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Creating channels

Channels are custom resources that define a single event-forwarding and persistence layer. After events have been sent to a channel from an event source or producer, these events can be sent to multiple Knative services or other sinks by using a subscription.

Channel workflow overview

You can create channels by instantiating a supported Channel object, and configure re-delivery attempts by modifying the delivery spec in a Subscription object.

Creating a channel by using the Administrator perspective

After Knative Eventing is installed on your cluster, you can create a channel by using the Administrator perspective.

Prerequisites

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

  • You have logged in to the web console and are in the Administrator perspective.

  • 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.

Procedure

  1. In the Administrator perspective of the OpenShift Container Platform web console, navigate to Serverless → Eventing.

  2. In the Create list, select Channel. You will be directed to the Channel page.

  3. Select the type of Channel object that you want to create in the Type list.

    Currently only InMemoryChannel channel objects are supported by default. Knative channels for Apache Kafka are available if you have installed the Knative broker implementation for Apache Kafka on OpenShift Serverless.

  4. Click Create.

Creating a channel by using the Developer perspective

Using the OpenShift Container Platform web console provides a streamlined and intuitive user interface to create a channel. After Knative Eventing is installed on your cluster, you can create a channel by using the web console.

Prerequisites

  • You have logged in to the OpenShift Container Platform web console.

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

  • You have created a project or have access to a project with the appropriate roles and permissions to create applications and other workloads in OpenShift Container Platform.

Procedure

  1. In the Developer perspective, navigate to +Add → Channel.

  2. Select the type of Channel object that you want to create in the Type list.

  3. Click Create.

Verification

  • Confirm that the channel now exists by navigating to the Topology page.

    View the channel in the Topology view

Creating a channel by using the Knative CLI

Using the Knative (kn) CLI to create channels provides a more streamlined and intuitive user interface than modifying YAML files directly. You can use the kn channel create command to create a channel.

Prerequisites

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

  • You have installed the Knative (kn) CLI.

  • You have created a project or have access to a project with the appropriate roles and permissions to create applications and other workloads in OpenShift Container Platform.

Procedure

  • Create a channel:

    $ kn channel create <channel_name> --type <channel_type>

    The channel type is optional, but where specified, must be given in the format Group:Version:Kind. For example, you can create an InMemoryChannel object:

    $ kn channel create mychannel --type messaging.knative.dev:v1:InMemoryChannel
    Example output
    Channel 'mychannel' created in namespace 'default'.
Verification

  • To confirm that the channel now exists, list the existing channels and inspect the output:

    $ kn channel list
    Example output
    kn channel list
NAME        TYPE              URL                                                     AGE   READY   REASON
mychannel   InMemoryChannel   http://mychannel-kn-channel.default.svc.cluster.local   93s   True
Deleting a channel

  • Delete a channel:

    $ kn channel delete <channel_name>

Creating a default implementation channel by using YAML

Creating Knative resources by using YAML files uses a declarative API, which enables you to describe channels declaratively and in a reproducible manner. To create a serverless channel by using YAML, you must create a YAML file that defines a Channel object, then apply it by using the oc apply command.

Prerequisites

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

  • Install the OpenShift CLI (oc).

  • You have created a project or have access to a project with the appropriate roles and permissions to create applications and other workloads in OpenShift Container Platform.

Procedure

  1. Create a Channel object as a YAML file:

    apiVersion: messaging.knative.dev/v1
kind: Channel
metadata:
  name: example-channel
  namespace: default

  2. Apply the YAML file:

    $ oc apply -f <filename>

Creating a channel for Apache Kafka by using YAML

Creating Knative resources by using YAML files uses a declarative API, which enables you to describe channels declaratively and in a reproducible manner. You can create a Knative Eventing channel that is backed by Kafka topics by creating a Kafka channel. To create a Kafka channel by using YAML, you must create a YAML file that defines a KafkaChannel object, then apply it by using the oc apply command.

Prerequisites

  • The OpenShift Serverless Operator, Knative Eventing, and the KnativeKafka custom resource are installed on your OpenShift Container Platform cluster.

  • Install the OpenShift CLI (oc).

  • You have created a project or have access to a project with the appropriate roles and permissions to create applications and other workloads in OpenShift Container Platform.

Procedure

  1. Create a KafkaChannel object as a YAML file:

    apiVersion: messaging.knative.dev/v1beta1
kind: KafkaChannel
metadata:
  name: example-channel
  namespace: default
spec:
  numPartitions: 3
  replicationFactor: 1

    Only the v1beta1 version of the API for KafkaChannel objects on OpenShift Serverless is supported. Do not use the v1alpha1 version of this API, as this version is now deprecated.

  2. Apply the KafkaChannel YAML file:

    $ oc apply -f <filename>

Next steps