Pipeline Implementation

[vaikas]

Fixes #1067

Proposed Changes

• Add messaging.knative.dev/pipelines for being able to define simple sequences

Release Note

Adds a pipeline (sequence of functions to execute in order) with an optional Reply to send results to.

[knative-prow-robot]

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[lionelvillard]

@vaikas-google If you want I can take an initial stab at the reconciler. LMK.

[vaikas]

I wired a pipeline like this (using IMC (After my fix that got merged earlier today)), and the following pipeline worked, verified the data flew through the pipeline:
apiVersion: messaging.knative.dev/v1alpha1
kind: Pipeline
metadata:
name: vaikas-pipeline
namespace: foobar
spec:
channelTemplate:
apiVersion: messaging.knative.dev/v1alpha1
kind: InMemoryChannel
steps:

• ref:
  apiVersion: serving.knative.dev/v1alpha1
  kind: Service
  name: first
• ref:
  apiVersion: serving.knative.dev/v1alpha1
  kind: Service
  name: second
• ref:
  apiVersion: serving.knative.dev/v1alpha1
  kind: Service
  name: third

[vaikas]

If it looks good, I'll work on the validation / docs after this, but given the shift in time, unless there's something major that can't be fixed in a followup, I'd like to get this merged so that I don't have to keep rebasing :)
@lionelvillard @Harwayne

[n3wscott]

/lgtm

[Harwayne]

/hold

I want to review the changes.

[Harwayne]

This isn't quite accurate, a Channelable may be addressable but not ready.

For now, I'm OK with a TODO.

[vaikas]

Yes, I had a TODO there (and dropped it somewhere along the way), and I think we need to change Channelable a little bit, because it doesn't include anything useful besides this.

[Harwayne]

/hold cancel
/lgtm

[knative-metrics-robot]

The following is the coverage report on pkg/.
Say /test pull-knative-eventing-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/apis/messaging/v1alpha1/pipeline_defaults.go	Do not exist	0.0%
pkg/apis/messaging/v1alpha1/pipeline_lifecycle.go	Do not exist	98.1%
pkg/apis/messaging/v1alpha1/pipeline_types.go	Do not exist	0.0%
pkg/apis/messaging/v1alpha1/pipeline_validation.go	Do not exist	94.4%
pkg/reconciler/pipeline/pipeline.go	Do not exist	71.7%