Support Step life-cycle hooks in a "listener" Sidecar

[skaegi]

A frequent request we are hearing from users, is the ability to watch and react as the Steps of a Task proceed without having to necessarily hard-code that logic into Steps. For example firing a Slack message when a particular Step completes or updating a PR as various tests complete.

I wonder if we might re-use a mechanism similar to https://kubernetes.io/docs/concepts/containers/container-lifecycle-hooks/ to notify a "listener" sidecar. Once notified the sidecar shares the /workspace so might run further interesting logic. This might be a way to peel another useful piece of the PipelineResource capability away.

[ghost]

Relates to #1460 I think.

[dibyom]

/kind feature

[dibyom]

Somewhat related to #1740

Perhaps we can emit CloudEvents that the entrypoint can send to some user defined sink?

[bobcatfish]

This does sound to me like what "notifications" are about, what do you think @skaegi ?

To summarize, open issues that might solve this:

• Optionally emit events during execution #2082 - Emit events during execution
• Actions and Notifications for Tekton #1740 - Notifications and actions

[skaegi]

Yes. I guess what I was trying to figure out is if there was some pre-existing approach in Kubernetes that we could use to "act" on the events.

[MLBMatt]

So for a real-world example, we (MLB) run a sidecar container that leverages kubernetes-client to listen in on the pod (pipeline) in question and reports back statuses into Github. Definitely has it's quirks but seems to be working well thus far.

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[wlynch]

/reopen
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@wlynch: Reopened this issue.

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