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Chapter 10. Tuning eventing configuration

10.1. Overriding Knative Eventing system deployment configurations
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You can override the default configurations for some specific deployments by modifying the workloads spec in the KnativeEventing custom resource (CR). Currently, overriding default configuration settings is supported for the eventing-controller, eventing-webhook, and imc-controller fields, as well as for the readiness and liveness fields for probes.

Important

The replicas spec cannot override the number of replicas for deployments that use the Horizontal Pod Autoscaler (HPA), and does not work for the eventing-webhook deployment.

Note

You can only override probes that are defined in the deployment by default.

10.1.1. Overriding deployment configurations
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Currently, overriding default configuration settings is supported for the eventing-controller, eventing-webhook, and imc-controller fields, as well as for the readiness and liveness fields for probes.

Important

The replicas spec cannot override the number of replicas for deployments that use the Horizontal Pod Autoscaler (HPA), and does not work for the eventing-webhook deployment.

In the following example, a KnativeEventing CR overrides the eventing-controller deployment so that:

  • The readiness probe timeout eventing-controller is set to be 10 seconds.
  • The deployment has specified CPU and memory resource limits.
  • The deployment has 3 replicas.
  • The example-label: label label is added.
  • The example-annotation: annotation annotation is added.
  • The nodeSelector field is set to select nodes with the disktype: hdd label.

KnativeEventing CR example

apiVersion: operator.knative.dev/v1beta1
kind: KnativeEventing
metadata:
  name: knative-eventing
  namespace: knative-eventing
spec:
  workloads:
  - name: eventing-controller
    readinessProbes:
1 

      - container: controller
        timeoutSeconds: 10
    resources:
    - container: eventing-controller
      requests:
        cpu: 300m
        memory: 100Mi
      limits:
        cpu: 1000m
        memory: 250Mi
    replicas: 3
    labels:
      example-label: label
    annotations:
      example-annotation: annotation
    nodeSelector:
      disktype: hdd
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1
You can use the readiness and liveness probe overrides to override all fields of a probe in a container of a deployment as specified in the Kubernetes API except for the fields related to the probe handler: exec, grpc, httpGet, and tcpSocket.
Note

The KnativeEventing CR label and annotation settings override the deployment’s labels and annotations for both the deployment itself and the resulting pods.

10.1.2. Modifying consumer group IDs and topic names
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You can change templates for generating consumer group IDs and topic names used by your triggers, brokers, and channels.

Prerequisites

  • You have cluster or dedicated administrator permissions on OpenShift Container Platform.
  • The OpenShift Serverless Operator, Knative Eventing, and the KnativeKafka custom resource (CR) are installed on your OpenShift Container Platform cluster.
  • You have created a project or have access to a project that has the appropriate roles and permissions to create applications and other workloads in OpenShift Container Platform.
  • You have installed the OpenShift CLI (oc).

Procedure

  1. To change templates for generating consumer group IDs and topic names used by your triggers, brokers, and channels, modify the KnativeKafka resource: 

    apiVersion: v1
kind: KnativeKafka
metadata:
  name: knative-kafka
  namespace: knative-eventing
# ...
spec:
  config:
    config-kafka-features:
      triggers.consumergroup.template: <template>
    1 
    
      brokers.topic.template: <template>
    2 
    
      channels.topic.template: <template>
    3
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    1
    The template for generating the consumer group ID used by your triggers. Use a valid Go text/template value. Defaults to "knative-trigger-{{ .Namespace }}-{{ .Name }}".
    2
    The template for generating Kafka topic names used by your brokers. Use a valid Go text/template value. Defaults to "knative-broker-{{ .Namespace }}-{{ .Name }}".
    3
    The template for generating Kafka topic names used by your channels. Use a valid Go text/template value. Defaults to "messaging-kafka.{{ .Namespace }}.{{ .Name }}".

    Example template configuration

    apiVersion: v1
kind: KnativeKafka
metadata:
  name: knative-kafka
  namespace: knative-eventing
# ...
spec:
  config:
    config-kafka-features:
      triggers.consumergroup.template: "{% raw %}"knative-trigger-{{ .Namespace }}-{{ .Name }}-{{ .annotations.my-annotation }}"{% endraw %}"
      brokers.topic.template: "{% raw %}"knative-broker-{{ .Namespace }}-{{ .Name }}-{{ .annotations.my-annotation }}"{% endraw %}"
      channels.topic.template: "{% raw %}"messaging-kafka.{{ .Namespace }}.{{ .Name }}-{{ .annotations.my-annotation }}"{% endraw %}"
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  2. Apply the KnativeKafka YAML file: 

    $ oc apply -f <knative_kafka_filename>
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10.2. High availability
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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.

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.

10.2.1. Configuring high availability replicas for Knative Eventing
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High availability (HA) is available by default for the Knative Eventing eventing-controller, eventing-webhook, imc-controller, imc-dispatcher, and mt-broker-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).

Note

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 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 Eventing are installed on your cluster.

Procedure

  1. In the OpenShift Container Platform web console, navigate to OperatorHub Installed 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.

  5. Modify the number of replicas in the KnativeEventing CR:

    Example YAML

    apiVersion: operator.knative.dev/v1beta1
kind: KnativeEventing
metadata:
  name: knative-eventing
  namespace: knative-eventing
spec:
  high-availability:
    replicas: 3
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  6. You can also specify the number of replicas for a specific workload.

    Note

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

    Example YAML

    apiVersion: operator.knative.dev/v1beta1
kind: KnativeEventing
metadata:
  name: knative-eventing
  namespace: knative-eventing
spec:
  high-availability:
    replicas: 3
  workloads:
  - name: mt-broker-filter
    replicas: 3
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  7. Verify that the high availability limits are respected:

    Example command

    $ oc get hpa -n knative-eventing
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    Example output

    NAME                 REFERENCE                      TARGETS   MINPODS   MAXPODS   REPLICAS   AGE
broker-filter-hpa    Deployment/mt-broker-filter    1%/70%    3         12        3          112s
broker-ingress-hpa   Deployment/mt-broker-ingress   1%/70%    3         12        3          112s
eventing-webhook     Deployment/eventing-webhook    4%/100%   3         7         3          115s
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High availability (HA) is available by default for the Knative broker implementation for Apache Kafka components kafka-controller and kafka-webhook-eventing, which are configured to have two each replicas by default. You can change the number of replicas for these components by modifying the spec.high-availability.replicas value in the KnativeKafka custom resource (CR).

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 broker for Apache Kafka are installed on your cluster.

Procedure

  1. In the OpenShift Container Platform web console, navigate to OperatorHub Installed Operators.
  2. Select the knative-eventing namespace.
  3. Click Knative Kafka in the list of Provided APIs for the OpenShift Serverless Operator to go to the Knative Kafka tab.
  4. Click knative-kafka, then go to the YAML tab in the knative-kafka page.

  5. Modify the number of replicas in the KnativeKafka CR:

    Example YAML

    apiVersion: operator.serverless.openshift.io/v1alpha1
kind: KnativeKafka
metadata:
  name: knative-kafka
  namespace: knative-eventing
spec:
  high-availability:
    replicas: 3
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10.2.3. Overriding disruption budgets
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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 KnativeEventing custom resource (CR).

Example PDB with a minAvailable seting of 70%

apiVersion: operator.knative.dev/v1beta1
kind: KnativeEventing
metadata:
 name: knative-eventing
 namespace: knative-eventing
spec:
 podDisruptionBudgets:
 - name: eventing-webhook
   minAvailable: 70%
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Note

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.

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