feat(Warehouse): Subscribe to Git tags

[asolanki-mgni]

Proposed Feature

I would like to have the ability to have a Warehouse subscribe to git tags within a repo. When a new git tag is created I would like Kargo to create a freight so I can progress the freight to the different stages.

A promotionMechanism should also be created so I can update a values file with the newly created tag.

Motivation

We currently follow the apps of apps pattern in ArgoCD. We have helm--parent which sources multiple child apps. In the child apps, the devs can make the needed code changes (helm or image) and when changes are ready they will commit, merge and finally tag.

In the helm--parent repo, we manage the clusters that the child apps are deployed to with their specific version tags in different values files.

I would like to subscribe to a repo's git tags and when a new tag is created be able to have a promotionMechanism to update a values file with the new tag value.

Suggested Implementation

Warehouse:

apiVersion: kargo.akuity.io/v1alpha1
kind: Warehouse
metadata:
  name: git-tag-warehouse
spec:
  subscriptions:
  - git:
      repoURL: <git repo url>
      tag: <git tag regex>

Stage:

apiVersion: kargo.akuity.io/v1alpha1
kind: Stage
...
spec:
...
  promotionMechanisms:
    gitTagUpdates:
    - repoURL: <git repo url>
      writeBranch: <branch name>
      readBranch: <branch name>
      value: <tag value name>
      valuesFilePath: <values file path>

[krancour]

I would like to have the ability to have a Warehouse subscribe to git tags within a repo.

These features already exist.

You can set commitSelectionStrategy to Lexical, NewestTag, or SemVer. (The default is NewestFromBranch.)

It is a recently discovered oversight that for any fields constrained to specific enumerated values, the possible values are not surfacing in these generated docs:

https://doc.crds.dev/github.com/akuity/kargo/kargo.akuity.io/Warehouse/[email protected]#spec-subscriptions-git-commitSelectionStrategy

These is an issue already open to fix the same problem for imageSelectionStrategy.

#2880

I will expand that issue to include this.

A promotionMechanism should also be created so I can update a values file with the newly created tag.

fwiw, "promotion mechanisms" are legacy and were removed in 1.0.0.

1.0.0+ rely on promotion templates instead, which are enumerated, more finely-grained steps, so they allow more flexibility.

One of the steps added in 1.1 (to be released this week or next) is a generic YAML update. "Edge docs" here:

https://main.docs.kargo.io/references/promotion-steps#yaml-update