of how you can test the event receiver:
+
+.. code-block:: python
+
+    from openedx_events import send_event, COURSE_ENROLLMENT_CREATED
+
+    def test_send_enrollment_data_to_webhook(self):
+        # Trigger the event
+        enrollment_data = CourseEnrollmentData(
+            user=UserData(
+                pii=UserPersonalData(
+                    username=self.user.username,
+                    email=self.user.email,
+                    name=self.user.profile.name,
+                ),
+                id=self.user.id,
+                is_active=self.user.is_active,
+            ),
+            course=CourseData(
+                course_key=self.course.id,
+                display_name=self.course.display_name,
+            ),
+            mode=self.course_enrollment.mode,
+            is_active=self.course_enrollment.is_active,
+            creation_date=self.course_enrollment.created,
+        )
+
+        COURSE_ENROLLMENT_CREATED.send_event(
+            enrollment=enrollment_data
+        )
+
+        # Assert that the request was sent to the webhook with the correct data
+
+- In the test suite, you can use the ``send_event`` method to trigger the event and pass the necessary data to the event receiver. In this case, we are passing the user, course and enrollment data to the event receiver as the triggering logic would do.
+- After triggering the event, you can assert that the event receiver executed the custom logic as expected. In this case, we are checking that the request was sent to the webhook with the correct data.
+
+You can review this example to understand how you can test the event receiver and ensure that the custom logic is executed when the event is triggered in the `openedx-events-2-zapier`_ plugin.
+
+This way you can ensure that the event receiver is working as expected and that the custom logic is executed when the event is triggered. If the event definition or payload changes in any way, you can catch the error in the test suite instead of in production.
+
+.. _Tutor: https://docs.tutor.edly.io/
+.. _Django Signals Documentation: https://docs.djangoproject.com/en/4.2/topics/signals/
+.. _openedx-events-2-zapier: https://github.com/eduNEXT/openedx-events-2-zapier
+.. _Open edX Django plugins: https://docs.openedx.org/en/latest/developers/concepts/platform_overview.html#new-plugin
+.. _OEP-49: https://docs.openedx.org/projects/openedx-proposals/en/latest/best-practices/oep-0049-django-app-patterns.html#signals
+.. _list of events: https://docs.openedx.org/projects/openedx-events/en/latest/reference/events.html