×

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 web console

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 +AddChannel.

  2. Select the type of Channel object that you want to create from the Type drop-down.

  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 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 by using the kn CLI.

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 (oc) 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
  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 Kafka 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. 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 (oc) 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
  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

  • After you have created a channel, create a subscription that allows event sinks to subscribe to channels and receive events.