Chapter 7. Subscriptions

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.
• You have created a Knative channel.
• You have created a Knative service to use as a subscriber.

Prerequisites

• The OpenShift Serverless Operator, Knative Serving, and Knative Eventing are installed 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 permissions to create applications and other workloads in OpenShift Container Platform.

Verification

• After the subscription has been created, you can see it represented as a line that connects the channel to the service in the Topology view:

  

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

• Create a Subscription object:

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

    apiVersion: messaging.knative.dev/v1beta1
    kind: Subscription
    metadata:
      name: my-subscription 1
      namespace: default
    spec:
      channel: 2
        apiVersion: messaging.knative.dev/v1beta1
        kind: Channel
        name: example-channel
      delivery: 3
        deadLetterSink:
          ref:
            apiVersion: serving.knative.dev/v1
            kind: Service
            name: error-handler
      subscriber: 4
        ref:
          apiVersion: serving.knative.dev/v1
          kind: Service
          name: event-display

    1

    Name of the subscription.

    2

    Configuration settings for the channel that the subscription connects to.

    3

    Configuration settings for event delivery. This tells the subscription what happens to events that cannot be delivered to the subscriber. When this is configured, events that failed to be consumed are sent to the deadLetterSink. The event is dropped, no re-delivery of the event is attempted, and an error is logged in the system. The deadLetterSink value must be a Destination.

    4

    Configuration settings for the subscriber. This is the event sink that events are delivered to from the channel.

  • Apply the YAML file:

    $ oc apply -f <filename>

Prerequisites

• The OpenShift Serverless Operator and Knative Eventing are installed 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> \ 1
    --sink <sink_prefix>:<sink_name> \ 2
    --sink-dead-letter <sink_prefix>:<sink_name> 3

  1

  --channel specifies the source for cloud events that should be processed. You must provide the channel name. If you are not using the default InMemoryChannel channel that is backed by the Channel custom resource, you must prefix the channel name with the <group:version:kind> for the specified channel type. For example, this will be messaging.knative.dev:v1beta1:KafkaChannel for an Apache Kafka backed channel.

  2

  --sink specifies the target destination to which the event should be delivered. By default, the <sink_name> is interpreted as a Knative service of this name, in the same namespace as the subscription. You can specify the type of the sink by using one of the following prefixes:

  ksvc

  A Knative service.

  channel

  A channel that should be used as destination. Only default channel types can be referenced here.

  broker

  An Eventing broker.

  3

  Optional: --sink-dead-letter is an optional flag that can be used to specify a sink which events should be sent to in cases where events fail to be delivered. For more information, see the OpenShift Serverless Event delivery documentation.

  Example command

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

  Example output

  Subscription 'mysubscription' created in namespace 'default'.

Verification

• To confirm that the channel is connected to the event sink, or subscriber, by a subscription, list the existing subscriptions and inspect the output:

  $ kn subscription list

  Example output

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

Deleting a subscription

• Delete a subscription:

  $ kn subscription delete <subscription_name>

• Configure event delivery parameters that are applied in cases where an event fails to be delivered to an event sink.

Prerequisites

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

Procedure

• Describe a subscription:

  $ kn subscription describe <subscription_name>

  Example output

  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:

  $ kn subscription list

  Example output

  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:

  $ kn subscription update <subscription_name> \
    --sink <sink_prefix>:<sink_name> \ 1
    --sink-dead-letter <sink_prefix>:<sink_name> 2

  1

  --sink specifies the updated target destination to which the event should be delivered. You can specify the type of the sink by using one of the following prefixes:

  ksvc

  A Knative service.

  channel

  A channel that should be used as destination. Only default channel types can be referenced here.

  broker

  An Eventing broker.

  2

  Optional: --sink-dead-letter is an optional flag that can be used to specify a sink which events should be sent to in cases where events fail to be delivered. For more information, see the OpenShift Serverless Event delivery documentation.

  Example command

  $ kn subscription update mysubscription --sink ksvc:event-display