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k8s deployer: WaitForDeploymentAvailable errors on a 0-replica Deployment (keda scale-to-zero redeploy)

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@Elvand-Lie がすでに取り組んでいます。

2026年10月11日 から。

  • #4075 @Elvand-Lie による — オープン

評価

難易度
3/5
見積もり時間
1〜2日
初心者へのやさしさ
72/100
issue の種類
バグ
明瞭さ
おおむね明確
活発さ
活発
技術スタック
go, kubernetes
領域
infrastructure

調査の方向性

Start by reading WaitForDeploymentAvailable and checkIfDeploymentIsAvailable in pkg/k8s/wait.go, then compare how deployments are applied in pkg/k8s/deployer.go. Add coverage for the zero-replica case and verify the existing wait behavior remains intact; a KEDA-backed redeploy can provide the integration repro if needed.

索引モデルが issue の本文から書いたものです。

説明

Summary

WaitForDeploymentAvailable (pkg/k8s/wait.go) can fail a redeploy with
could not find current pod-template-hash for deployment <name> when the live
Deployment has 0 desired replicas. This is reachable today via the keda
(HTTP-scaler) deployer, whose ScaledObject scales idle functions down to zero.

Note: this is reasoned from the code, not yet reproduced (it's a timing race).
Filing so the analysis is tracked; repro TBD.

Details

WaitForDeploymentAvailable re-fetches the live Deployment on every poll tick:

deployment, err := clientset.AppsV1().Deployments(namespace).Get(ctx, deploymentName, metav1.GetOptions{})
...
return checkIfDeploymentIsAvailable(ctx, clientset, deployment)

checkIfDeploymentIsAvailable finds the active ReplicaSet by looking for one with
*rs.Spec.Replicas > 0. A Deployment sitting at 0 desired replicas has no such
ReplicaSet, so currentPodTemplateHash stays empty and the function returns an error
(pkg/k8s/wait.go):

if currentPodTemplateHash == "" {
    return false, fmt.Errorf("could not find current pod-template-hash for deployment %s", deployment.Name)
}

The func deployer itself always applies replicas >= 1 (pkg/k8s/deployer.go), so
it never creates a 0-replica Deployment. But because the wait inspects live state,
reachability is governed by what KEDA does during the wait, not by what func wrote:

  1. An idle keda-HTTP function has been scaled to 0 replicas by KEDA.
  2. User redeploys. func applies the Deployment with replicas: 1, then starts polling.
  3. If the KEDA controller reasserts 0 replicas on the live Deployment before the poll
    observes it as ready, the live fetch returns spec.replicas == 0, and the wait
    returns the pod-template-hash error — failing the redeploy.
Suggested fix

Short-circuit when there is nothing to wait for:

desiredReplicas := *deployment.Spec.Replicas
if desiredReplicas == 0 {
    return true, nil // no replicas desired; nothing to wait for
}

This also unblocks any future spec-level scale-to-zero on the raw/keda Deployment.

Notes
  • Reasoned from code; not reproduced. A repro needs a cluster with KEDA and an idle,
    scaled-to-zero HTTP function being redeployed.
  • Fix is small and self-contained but likely wants a repro or unit test first, hence
    filing as an issue rather than an immediate PR.
主要言語
Go
スター
365
フォーク
224
平均マージ
1日 13時間
マージ済み PR（30日）
17

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