Event delivery

You can configure event delivery parameters for Knative Eventing components that are applied in cases where an event fails to be delivered

Configuring subscription event delivery

You can configure how events are delivered for each subscription by adding a delivery spec to the Subscription object, as shown in the following example:

apiVersion: messaging.knative.dev/v1
kind: Subscription
metadata:
  name: example-subscription
  namespace: example-namespace
spec:
  delivery:
    deadLetterSink:
      ref:
        apiVersion: serving.knative.dev/v1
        kind: Service
        name: example-sink
    backoffDelay: <duration>
    backoffPolicy: <policy-type>
    retry: <integer>

Where

  • The deadLetterSink spec contains configuration settings to enable using a dead letter sink. This tells the subscription what happens to events that cannot be delivered to the subscriber. When this is configured, events that fail to be delivered are sent to the dead letter sink destination. The destination can be a Knative service or a URI. In the example, the destination is a Service object, or Knative service, named example-sink.
  • The backoffDelay delivery parameter specifies 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.
  • 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 the time interval specified between retries. When using the exponential back off policy, the back off delay is equal to backoffDelay*2^<numberOfRetries>.
  • retry specifies the number of times that event delivery is retried before the event is sent to the dead letter sink.

Broker event delivery

See the broker documentation.

Channel event delivery

Failed events may, depending on the specific Channel implementation in use, be enhanced with extension attributes prior to forwarding to thedeadLetterSink. These extension attributes are as follows:

  • knativeerrorcode

    • Type: Int
    • Description: The HTTP Response StatusCode from the final event dispatch attempt.
    • Constraints: Should always be present as every HTTP Response contains a StatusCode.
    • Examples:
      • “500”
      • …any HTTP StatusCode…

  • knativeerrordata

    • Type: String
    • Description: The HTTP Response Body from the final event dispatch attempt.
    • Constraints: Will be empty if the HTTP Response Body was empty, and might be truncated if the length is excessive.
    • Examples:
      • ‘Internal Server Error: Failed to process event.’
      • ‘{“key”: “value”}’
      • …any HTTP Response Body…

Channel Support

The table below summarizes what delivery parameters are supported for each channel implementation.

Channel Type Supported Delivery Parameters
GCP PubSub none
In-Memory deadLetterSink, retry, backoffPolicy, backoffDelay
Kafka deadLetterSink, retry, backoffPolicy, backoffDelay
Natss none