Holos writes fully rendered manifests to the local filesystem, a gitops repository. Kargo watches a container registry for new images, then uses the rendered manifests Holos produced as the input to the promotion process.
The specific integration point I explored last week was configuring Holos to write a Kustomize kustomization.yaml file along side each of the components that have promotable artifacts. This is essentially just a stub for Kargo to come along and edit with a promotion step.
For example the output of the Holos rendering process for our demo "Bank of Holos" front end is this directory:
https://github.com/holos-run/bank-of-holos/tree/v0.6.2/deplo...
Normally, ArgoCD would deploy this straight from Git, but we changed the Application resource we configure to instead look where Kargo suggests, which is a different branch. Aside, I'm not sure I like the multiple branches approach but I'm following Kargo's docs initially then will look at doing it again in the same branch but using different folders.
https://github.com/holos-run/bank-of-holos/blob/v0.6.2/deplo...
Note the targetRevision: stage/dev Kargo is responsible for this branch.
The Kargo promotion stages are configured by this manifest Holos renders:
https://github.com/holos-run/bank-of-holos/blob/v0.6.2/deplo...
Holos writes this file out from the CUE configuration when it renders the platform. The corresponding CUE configuration responsible for producing that rendered manifest is at:
https://github.com/holos-run/bank-of-holos/blob/v0.6.2/proje...
This is all a very detailed way of saying: Holos renders the manifests, you commit them to git, Kargo uses Kustomize edit to patch in the promoted container image and renders the manifests _again_ somewhere else (branch or folder). ArgoCD applies the manifests Kargo writes.
I'll write it up properly soon, but the initial notes from my spike last week are at https://github.com/holos-run/bank-of-holos/blob/main/docs/ka...
I recorded a quick video of it at https://www.youtube.com/watch?v=m0bpQugSbzA which is more a demo of Kargo than Holos really.
What we were concerned about was we'd need to wait for Kargo to support arbitrary commands as promotion steps, something they're not targeting on having until v1.3 next year. Luckily, we work very well with their existing promotion steps because we take care to stop once we write the rendered manifests, leaving it up you to use additional tools like kubectl apply, Kargo, Flux, ArgoCD, etc...
