Supported Autoscaler types¶

Knative Serving supports the implementation of Knative Pod Autoscaler (KPA) and Kubernetes' Horizontal Pod Autoscaler (HPA). This topic lists the features and limitations of each of these Autoscalers, as well as how to configure them.

For how to install HPA, see Install optional Serving extensions.

Knative Pod Autoscaler (KPA)¶

• Part of the Knative Serving core and enabled by default once Knative Serving is installed.
• Supports scale to zero functionality.
• Does not support CPU-based autoscaling.

Horizontal Pod Autoscaler (HPA)¶

• Not part of the Knative Serving core, and you must install Knative Serving first.
• Does not support scale to zero functionality.
• Supports CPU-based autoscaling.

Configuring the Autoscaler implementation¶

The type of Autoscaler implementation (KPA or HPA) can be configured by using the class annotation.

• Global settings key: pod-autoscaler-class
• Per-revision annotation key: autoscaling.knative.dev/class
• Possible values: "kpa.autoscaling.knative.dev" or "hpa.autoscaling.knative.dev"
• Default: "kpa.autoscaling.knative.dev"

Example:

apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: helloworld-go
  namespace: default
spec:
  template:
    metadata:
      annotations:
        autoscaling.knative.dev/class: "kpa.autoscaling.knative.dev"
    spec:
      containers:
        - image: ghcr.io/knative/helloworld-go:latest

apiVersion: v1
kind: ConfigMap
metadata:
 name: config-autoscaler
 namespace: knative-serving
data:
 pod-autoscaler-class: "kpa.autoscaling.knative.dev"

apiVersion: operator.knative.dev/v1alpha1
kind: KnativeServing
metadata:
  name: knative-serving
spec:
  config:
    autoscaler:
      pod-autoscaler-class: "kpa.autoscaling.knative.dev"

Global versus per-revision settings¶

Configuring for autoscaling in Knative can be set using either global or per-revision settings.

1. If no per-revision autoscaling settings are specified, the global settings will be used.
2. If per-revision settings are specified, these will override the global settings when both types of settings exist.

Global settings¶

Global settings for autoscaling are configured using the config-autoscaler ConfigMap. If you installed Knative Serving using the Operator, you can set global configuration settings in the spec.config.autoscaler ConfigMap, located in the KnativeServing custom resource (CR).

Example of the default autoscaling ConfigMap¶

apiVersion: v1
kind: ConfigMap
metadata:
 name: config-autoscaler
 namespace: knative-serving
data:
 container-concurrency-target-default: "100"
 container-concurrency-target-percentage: "0.7"
 enable-scale-to-zero: "true"
 max-scale-up-rate: "1000"
 max-scale-down-rate: "2"
 panic-window-percentage: "10"
 panic-threshold-percentage: "200"
 scale-to-zero-grace-period: "30s"
 scale-to-zero-pod-retention-period: "0s"
 stable-window: "60s"
 target-burst-capacity: "200"
 requests-per-second-target-default: "200"

Per-revision settings¶

Per-revision settings for autoscaling are configured by adding annotations to a revision.

Example:

apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: helloworld-go
  namespace: default
spec:
  template:
    metadata:
      annotations:
        autoscaling.knative.dev/target: "70"