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.
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.
You can scale Knative Serving components by modifying the spec.high-availability.replicas
value in the KnativeServing
custom resource (CR).
You have access to an OpenShift Dedicated account with cluster administrator or dedicated administrator access.
The OpenShift Serverless Operator and Knative Serving are installed on your cluster.
In the OpenShift Dedicated web console Administrator perspective, navigate to OperatorHub → Installed Operators.
Select the knative-serving
namespace.
Click Knative Serving in the list of Provided APIs for the OpenShift Serverless Operator to go to the Knative Serving tab.
Click knative-serving, then go to the YAML tab in the knative-serving page.
Modify the number of replicas in the KnativeServing
CR:
apiVersion: operator.knative.dev/v1alpha1
kind: KnativeServing
metadata:
name: knative-serving
namespace: knative-serving
spec:
high-availability:
replicas: 3 (1)
1 | Sets the number of replicas to 3 .
|
You can scale Knative Eventing components by modifying the spec.high-availability.replicas
value in the KnativeEventing
custom resource (CR).
You have access to an OpenShift Dedicated account with cluster administrator or dedicated administrator access.
The OpenShift Serverless Operator and Knative Eventing are installed on your cluster.
In the OpenShift Dedicated web console Administrator perspective, navigate to OperatorHub → Installed Operators.
Select the knative-eventing
namespace.
Click Knative Eventing in the list of Provided APIs for the OpenShift Serverless Operator to go to the Knative Eventing tab.
Click knative-eventing, then go to the YAML tab in the knative-eventing page.
Modify the number of replicas in the KnativeEventing
CR:
apiVersion: operator.knative.dev/v1alpha1
kind: KnativeEventing
metadata:
name: knative-eventing
namespace: knative-eventing
spec:
high-availability:
replicas: 3 (1)
1 | Sets the number of replicas to 3 .
|
You can scale Knative Kafka components by modifying the spec.high-availability.replicas
value in the KnativeKafka
custom resource (CR).
You have access to an OpenShift Dedicated account with cluster administrator or dedicated administrator access.
The OpenShift Serverless Operator and Knative Kafka are installed on your cluster.
In the OpenShift Dedicated web console Administrator perspective, navigate to OperatorHub → Installed Operators.
Select the knative-eventing
namespace.
Click Knative Kafka in the list of Provided APIs for the OpenShift Serverless Operator to go to the Knative Kafka tab.
Click knative-kafka, then go to the YAML tab in the knative-kafka page.
Modify the number of replicas in the KnativeKafka
CR:
apiVersion: operator.serverless.openshift.io/v1alpha1
kind: KnativeKafka
metadata:
name: knative-kafka
namespace: knative-eventing
spec:
high-availability:
replicas: 3 (1)
1 | Sets the number of replicas to 3 .
|