[RFC] Flux-CDEvent Provider

rfcs/NNNN-cdevents-provider/README.md

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+# Flux CDEvents Provider
+
+<!--
+The title must be short and descriptive.
+-->
+
+**Status:** provisional
+
+<!--
+Status represents the current state of the RFC.
+Must be one of `provisional`, `implementable`, `implemented`, `deferred`, `rejected`, `withdrawn`, or `replaced`.
+-->
+
+**Creation date:** 2024-01-19
+
+**Last update:** 2024-06-05
+
+## Summary
+
+This RFC proposes to add a `Provider` type to the Flux notification-controller API for sending
+[CDEvents](https://github.com/cdevents).
+
+When `Provider` objects configured to send CDEvents are alerted by a Flux event, they will utilise an already defined
+mapping of Flux and CDEvents events to send an appropriate CDEvent payload to a defined URL.
+<!--
+One paragraph explanation of the proposed feature or enhancement.
+-->
+
+## Motivation
+
+CDEvents enables interoperability between supported  tools in a workflow, and flux is a very popular continuous delivery
+tool, as such we have received many questions about implementing CDEvents into the tool. The receiver part of this
+integration is already implemented in flux 2.3.0
+<!--
+This section is for explicitly listing the motivation, goals, and non-goals of
+this RFC. Describe why the change is important and the benefits to users.
+-->
+
+### Goals
+
+Integrate [CDEvents](https://github.com/cdevents) into Flux with a CDEvents Provider that supports sending CDEvent
+events.
+
+<!--
+List the specific goals of this RFC. What is it trying to achieve? How will we
+know that this has succeeded?
+-->
+
+### Non-Goals
+
+Implementing CDEvents into every Flux controller that is not the notification controller. 
+
+<!--
+What is out of scope for this RFC? Listing non-goals helps to focus discussion
+and make progress.
+-->
+
+## Proposal
+
+Add CDEvents to the list of available `Providers` in Flux Notification controller. The relevant CDEvent sent by the
+`Provider` will be determined by a pre-defined mapping of Flux events and relevant CDEvents. These CDEvent payloads
+should have meaningful data from the source event. There will be an initial focus on HelmRelease and related events as
+the format within Flux for those events is much more consistent.
+<!--
+This is where we get down to the specifics of what the proposal actually is.
+This should have enough detail that reviewers can understand exactly what
+you're proposing, but should not include things like API designs or
+implementation.
+
+If the RFC goal is to document best practices,
+then this section can be replaced with the actual documentation.
+-->
+
+### User Stories
+
+Users of multiple CI/CD tools such as Tekton and Flux could use CDEvents as a way to enable interoperability.
+
+For example, a user may want a Tekton `pipeline` to run once a HelmRelease flux resource has succeeded in a Helm
+install. On successful helm install, Flux will emit an event with reason `InstallSucceeded` which will be mapped to an
+`Environment.Modified` CDEvent. The CDEvent `Provider` will then send a payload with that CDEvent, which will also
+contain data from the Flux event, to a CloudEvents broker that Tekton is subscribed to, and trigger a Pipeline Run
+within Tekton. 
+
+![User Stories Tekton](user-stories-provider.drawio.png)
+
+
+<!--
+Optional if existing discussions and/or issues are linked in the motivation section.
+-->
+
+### Alternatives
+
+There are currently no viable alternatives for the CDEvent Provider.
+<!--
+List plausible alternatives to the proposal and explain why the proposal is superior.
+
+This is a good place to incorporate suggestions made during discussion of the RFC.
+-->
+
+## Design Details
+
+Adding a Flux `Provider` for CDEvents that will send a CDEvent payload upon receiving a flux event from an alert. 
+
+Once an alert is triggered for this provider, it will send a CDEvent that corresponds to the Flux event that caused the
+alert. This CDEvent will be created using the [CDEvents Go SDK](https://github.com/cdevents/sdk-go). The implementation
+will include a defined mapping of which Flux events trigger a corresponding CDEvent.
+
+The CDEvents broker is not a part of this design and is left to the users to set up however they wish.
+
+Example Provider YAML:
+
+```yaml
+apiVersion: notification.toolkit.fluxcd.io/v1beta2
+kind: Provider
+metadata:
+  name: cdevents-provider
+  namespace: flux-system
+spec:
+  type: cdevents
+  secretRef:
+    name: generic-token
+  address: http://10.100.0.17:5000
+```
+
+Example Default Mappings (Please note these are not final and will be open to discussion):
+
+| Helm Event                | CDEvent                         |
+| ------------------------- | ------------------------------- |
+| InstallSucceeded          | Service.Deployed            |
+| InstallFailed             | Incident.Detected               |
+| UpgradeSucceeded          | Service.Upgraded               |
+| UpgradeFailed              | Incident.Detected |
+| TestSucceeded              | TestCaseRun.finished (outcome pass)           | 
+| TestFailed                 | TestCaseRun.finished (outcome fail)              | 
+| RollbackSucceeded          | Service.RolledBack          |
+| RollbackFailed             | Incident.Detected          |
+| UninstallSucceeded         | Service.Removed          |
+| UninstallFailed            | Incident.Detected               |
+
+<!--
+This section should contain enough information that the specifics of your
+change are understandable. This may include API specs and code snippets.
+
+The design details should address at least the following questions:
+- How can this feature be enabled / disabled?
+- Does enabling the feature change any default behavior?
+- Can the feature be disabled once it has been enabled?
+- How can an operator determine if the feature is in use?
+- Are there any drawbacks when enabling this feature?
+-->
+
+## Implementation History
+
+<!--
+Major milestones in the lifecycle of the RFC such as:
+- The first Flux release where an initial version of the RFC was available.
+- The version of Flux where the RFC graduated to general availability.
+- The version of Flux where the RFC was retired or superseded.
+-->