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Event delivery - Develop | Serverless | OpenShift Container Platform 4.8
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Event delivery

You can configure event delivery parameters that are applied in cases where an event fails to be delivered to an event sink. Configuring event delivery parameters, including a dead letter sink, ensures that any events that fail to be delivered to an event sink are retried. Otherwise, undelivered events are dropped.

Event delivery behavior patterns for channels and brokers

Different channel and broker types have their own behavior patterns that are followed for event delivery.

Knative Kafka channels and brokers

If an event is successfully delivered to a Kafka channel or broker receiver, the receiver responds with a 202 status code, which means that the event has been safely stored inside a Kafka topic and is not lost.

If the receiver responds with any other status code, the event is not safely stored, and steps must be taken by the user to resolve the issue.

Configurable event delivery parameters

The following parameters can be configured for event delivery:

Dead letter sink

You can configure the deadLetterSink delivery parameter so that if an event fails to be delivered, it is stored in the specified event sink. Undelivered events that are not stored in a dead letter sink are dropped. The dead letter sink be any addressable object that conforms to the Knative Eventing sink contract, such as a Knative service, a Kubernetes service, or a URI.

Retries

You can set a minimum number of times that the delivery must be retried before the event is sent to the dead letter sink, by configuring the retry delivery parameter with an integer value.

Back off delay

You can set the backoffDelay delivery parameter to specify the time delay before an event delivery retry is attempted after a failure. The duration of the backoffDelay parameter is specified using the ISO 8601 format. For example, PT1S specifies a 1 second delay.

Back off policy

The backoffPolicy delivery parameter can be used to specify the retry back off policy. The policy can be specified as either linear or exponential. When using the linear back off policy, the back off delay is equal to backoffDelay * <numberOfRetries>. When using the exponential backoff policy, the back off delay is equal to backoffDelay*2^<numberOfRetries>.

Examples of configuring event delivery parameters

You can configure event delivery parameters for Broker, Trigger, Channel, and Subscription objects. If you configure event delivery parameters for a broker or channel, these parameters are propagated to triggers or subscriptions created for those objects. You can also set event delivery parameters for triggers or subscriptions to override the settings for the broker or channel.

Example Broker object
apiVersion: eventing.knative.dev/v1
kind: Broker
metadata:
...
spec:
  delivery:
    deadLetterSink:
      ref:
        apiVersion: eventing.knative.dev/v1alpha1
        kind: KafkaSink
        name: <sink_name>
    backoffDelay: <duration>
    backoffPolicy: <policy_type>
    retry: <integer>
...
Example Trigger object
apiVersion: eventing.knative.dev/v1
kind: Trigger
metadata:
...
spec:
  broker: <broker_name>
  delivery:
    deadLetterSink:
      ref:
        apiVersion: serving.knative.dev/v1
        kind: service
        name: <sink_name>
    backoffDelay: <duration>
    backoffPolicy: <policy_type>
    retry: <integer>
...
Example Channel object
apiVersion: messaging.knative.dev/v1
kind: Channel
metadata:
...
spec:
  delivery:
    deadLetterSink:
      ref:
        apiVersion: serving.knative.dev/v1
        kind: service
        name: <sink_name>
    backoffDelay: <duration>
    backoffPolicy: <policy_type>
    retry: <integer>
...
Example Subscription object
apiVersion: messaging.knative.dev/v1
kind: Subscription
metadata:
...
spec:
  channel:
    apiVersion: messaging.knative.dev/v1
    kind: Channel
    name: <channel_name>
  delivery:
    deadLetterSink:
      ref:
        apiVersion: serving.knative.dev/v1
        kind: service
        name: <sink_name>
    backoffDelay: <duration>
    backoffPolicy: <policy_type>
    retry: <integer>
...

Configuring event delivery ordering for triggers

If you are using a Kafka broker, you can configure the delivery order of events from triggers to event sinks.

Prerequisites

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

  • Kafka broker is enabled for use on your cluster, and you have created a Kafka broker.

  • 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.

  • You have installed the OpenShift (oc) CLI.

Procedure

  1. Create or modify a Trigger object and set the kafka.eventing.knative.dev/delivery.order annotation:

    apiVersion: eventing.knative.dev/v1
kind: Trigger
metadata:
  name: <trigger_name>
  annotations:
     kafka.eventing.knative.dev/delivery.order: ordered
...

    The supported consumer delivery guarantees are:

    unordered

    An unordered consumer is a non-blocking consumer that delivers messages unordered, while preserving proper offset management.

    ordered

    An ordered consumer is a per-partition blocking consumer that waits for a successful response from the CloudEvent subscriber before it delivers the next message of the partition.

    The default ordering guarantee is unordered.

  2. Apply the Trigger object:

    $ oc apply -f <filename>