Chapter 7. Subscriptions

Prerequisites

• You have installed the OpenShift Serverless Operator, Knative Serving, and Knative Eventing on your OpenShift Container Platform cluster.
• You have logged in to the web console.
• You have created an event sink, such as a Knative service, and a channel.
• You have created a project or have access to a project with the appropriate roles and privileges to create applications and other workloads in OpenShift Container Platform.

Verification

• After you create the subscription, the Topology view shows it as a line that connects the channel to the service.

  

Prerequisites

• You have installed the OpenShift Serverless Operator and Knative Eventing 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

• Create a Subscription object:

  • Create a YAML file and copy the following sample code into it:

    apiVersion: messaging.knative.dev/v1
    kind: Subscription
    metadata:
      name: my-subscription
      namespace: default
    spec:
      channel:
        apiVersion: messaging.knative.dev/v1
        kind: Channel
        name: example-channel
      delivery:
        deadLetterSink:
          ref:
            apiVersion: serving.knative.dev/v1
            kind: Service
            name: error-handler
      subscriber:
        ref:
          apiVersion: serving.knative.dev/v1
          kind: Service
          name: event-display

    • name: my-subscription: Name of the subscription.
    • spec.channel: Configuration settings for the channel that the subscription connects to.
    • spec.delivery: Configuration settings for event delivery. These settings define how the subscription handles events that the subscriber cannot receive. When you configure this option, the system sends failed events to the deadLetterSink. The system drops the event, does not try redelivery, and logs an error. The deadLetterSink value must be a Destination.
    • spec.subscriber: Configuration settings for the subscriber. The subscriber is the event sink that receives events from the channel.

  • Apply the YAML file by running the following command:

    $ oc apply -f <filename>

Prerequisites

• You have installed the OpenShift Serverless Operator and Knative Eventing on your OpenShift Container Platform 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 subscription to connect a sink to a channel:

  $ kn subscription create <subscription_name> \
    --channel <group:version:kind>:<channel_name> \
    --sink <sink_prefix>:<sink_name> \
    --sink-dead-letter <sink_prefix>:<sink_name>

  You get an output similar to the following example command:

  $ kn subscription create mysubscription --channel mychannel --sink ksvc:event-display

  You get an output similar to the following example:

  Subscription 'mysubscription' created in namespace 'default'.

Verification

• To confirm that a subscription connects the channel to the event sink, or subscriber, list the existing subscriptions and inspect the output by running the following command:

  $ kn subscription list

  You get an output similar to the following example:

  NAME            CHANNEL             SUBSCRIBER           REPLY   DEAD LETTER SINK   READY   REASON
  mysubscription   Channel:mychannel   ksvc:event-display                              True

Prerequisites

• You have installed the OpenShift Serverless Operator and Knative Eventing on your OpenShift Container Platform 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.
• The subscription that you want to delete exists.

Prerequisites

• You have installed the Knative (kn) CLI.
• You have created a subscription in your cluster.

Procedure

• Describe a subscription by running the following command:

  $ kn subscription describe <subscription_name>

  You get an output similar to the following example:

  Name:            my-subscription
  Namespace:       default
  Annotations:     messaging.knative.dev/creator=openshift-user, messaging.knative.dev/lastModifier=min ...
  Age:             43s
  Channel:         Channel:my-channel (messaging.knative.dev/v1)
  Subscriber:
    URI:           http://edisplay.default.example.com
  Reply:
    Name:          default
    Resource:      Broker (eventing.knative.dev/v1)
  DeadLetterSink:
    Name:          my-sink
    Resource:      Service (serving.knative.dev/v1)
  
  Conditions:
    OK TYPE                  AGE REASON
    ++ Ready                 43s
    ++ AddedToChannel        43s
    ++ ChannelReady          43s
    ++ ReferencesResolved    43s

Prerequisites

• You have installed the Knative (kn) CLI.

Procedure

• List subscriptions on your cluster by running the following command:

  $ kn subscription list

  You get an output similar to the following example:

  NAME             CHANNEL             SUBSCRIBER           REPLY   DEAD LETTER SINK   READY   REASON
  mysubscription   Channel:mychannel   ksvc:event-display                              True

Prerequisites

• You have installed the Knative (kn) CLI.
• You have created a subscription.

Procedure

• Update a subscription by running the following command: