Function Scaling and Triggers

Scaling is one of the core features of a FaaS or Serverless platform.

OpenFunction defines function scaling in ScaleOptions and defines triggers to activate function scaling in Triggers

ScaleOptions

You can define unified function scale options for sync and async functions like below which will be valid for both sync and async functions:

apiVersion: core.openfunction.io/v1beta1
kind: Function
metadata:
  name: function-sample
spec:
  serving:
    scaleOptions:
      minReplicas: 0
      maxReplicas: 10

Usually simply defining minReplicas and maxReplicas is not enough for async functions. You can define seperate scale options for async functions like below which will override the minReplicas and maxReplicas.

You can find more details of async function scale options in KEDA ScaleObject Spec and KEDA ScaledJob Spec.

apiVersion: core.openfunction.io/v1beta1
kind: Function
metadata:
  name: function-sample
spec:
  serving:
    scaleOptions:
      keda:
        scaledObject:
          pollingInterval: 15
          minReplicaCount: 0
          maxReplicaCount: 10
          cooldownPeriod: 60
          advanced:
            horizontalPodAutoscalerConfig:
              behavior:
                scaleDown:
                  stabilizationWindowSeconds: 45
                  policies:
                  - type: Percent
                    value: 50
                    periodSeconds: 15
                scaleUp:
                  stabilizationWindowSeconds: 0

You can also set advanced scale options for Knative sync functions too which will override the minReplicas and maxReplicas.

You can find more details of the Knative sync function scale options here

apiVersion: core.openfunction.io/v1beta1
kind: Function
metadata:
  name: function-sample
spec:
  serving:
    scaleOptions:
      knative:
        autoscaling:
          autoscaling.knative.dev/min-scale: 0
          autoscaling.knative.dev/max-scale: 10
          autoscaling.knative.dev/initial-scale: "1"
          autoscaling.knative.dev/scale-down-delay: "0"
          autoscaling.knative.dev/window: "60s"
          autoscaling.knative.dev/panic-window-percentage: "10.0"
          autoscaling.knative.dev/metric: "concurrency"
          autoscaling.knative.dev/target: 100

Triggers

Triggers define how to activate function scaling for async functions. You can use triggers defined in all KEDA scalers as OpenFunction’s trigger spec.

Sync functions’ scaling is activated by various options of HTTP requests which are already defined in the previous ScaleOption section.

apiVersion: core.openfunction.io/v1beta1
kind: Function
metadata:
  name: function-sample
spec:
  serving:
    runtime: "async"
    triggers:
      - type: kafka
        metadata:
          topic: logs
          bootstrapServers: kafka-server-kafka-brokers.default.svc.cluster.local:9092
          consumerGroup: logs-handler
          lagThreshold: "20"