Keda: Provide CloudEvent to extend KEDA

[tomkerkhove]

Provide CloudEvent that are emitted by the runtime so that customers can extend KEDA.

Events that come to mind are:

• New Trigger Authentication Created
• Deployment Scaled to Zero
• New Scaled Object Created
• Information on scaling action
• Information about new scaled object referencing existing trigger authentication

Only concern I have is that folks could go through the Kubernetes eventing approach to get the information, but if we would emit it ourselves we could make it more user friendly rather than having to figure this out via the Kube way

[tomkerkhove]

Thoughts @jeffhollan?

[zroubalik]

We should definitely implement the Kuberenetes eventing approach (created https://github.com/kedacore/keda/issues/530). This could be lower priority item.

[tomkerkhove]

Thanks for that! Since Kubernetes doens't support CloudEvents (yet), I would leverage this as a seperate component as well to make it easier to integrate with other products/tools that are not Kubernetes event specific.

See https://github.com/kubernetes/kubernetes/issues/85544 for CloudEvents support in Kubernetes.

[tomkerkhove]

The reason for that is that, for most scenarios you'd want to react on these events, and these workloads are not always in Kubernetes. If we only support Kubernetes events how it is today, events are stuck inside the cluster so they are, in my opinion, often pointless.

If we have CloudEvents, we can just forward them to things like Azure Event Grid and take it from there with FaaS/SaaS/PaaS services like Azure Functions.