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Chapter 8. Event delivery
You can configure event delivery parameters that are applied in cases where an event fails to be delivered to an event sink. Different channel and broker types have their own behavior patterns that are followed for event delivery.
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.
If an event is successfully delivered to a channel or broker receiver for Apache Kafka, 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.
8.1. Configurable event delivery parameters
You can configure the following parameters for event delivery:
- Dead letter sink
-
You can configure the
deadLetterSinkdelivery parameter to store events that fail delivery in the specified event sink. The system drops undelivered events that are not stored in a dead letter sink. The dead letter sink can 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 configure the retry delivery parameter with an integer value to set the minimum number of delivery attempts before the system sends the event to the dead letter sink.
- Back off delay
-
You can set the
backoffDelaydelivery parameter to specify the delay before the system retries event delivery after a failure. Specify thebackoffDelayvalue by using the ISO 8601 duration format. For example,PT1Sspecifies a delay of1second. - Back off policy
-
You can use the
backoffPolicydelivery parameter to specify the retry backoff policy. Specify the policy as eitherlinearorexponential. With thelinearpolicy, the system calculates the backoff delay asbackoffDelay * <numberOfRetries>. With theexponentialpolicy, the system calculates the backoff delay asbackoffDelay * 2^<numberOfRetries>.
8.2. 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 propagates 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>
# ...
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