Configuring scale to zero¶

Warning

Scale to zero can only be enabled if you are using the KnativePodAutoscaler (KPA), and can only be configured globally. For more information about using KPA or global configuration, see the documentation on Supported Autoscaler types.

Global defaults and constraints below are defined in v1.24 autoscaler configuration; per-revision retention constraints are defined in annotation validation.

Enable scale to zero¶

The scale to zero value controls whether Knative allows replicas to scale down to zero (if set to true), or stop at 1 replica if set to false.

Note

For more information about scale bounds configuration per Revision, see the documentation on Configuring scale bounds.

Global key: enable-scale-to-zero
Per-revision annotation key: No per-revision setting.
Possible values: boolean
Default: true

Example:

Global (ConfigMap)Global (Operator)

apiVersion: v1
kind: ConfigMap
metadata:
 name: config-autoscaler
 namespace: knative-serving
data:
 enable-scale-to-zero: "false"

apiVersion: operator.knative.dev/v1beta1
kind: KnativeServing
metadata:
  name: knative-serving
spec:
  config:
    autoscaler:
      enable-scale-to-zero: "false"

Scale to zero grace period¶

This setting specifies an upper bound time limit that the system will wait internally for scale-from-zero machinery to be in place before the last replica is removed.

Warning

This is a value that controls how long internal network programming is allowed to take, and should only be adjusted if you experience issues with requests being dropped while a Revision is scaling to zero Replicas.

This setting does not adjust how long the last replica will be kept after traffic ends, and it does not guarantee that the replica will actually be kept for this entire duration.

Global key: scale-to-zero-grace-period
Per-revision annotation key: n/a
Possible values: Positive duration
Default: 30s

Example:

Global (ConfigMap)Global (Operator)

apiVersion: v1
kind: ConfigMap
metadata:
 name: config-autoscaler
 namespace: knative-serving
data:
 scale-to-zero-grace-period: "40s"

apiVersion: operator.knative.dev/v1beta1
kind: KnativeServing
metadata:
  name: knative-serving
spec:
  config:
    autoscaler:
      scale-to-zero-grace-period: "40s"

Scale to zero last pod retention period¶

The scale-to-zero-pod-retention-period flag determines the minimum amount of time that the last pod will remain active after the Autoscaler decides to scale pods to zero.

Unlike this minimum retention interval, scale-to-zero-grace-period bounds the wait for network programming. It is not a promise about how long the last pod remains active after traffic ends.

Global key: scale-to-zero-pod-retention-period
Per-revision annotation key: autoscaling.knative.dev/scale-to-zero-pod-retention-period
Possible values: Nonnegative duration. The per-revision annotation is limited to 1h; the global parser does not impose that maximum.
Default: 0s

Example:

Per RevisionGlobal (ConfigMap)Global (Operator)

apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: helloworld-go
  namespace: default
spec:
  template:
    metadata:
      annotations:
        autoscaling.knative.dev/scale-to-zero-pod-retention-period: "1m5s"
    spec:
      containers:
        - image: ghcr.io/knative/helloworld-go:latest

apiVersion: v1
kind: ConfigMap
metadata:
 name: config-autoscaler
 namespace: knative-serving
data:
 scale-to-zero-pod-retention-period: "42s"

apiVersion: operator.knative.dev/v1beta1
kind: KnativeServing
metadata:
  name: knative-serving
spec:
  config:
    autoscaler:
      scale-to-zero-pod-retention-period: "42s"