High availability for Knative deployments - High availability configuration for Knative Serving | Serving

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

Configuring high availability replicas for Knative Serving

To specify three minimum replicas for the eligible deployment resources, set the value of the field spec.high-availability.replicas in the custom resource to 3.

Prerequisites

You have cluster administrator permissions on OpenShift Container Platform, or you have cluster or dedicated administrator permissions on Red Hat OpenShift Service on AWS or OpenShift Dedicated.
The OpenShift Serverless Operator and Knative Serving are installed on your cluster.

Procedure

In the OpenShift Container Platform 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:

Example YAML

apiVersion: operator.knative.dev/v1beta1
kind: KnativeServing
metadata:
  name: knative-serving
  namespace: knative-serving
spec:
  high-availability:
    replicas: 3

You can also specify the number of replicas for a specific workload.

Workload-specific configuration overrides the global setting for Knative Serving.

Example YAML

apiVersion: operator.knative.dev/v1beta1
kind: KnativeServing
metadata:
  name: knative-serving
  namespace: knative-serving
spec:
  high-availability:
    replicas: 3
  workloads:
  - name: webhook
    replicas: 4

Verify that the high availability limits are respected:

Example command

$ oc get hpa -n knative-serving

Example output

NAME        REFERENCE              TARGETS   MINPODS   MAXPODS   REPLICAS   AGE
activator   Deployment/activator   0%/100%   3         22        3          2m24s
webhook     Deployment/webhook     2%/100%   4         8         4          2m23s

Overriding disruption budgets

A Pod Disruption Budget (PDB) is a standard feature of Kubernetes APIs that helps limit the disruption to an application when its pods need to be rescheduled for maintenance reasons.

Procedure

Override the default PDB for a specific resource by modifying the minAvailable configuration value in the KnativeServing custom resource (CR).

Example PDB with a minAvailable seting of 70%

apiVersion: operator.knative.dev/v1beta1
kind: KnativeServing
metadata:
 name: knative-serving
 namespace: knative-serving
spec:
 podDisruptionBudgets:
 - name: activator-pdb
   minAvailable: 70%

If you disable high-availability, for example, by changing the high-availability.replicas value to 1, make sure you also update the corresponding PDB minAvailable value to 0. Otherwise, the pod disruption budget prevents automatic cluster or Operator updates.