Upgrading to Flagger built on main (commit id #133fdec) causes canary rollouts when no change in deployments

[jdgeisler]

Describe the bug

I've been working on an MR for issue https://github.com/fluxcd/flagger/issues/1646 and ran into this following bug when testing Flagger in my personal kubernetes cluster. I've also reached out in the slack channel here

When building my own docker image from main (commit id #133fdec), I am seeing canary rollouts triggered even though there were no changes to my canary deployment spec. As soon as Flagger was upgraded to this image, the canaries detected a new revision and began the analysis.

{"level":"info","ts":"2024-06-25T15:01:58.687Z","caller":"controller/controller.go:307","msg":"Synced fortio/fortio-server-deployment-2"}
{"level":"info","ts":"2024-06-25T15:02:08.802Z","caller":"controller/events.go:33","msg":"New revision detected! Scaling up fortio-server-deployment-2.fortio","canary":"fortio-server-deployment-2.fortio"}
{"level":"info","ts":"2024-06-25T15:02:38.791Z","caller":"controller/events.go:33","msg":"Starting canary analysis for fortio-server-deployment-2.fortio","canary":"fortio-server-deployment-2.fortio"}

To confirm, I also compared 1:1 the deployment spec and nothing changed. This should mean the calculated hash is the same, but for some reason the lastAppliedSpec hash in the canary was different.

No matter what, the docker image from v1.37 results in this hash in the canary
lastAppliedSpec: 5454669676
lastPromotedSpec: 5454669676

Then, when upgraded to the image built from main, it results in this new hash in the canary
lastAppliedSpec: 5475b95f98
lastPromotedSpec: 5475b95f98

For a sanity check, I also built a custom image from the last tag v1.37, and confirmed the canary analysis is not triggered when upgraded. I also confirmed that the hash remains the same.

To Reproduce

1. Build docker image from main (commit id #133fdec)
2. Upgrade Flagger to the new image in a Kubernetes cluster with canary deployments
3. See that the canary analysis is triggered

Expected behavior

It is expected that upgrading Flagger does not cause canary rollouts to be triggered if nothing changes in the canary deployments.

Additional context

• Flagger version: main (commit id #133fdec)
• Kubernetes version: 1.27
• Service Mesh provider: istio 1.19.7