Embed TriggerBinding in EventListener triggers

[ncskier]

Expected Behavior

I expect to be able to send static parameters to my TriggerTemplate without creating an extra TriggerBinding resource to define these parameters in.

Actual Behavior

In v0.1.0, we had a params field in the EventListener:

apiVersion: tekton.dev/v1alpha1
kind: EventListener
metadata:
  name: listener-interceptor
spec:
  serviceAccountName: tekton-triggers-example-sa
  triggers:
    - name: foo-trig
      binding:
        name: pipeline-binding
      template:
        name: pipeline-template
      params:
      - name: message
        value: Hello from the Triggers EventListener!

This field made it very easy for me to send static parameters to my TriggerTemplate. However, we removed it with the v0.2.0 release, because parameters were replaced with multiple TriggerBindings. So, now I must create a separate TriggerBinding resource with static parameters to use in my EventListener.
I expect to be able to define my static parameters in the EventListener. Having to create a separate TriggerBinding resource with my parameters is annoying.

I think that a nice solution to this problem is to implement the option to embed TriggerBindings in the EventListener. The implementation could be similar to how Tekton Pipelines handles embedding PipelineResources. They have a resourceRef or resourceSpec for each PipelineResource used in a TaskRun or PipelineRun (more info here). Similarly, we could have a bindingRef or bindingSpec for each TriggerBinding used in an EventListener.

[dibyom]

/kind feature

[khrm]

/assign

[khrm]

We might have to go with supporting embedding in TriggerCRD if we implement that for solving EL pod proliferation issue.

[ncskier]

Yep, I think that's true. However, I don't think that it affects this issue right now. The inherent structure of how TriggerBindings are used will remain the same.

Plus, I assume that if we decide to make a separate TriggerCRD, then there will be a discussion about whether or not to allow users to embed the TriggerCRD in an EventListener.

[ncskier]

@khrm are you still working on this issue? Since there isn't a PR yet, we'll probably want to push this issue back into the v0.4.0 release.