Global scale-down-delay setting ignored

[harrymilne]

What version of Knative?

0.14.x
0.16.x

Expected Behavior

A delay before Knative Pods are scaled in

Actual Behavior

Behaviour does not change before and after setting the scale-down-delay in the config-autoscaler ConfigMap via the Knative Operator, Pods are still scaled in without delay

Steps to Reproduce the Problem

• Create scale-to-zero Knative Service
• Set global scale-down-delay to 1h or anything
• Run enough requests to trigger Revision scale out
• Monitor as Pods only stay around as long as the traffic exists

[skonto]

Hi @harrymilne,

I tried to reproduce this, when installing with Serving yamls but with no result, same with operator.
You can try the operator with the following serving CR:

apiVersion: operator.knative.dev/v1beta1
kind: KnativeServing
metadata:
  name: knative-serving
spec:
  ingress:
    kourier:
      enabled: true
  config:
    logging:
      loglevel.autoscaler: "debug"
    network:
      ingress-class: "kourier.ingress.networking.knative.dev"
    autoscaler:
      scale-down-delay: "15m"

If you set loglevel.autoscaler: debug in cm config-autoscaler you should see then in autoscaler's log:

kubectl logs autoscaler-6c7bf97997-tdlxd -n knative-serving | grep Delaying
...
{"severity":"DEBUG","timestamp":"2024-11-18T11:39:31.899586353Z","logger":"autoscaler","caller":"scaling/autoscaler.go:261","message":"Delaying scale to 0, staying at 1","commit":"6a27004","knative.dev/key":"default/autoscale-go-00001"}

Also when you update the cm via the Serving Cr you should get in the autoscaler pod logs:

{"severity":"DEBUG","timestamp":"2024-11-18T13:08:38.839831791Z","logger":"autoscaler.config-store","caller":"configmap/store.go:155","message":"autoscaler config \"config-autoscaler\" config was added or updated: &autoscalerconfig.Config{EnableScaleToZero:true, ContainerConcurrencyTargetFraction:0.7, ContainerConcurrencyTargetDefault:100, TargetUtilization:0.7, RPSTargetDefault:200, TargetBurstCapacity:211, ActivatorCapacity:100, AllowZeroInitialScale:false, InitialScale:1, MinScale:0, MaxScale:0, MaxScaleLimit:0, MaxScaleUpRate:1000, MaxScaleDownRate:2, StableWindow:60000000000, PanicWindowPercentage:10, PanicThresholdPercentage:200, ScaleToZeroGracePeriod:30000000000, ScaleToZeroPodRetentionPeriod:0, ScaleDownDelay:900000000000, PodAutoscalerClass:\"kpa.autoscaling.knative.dev\"}","commit":"6a27004"}

With a scaleDownDelay=15m the pod did scale down after ~15min:

kubectl get po 
NAME                                             READY   STATUS    RESTARTS   AGE
autoscale-go-00001-deployment-6f564fbb6c-r4nb9   2/2     Running   0          16m
kubectl get po 
NAME                                             READY   STATUS        RESTARTS   AGE
autoscale-go-00001-deployment-6f564fbb6c-r4nb9   2/2     Terminating   0          16m

I tested with version 1.16.