Experimental KEDA support for Knative Event Sources Autoscaling


STATUS	Experimental
Sponsoring WG	Eventing Sources

Warning: Still under development. Not meant for production deployment.

Design

To enable KEDA Autoscaling of Knative Event Sources (and other components in the future) there is a separate controller implemented, ie. no hard dependency in Knative. This contoller si watching for CustomResourcesDefinitions resources in the cluster, if there is installed a new CRD which is supported by this controller a new dynamic controller watching these resources is created.

Currently there is support for Kafka Source and AWS SQS Source. We also have experimental support for RabbitMQ Broker.

Annotations

User can enable and configure autoscaling on a particular Source or Broker by a set of annotations.

metadata:
  annotations:
    autoscaling.knative.dev/class: keda.autoscaling.knative.dev
    autoscaling.knative.dev/minScale: "0" 
    autoscaling.knative.dev/maxScale: "5" 
    keda.autoscaling.knative.dev/pollingInterval: "30" 
    keda.autoscaling.knative.dev/cooldownPeriod: "30" 

    # Kafka Source
    keda.autoscaling.knative.dev/kafkaLagThreshold: "10"

    # AWS SQS Source
    keda.autoscaling.knative.dev/awsSqsQueueLength: "5"

autoscaling.knative.dev/class: keda.autoscaling.knative.dev - needs to be specified on a Source to enable KEDA autoscaling
autoscaling.knative.dev/minScale - minimum number of replicas to scale down to. Default: 0
autoscaling.knative.dev/maxScale - maximum number of replicas to scale out to. Default: 50
keda.autoscaling.knative.dev/pollingInterval - interval in seconds KEDA uses to poll metrics. Default: 30
keda.autoscaling.knative.dev/cooldownPeriod - period of time in seconds KEDA waits until it scales down. Default: 300
keda.autoscaling.knative.dev/kafkaLagThreshold - only for Kafka Source, refers to the stream is lagging on the current consumer group. Default: 10
keda.autoscaling.knative.dev/awsSqsQueueLength - only for AWS SQS Source, refers to the target value for ApproximateNumberOfMessages in the SQS Queue. Default: 5
keda.autoscaling.knative.dev/rabbitMQQueueLength - only for AWS SQS Source, refers to the target value for number of messages in a RabbitMQ brokers trigger queue: 1

HOW TO

Install KEDA v2

It is needed to install KEDA v2, which is using different namespace for it's CRDs (keda.k8s.io -> keda.sh).

Currently there is development (Alpha) version of KEDA v2, to install it follow instructions on: https://github.com/kedacore/keda#how-can-i-try-keda-v2-beta-version

Confirm there are 2 pods running in keda namespace:

$ kubectl get pods -n keda
NAME                                      READY   STATUS    RESTARTS   AGE
keda-metrics-apiserver-7cf7765dc8-k9lnc   1/1     Running   0          5m2s
keda-operator-55658855fc-rc9rb            1/1     Running   0          5m3s

Install `eventing-autoscaler-keda` Controller

export KO_DOCKER_REPO=...
ko apply -f /config

Confirm there is 1 pod running in eventing-autoscaler-keda namespace:

$ kubectl get pods -n eventing-autoscaler-keda
NAME                          READY   STATUS    RESTARTS   AGE
controller-76fb8d6756-5f4vm   1/1     Running   0          21m

Example of Kafka Source autoscaled by KEDA

Set up Kafka Cluster, eg. use Strimzi operator
Install Knative Serving and Eventing
Install Knative Eventing Kafka Source
Create KafkaSource resource, with annotation autoscaling.knative.dev/class: keda.autoscaling.knative.dev. There are other KEDA related annotations, see the example:

apiVersion: sources.knative.dev/v1alpha1
kind: KafkaSource
metadata:
  name: kafka-source
  namespace: default
  annotations:
    autoscaling.knative.dev/class: keda.autoscaling.knative.dev
    autoscaling.knative.dev/minScale: "0" 
    autoscaling.knative.dev/maxScale: "5" 
    keda.autoscaling.knative.dev/pollingInterval: "30" 
    keda.autoscaling.knative.dev/cooldownPeriod: "30" 
    keda.autoscaling.knative.dev/kafkaLagThreshold: "10"
spec:
  consumerGroup: knative-group
  bootstrapServers: 
    - my-cluster-kafka-bootstrap.openshift-operators:9092 
  topics: 
    - test
  sink:
    ref:
      apiVersion: serving.knative.dev/v1
      kind: Service
      name: event-display

Check that ScaledObject was created for this KafkaSource:

$ kubectl get scaledobjects
NAME                                      SCALETARGETKIND      SCALETARGETNAME                                                 TRIGGERS   AUTHENTICATION   READY   ACTIVE   AGE
so-f87369e5-c320-4f44-b23a-8c535a523e3a   apps/v1.Deployment   kafkasource-kafka-source-f87369e5-c320-4f44-b23a-8c535a523e3a   kafka                       True    False     6m5s

Example of RabbitMQ Broker autoscaled by KEDA

Install Knative Serving and Eventing
Install RabbitMQ Broker
Install a Broker / Trigger and sources as directed in the above guide.
Enable the autoscaler by applying the KEDA patch:

kubectl patch broker default --type merge --patch '{"metadata": {"annotations": {"autoscaling.knative.dev/class": "keda.autoscaling.knative.dev"}}}'

Check that the scaled resources were created and are ready

vaikas-a01:eventing-autoscaler-keda vaikas$ kubectl get triggerauthentications
NAME                   PODIDENTITY   SECRET                  ENV
default-trigger-auth                 default-broker-rabbit
vaikas-a01:eventing-autoscaler-keda vaikas$ kubectl get scaledobjects
NAME           SCALETARGETKIND      SCALETARGETNAME           TRIGGERS   AUTHENTICATION         READY   ACTIVE   AGE
ping-trigger   apps/v1.Deployment   ping-trigger-dispatcher   rabbitmq   default-trigger-auth   True    True     14m

runzexia/eventing-autoscaler-keda