Proposal: Cloud Events Controller and CDEvents

Feature request

Introduce a controller dedicated to sending CloudEvents in the format specified by the CDF SIG Events / CDEvents, which can be later extended to support multiple formats of CloudEvents and events specific options and features.

Tekton defines low level abstractions like Tasks and Pipelines. The SIG Events protocol defines higher level abstractions too, like “Change”, “Build”, “Deployment” and more.
When Tekton is used through an opinionated CI/CD system on top, Tekton would send the events related to tasks and pipelines only. When Tekton is used standalone, we would like to provide users a mechanism to identify their Tekton Tasks and Pipelines as implementations of higher level abstractions, and have Tekton send the corresponding events too. This would be most likely implemented through some form of annotation on Tekton resources.

We would like to start with a project in the tektoncd/experimental repo, with the end goal to either incorporated into tektoncd/pipeline or alternatively become a new project in the tektoncd org. Initial owners of the project will be Vibhav Bobade and Andrea Frittoli.

As described in the community repo, the first step is to present the idea in a WG.
This was done in the WG on Wed May 26th. The next step is to create an issue in the community repo.

Use case

The CDF SIG Events mission is to define a common event based protocol for CI/CD systems to interoperate. An initial draft of the protocol specification is available on the SIG repo. The protocol is based on CloudEvents.

Tekton can already generate CloudEvents for several events, but the format of such events is Tekton specific, and cannot be customized.

Interoperability is key to the success of Tekton, and supporting this new format of CloudEvents would help DevOps engineers and architects integrating Tekton with other CI/CD systems as well as collecting metrics from heterogeneous CI/CD workflows.

Additional Information

It was already proposed to move Tekton support for CloudEvents to a dedicated binary / controller. This work could align with that proposal and implement a controller that could send both the existing format as well as new formats of CloudEvents.

Start by reviewing the CDF SIG Events vocabulary draft, the existing Tekton CloudEvents documentation, and proposal #2944 about moving CloudEvents support to a dedicated controller. Clarify the WG and project-scope decisions before defining what completion means: a controller in tektoncd/experimental that can emit CDEvents and identify higher-level resource types through annotations.