Better Developer experience with improved event discovery in Knative¶

Authors: David Simansky, Senior Software Engineer @ Red Hat, Matthias Weßendorf, Senior Principal Software Engineer @ Red Hat

Date: 2023-07-26

In this blog post you will learn about the new enhancements in Knative Eventing around event discovery.

Event discovery is an important part of event-driven applications, since it allows developers to better understand system dynamics and what events to consume. It does enable a more efficient and robust application design.

Knative Event Type API enhancements¶

With the latest 1.11 release of Knative Eventing there were a few improvements related to improved Event discovery:

EventType API bumped to v1beta2
Making use of references to point to any Resource like Channels or Sinks, not just brokers
Enhance build-in Sources to create eventypes for any binding, not just brokers.
Automatic EvenType creation for Brokers and Channels

EventType API changes and version bump¶

After a couple of years being on version v1beta1 the EventType API in Knative has changed and was bumped to v1beta2. The version bump did not come alone, it was combined with an overhaul for improved developer experience. It is now possible to point to any resource from an Event type object, instead of being only restricted to broker objects.

Referencing other resources¶

The new version is marking the broker field as deprecated and it will be removed in a future release, instead we now have the reference field which takes any KReference API type, being able to point to any sink, channel or the broker as well. Let's take a look at the new EventType object:

apiVersion: eventing.knative.dev/v1beta2
kind: EventType
metadata:
  name: dev.knative.source.github.push-sss34cnb
  namespace: default
spec:
  type: dev.knative.source.github.push
  source: https://github.com/knative/eventing
  reference:
    apiVersion: messaging.knative.dev/v1
    kind: InMemoryChannel
    name: testchannel

The status was also changed, since we do just require the reference to be existing, instead of being also ready itself.

Duck Sources¶

The above enhancement did allow an additional change for the build-in sources, or any source that is compliant to the Sources Duck type. For instance until previous releases EventType objects where only created automatically when the source was pointing to a broker, because of the above restriction. Now those are created for any referenced sink, on the source, like:

apiVersion: sources.knative.dev/v1
kind: PingSource
metadata:
  name: ping-source-broker2
spec:
  schedule: "*/1 * * * *"
  data: '{"message": "Hello world!"}'
  sink:
    ref:
      apiVersion: v1
      kind: Service
      name: log-receiver

This results in an auto-created event type, like:

k get eventtypes.eventing.knative.dev -A 
NAMESPACE   NAME                               TYPE                       SOURCE                                                        SCHEMA   REFERENCE NAME   REFERENCE KIND   DESCRIPTION   READY   REASON
default     93774a924a741245a94313745d78e69f   dev.knative.sources.ping   /apis/v1/namespaces/default/pingsources/ping-source-broker2            log-receiver     Service                        True

Auto Event Type creation¶

Furthermore to improve the experience with consumption and creation of EventTypes, there's a new experimental feature to automatically create EventTypes objects based on processed events on the broker ingress and in-memory channels. Instead of manually creating them as yaml manifests along the application code that talks to the Broker or Channel API. This behaviour can be enabled by feature flag eventtype-auto-creation in config-features ConfigMap. For futher details and examples please refer to the documentation.

Conclusion¶

This blog post introduced new features and improvements to EventType discoroverability. The main motivation is to harden the position of developer's insight into the event-driven applications to ease up the discovery and speed up development.

We look forward from the community to further enhance EventType API and discoverability. Please reach out on the CNCF Slack's #knative-eventing or GitHub issues.