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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 readily available. This controller takes 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 called the leader.

Configuring high availability replicas for Knative Serving

High availability (HA) is available by default for the Knative Serving activator, autoscaler, autoscaler-hpa, controller, webhook, kourier-control, and kourier-gateway components, which are configured to have two replicas each by default. You can change the number of replicas for these components by modifying the spec.high-availability.replicas value in the KnativeServing custom resource (CR).

Prerequisites
  • 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.

  • You have logged into the web console.

Procedure
  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.

    Knative Serving YAML
  5. Modify the number of replicas in the KnativeServing CR:

    Example YAML
    apiVersion: operator.knative.dev/v1alpha1
    kind: KnativeServing
    metadata:
      name: knative-serving
      namespace: knative-serving
    spec:
      high-availability:
        replicas: 3

Configuring high availability replicas for Knative Eventing

High availability (HA) is available by default for the Knative Eventing eventing-controller, eventing-webhook, imc-controller, imc-dispatcher, mt-broker-controller, and sugar-controller components, which are configured to have two replicas each by default. You can change the number of replicas for these components by modifying the spec.high-availability.replicas value in the KnativeEventing custom resource (CR).

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.

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

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

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

  2. Select the knative-eventing namespace.

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

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