Stage sourced by multiple warehouses always result in error when promoting first time

[kejne]

Checklist

• [x] I've searched the issue queue to verify this is not a duplicate bug report.
• [x] I've included steps to reproduce the bug.
• [x] I've pasted the output of kargo version.
• [ ] I've pasted logs, if applicable.

Description

When setting up multiple warehouses and promoting to a stage which needs to update multiple images, it is not possible to promote to the stage the first time, since it fails when running the update image step. However, it will work to promote if promoting all of the required images - but there should be some kind of indication that the promotion didn't completely fail.

Screenshots

Steps to Reproduce

1. Create multiple warehouses that pull in different images
2. Setup a promotionTemplate like so:

   promotionTemplate:
   spec:
     steps:
       - config:
           checkout:
             - branch: main
               path: ./src
             - branch: deploy/prod
               create: true
               path: ./out
           repoURL: https://github.com/myowner/myrepo.git
         uses: git-clone
       - config:
           path: ./out
         uses: git-clear
       - as: update-image
         config:
           images:
             - fromOrigin:
                 kind: Warehouse
                 name: canary
               image: mycanaryrepo
             - fromOrigin:
                 kind: Warehouse
                 name: tester
               image: mytesterimage
           path: ./src/infrastructure/overlays/prod
         uses: kustomize-set-image
       - config:
           outPath: ./out
           path: ./src/infrastructure/overlays/prod
         uses: kustomize-build
       - as: commit
         config:
           messageFromSteps:
             - update-image
           path: ./out
         uses: git-commit
       - config:
           path: ./out
         uses: git-push
       - config:
           apps:
             - name: drive-canary-prod
               sources:
                 - desiredCommitFromStep: commit
                   repoURL: https://github.com/myowner/myrepo.git
         uses: argocd-update
   requestedFreight:
   - origin:
       kind: Warehouse
       name: canary
     sources:
       stages:
         - stg
   - origin:
       kind: Warehouse
       name: tester
     sources:
       stages:
         - stg

Version

0.9.1

[krancour]

We've been aware of this since "multi-pipelines" was introduced.

We tried hard to come up with some way to avoid this, but as long as Promotions promote a single piece of Freight at a time, this is unavoidable. We did weigh the possibility of Promotions being able to promote multiple pieces of Freight simultaneously, but found that the UX around that was pretty terrible.

Suffice it to say we're open to ideas.

but there should be some kind of indication that the promotion didn't completely fail.

I gather you're still using legacy promotion mechanisms and not the promotion steps introduced in v0.9.0? Promotion steps should be very clear about where in the process your error occurred.

In v1.0.0, failure to find an artifact among the Stage's (possibly many) Freight is a much more explicit error, which should improve the situation even further.

[hiddeco]

I think for certain promotion steps, we could theoretically make the presence of Freight which matches the selector optional via opt-in. I.e., "update everything you can for all I have, and if nothing matches — that's fine as well".

[kejne]

I'm using the new promotion steps so it was quite clear that the "other freight" would be needed as well to get things working properly. This is why I figured out to just try the other freight as well - however, it was a bit hard to convey this to the application teams trying it out as they would have to understand the promotion steps.

If it could be visualized somehow that the freight is still "under promotion" to the stage it would be cleared that the second freight also needs to be promoted in order for a successful promotion. Maybe a simple trailing hint in the error message when not finding an image for the steps that take arrays as input? Like: "have you promoted all required freights?"

[krancour]

however, it was a bit hard to convey this to the application teams trying it out as they would have to understand the promotion steps.

fwiw, we regard multi-pipelines as a bit of an advanced feature and perhaps take it for granted that someone going down this road understands Kargo quite well.

Maybe a simple trailing hint in the error message when not finding an image for the steps that take arrays as input? Like: "have you promoted all required freights?"

This is quite a good suggestion.