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Dead Letter Sink and Retries pattern

Dead letter sink are Event sinks that receive events that can't be processed successfully by subscribers.

Dead letter sinks are useful for debugging applications because they let you isolate unconsumed events to determine why their processing didn't succeed.

Example

  1. Run the following command to create the resources to showcase dead letter sinks and retries: 
    $ kubectl apply -f example.yaml
  2. View logs: 
    $ kubectl logs -l=app=event-display -f

☁️  cloudevents.Event
  Context Attributes,
  specversion: 1.0
  type: dev.knative.sources.ping
  source: /apis/v1/namespaces/default/pingsources/with-dead-letter-sink
  id: f95a3409-12dc-4ed2-ba53-dbd60210e036
  time: 2024-02-15T14:26:00.115167526Z
  Extensions,
  knativearrivaltime: 2024-02-15T14:26:00.11706994Z
  knativebrokerttl: 255
  knativeerrorcode: 500
  knativeerrordata: ZGlzcGF0Y2ggZXJyb3I6IFBvc3QgImh0dHA6Ly9mYWlsLmRlZmF1bHQuc3ZjLmNsdXN0ZXIubG9jYWwiOiBkaWFsIHRjcDogbG9va3VwIGZhaWwuZGVmYXVsdC5zdmMuY2x1c3Rlci5sb2NhbCBvbiAxMC45Ni4wLjEwOjUzOiBubyBzdWNoIGhvc3Q=
  knativeerrordest: http://fail.default.svc.cluster.local
  Data,
  Hello World!
    Example output: 
    

    3. 

  3. Debugging the reason using knativeerrordata attribute:

    $ echo ZGlzcGF0Y2ggZXJyb3I6IFBvc3QgImh0dHA6Ly9mYWlsLmRlZmF1bHQuc3ZjLmNsdXN0ZXIubG9jYWwiOiBkaWFsIHRjcDogbG9va3VwIGZhaWwuZGVmYXVsdC5zdmMuY2x1c3Rlci5sb2NhbCBvbiAxMC45Ni4wLjEwOjUzOiBubyBzdWNoIGhvc3Q= | base64 -d
dispatch error: Post "http://fail.default.svc.cluster.local": dial tcp: lookup fail.default.svc.cluster.local on 10.96.0.10:53: no such host
    

    4.