High availability (HA) is a standard feature of Kubernetes APIs that helps to ensure that APIs stay operational if a disruption occurs. In an HA deployment, if an active controller crashes or is deleted, another controller is available to take over processing of the APIs that were being serviced by the controller that is now unavailable.

HA in OpenShift Serverless is available through leader election, which is enabled by default after the Knative Serving or Eventing control plane is installed.

When using a leader election HA pattern, instances of controllers are already scheduled and running inside the cluster before they are required. These controller instances compete to use a shared resource, known as the leader election lock. The instance of the controller that has access to the leader election lock resource at any given time is referred to as the leader.

Configuring high availability replicas on OpenShift Serverless

High availability (HA) functionality is available by default on OpenShift Serverless for Knative Serving, Knative Eventing, and Knative Kafka. These are the components scaled for each of them:

  • Knative Serving: activator, autoscaler, autoscaler-hpa, controller, webhook, kourier-control, kourier-gateway.

  • Knative Eventing: eventing-controller, eventing-webhook, imc-controller, imc-dispatcher, mt-broker-controller, sugar-controller.

  • Knative Kafka: kafka-ch-controller, kafka-controller-manager, kafka-webhook.

These components are configured with two replicas by default.

For Knative Eventing, the mt-broker-filter and mt-broker-ingress deployments are not scaled by HA. If multiple deployments are needed, scale these components manually.

You modify the number of replicas that are created per component by changing the configuration of spec.high-availability.replicas in the KnativeServing custom resource (CR), the KnativeEventing CR, or the KnativeKafka CR.

Configuring high availability replicas for Serving

You can scale Knative Serving components by modifying the spec.high-availability.replicas value in the KnativeServing custom resource.

  • You have access to an OpenShift Container Platform cluster with cluster administrator permissions.

  • The OpenShift Serverless Operator and Knative Serving are installed on your cluster.

  1. In the OpenShift Container Platform web console Administrator perspective, navigate to OperatorHubInstalled Operators.

  2. Select the knative-serving namespace.

  3. Click Knative Serving in the list of Provided APIs for the OpenShift Serverless Operator to go to the Knative Serving tab.

  4. Click knative-serving, then go to the YAML tab in the knative-serving page.