flux controller

[gberche-orange]

Describe the problem/challenge you have

kapp-controller and its ytt templating is great, and allowed me to overcome some limitations in kustomize flux workflows (see kubernetes-sigs/kustomize#4636)

However, kapp-controller and ytt does not integrate yet well with flux ecosystem, for flux consumer projects :

• the source (git repo/oci) are fetched independently :
  • from kapp fetch section
  • from flux source controller https://fluxcd.io/flux/components/source/
  • with different feature sets, e.g. kapp-controller does not yet support event-based pulls
• kapp-controller does not yet support notifications that flux could offer through the notification controller https://fluxcd.io/flux/components/notification/(see Integrate with notification providers (slack, teams ...)to reflect package install status/transitions #522)
• flux users also have to learn the kapp UX, and adapt their tooling see Plugin support for carvel kapp CR derailed/k9s#1830
• kapp controller does not yet have AFAIK builtin monitoring that flux could provide, see https://fluxcd.io/flux/guides/monitoring and [Docs] Collecting metrics from kapp-controller to observe cluster's app resources #789

Describe the solution you'd like

Carvel tools to also be integrated as a flux extension, see https://fluxcd.io/ecosystem/#flux-extensions

• step 1: a "all-in-one" carvel flux controller:
  • leveraging flux source events
  • with a consistent CRD ux and feature set to kustomize controller such as
    • spec.suspend to true
  • enabling all of carvel templating (e.g. ytt,cue...) and deploy (in particular kapp)
• step 2: fine grain controllers
  • a carvel templating flux controller
  • an option to leverage kapp for both
    • existing Kustomize controller
    • carvel templating flux controller

Anything else you would like to add:

This idea has been discussed in the carvel project history, and further exchanged during the community meeting on Jan 11th 2023, see https://hackmd.io/G8dN30WvQl-8Sirnp8AgRA?view#January-11-2023-Agenda

[Additional information that will assist in solving the issue.]

The https://fluxcd.io/flux/gitops-toolkit/source-watcher/ seems the entry point to spiking new flux controllers

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