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Ashok Nagaraj
Ashok Nagaraj

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Knative eventing workflow example

What we want to implement

Inteded workflow

What we have (pre-requisite)

  1. A kubernetes cluster (kind cluster in my case => no external urls possible)
  2. Knative serving installed (installation script)
  3. Knative eventing installed (installation script)
  4. Kafka related broker, source, sink .. (installation script)
  5. A kafka cluster (internal cluster installation script) - broker url will be http://my-cluster.kafka-ns.cluster.local:9092. Note: I am using a cluster hosted on in my examples (installation link)
  6. Microservices invoked via POST: 6a. Builder-MS - external (emits CE with "[BUILD] ") 6b. Tester-MS - internal (sequence: emits CE with "..Create TB..", "Run Tests", "..Clean TB..") 6c. Committer-MS - external (emits CE with "[COMMIT]") 6d. Alerter-MS - internal (records and displays the events - for demo; can be event-display service with kn service create alert-ms

Intended workflow

  1. GitHubSource - is registered with GitHub which pushes events (PR related) to GitHubSource (installation)
    Note: Since I am working on localhost/kind, I will skip this part
    1a. Every EventSource needs a Sink; in this case we use http://Builder-MS-URL as the Sink
    Note: I will directly invoke this http://Builder-MS-URL via POST

  2. Builder MS - Microservice that builds and posts a build.done{} with a Ce-buildstatus=xyz event to Kafka topic build.done

  3. KafkaSource - Subscribes to topic build.done and passes it on-to Sink=Broker:kb-build
    3a. Broker kb-build passes on the event to trigger:kt-build

  4. Trigger(kt-build) - if buildstatus=pass pass the event to Sink:sequence, if buildstatus=fail pass it to http://Alerter-MS-URL

  5. Sequence - calls 3 services create-tb-ms, run-tests-ms, clean-tb-ms and passes the results on-to Sink=Broker:kb-test

  6. Broker(kb-test)/Trigger(kt-test) - if teststatus=pass pass the event to Sink:KafkaSink, if teststatus=fail pass it to http://Alerter-MS-URL

  7. KafkaSink - posts test.done{} with teststatus=pass to kafka topic: test.done

  8. KafkaSource - Subscribes to topic test.done and passes it on-to Sink=http://Commit-MS-URL

  9. Commit MS - Does commit process and posts a Cloud-event


  1. All the manifests are under github directory
  2. The demo uses InMemory Channel for the brokers when created with, use for Kafka based broker implementation
  3. Steps #6, #7 and #8 can be avoided by directly calling Commit MS; I use it to add teststatus with CeOverrides which is only available through an EventSource
  4. Use SinkBinding if you directly want to call an EventSink
  5. Tester MS is always returning teststatus=pass in my case as it is a dummy sequence
  6. Kafka brokers and triggers need to be in the same namespace to work properly

Test run

# post installation, these are the knative objects
❯ kn sources list -A
NAMESPACE   NAME            TYPE          RESOURCE                           SINK               READY
kafka-ns    ks-build-done   KafkaSource   broker:kb-test     True
kafka-ns    ks-test-done    KafkaSource   broker:kb-commit   True

❯ kn service list -A
NAMESPACE   NAME           URL                                             LATEST               AGE   CONDITIONS   READY   REASON
default     alert-ms       http://alert-ms.default.svc.cluster.local       alert-ms-00001       17h   3 OK / 3     True
default     clean-tb-ms    http://clean-tb-ms.default.svc.cluster.local    clean-tb-ms-00001    17h   3 OK / 3     True
default     create-tb-ms   http://create-tb-ms.default.svc.cluster.local   create-tb-ms-00001   17h   3 OK / 3     True
default     run-tests-ms   http://run-tests-ms.default.svc.cluster.local   run-tests-ms-00001   17h   3 OK / 3     True

❯ kubectl get
NAME      URL                                                                 AGE   READY   REASON
test-ms   http://test-ms-kn-sequence-0-kn-channel.default.svc.cluster.local   17h   True

❯ kn broker list -A
NAMESPACE   NAME        URL                                                                           AGE   CONDITIONS   READY   REASON
kafka-ns    kb-build    http://broker-ingress.knative-eventing.svc.cluster.local/kafka-ns/kb-build    17h   6 OK / 6     True
kafka-ns    kb-commit   http://broker-ingress.knative-eventing.svc.cluster.local/kafka-ns/kb-commit   17h   6 OK / 6     True
kafka-ns    kb-test     http://broker-ingress.knative-eventing.svc.cluster.local/kafka-ns/kb-test     17h   6 OK / 6     True

❯ kn trigger list -A
NAMESPACE   NAME              BROKER      SINK                                                        AGE   CONDITIONS   READY   REASON
kafka-ns    kt-build-start    kb-build    http://builer-ms-url                         17h   6 OK / 6     True
kafka-ns    kt-commit-start   kb-commit   http://commiter-ms-url                        17h   6 OK / 6     True
kafka-ns    kt-test-start     kb-test     sequence:test-ms                                            17h   6 OK / 6     True

# trigger the workflow by calling `builder-ms-url`
❯ http POST http://builer-ms-url ...
HTTP/1.0 200 OK
Content-Length: 263
Date: Wed, 29 Mar 2023 08:36:44 GMT
Server: Werkzeug/2.0.3 Python/3.6.3
content-type: application/cloudevents+json

    "buildstatus": "pass",
    "data": {
        "message": "[BUILD] BUGmn15840",
        "completed": true
    "id": "6110dd6e-f670-4ede-a41b-3f671219ae0d",
    "source": "",
    "specversion": "1.0",
    "task": "build",
    "time": "2023-03-29T08:36:37.353013+00:00",
    "type": "build.pass"

## output events in the order of arrival
# 1. output from build
# ce-source: /apis/v1/namespaces/kafka-ns/kafkasources/ks-build-done#build.pass
# ce-buildstatus: pass
# ce-type: dev.knative.kafka.event
  "message": "[BUILD] BUGmn15840",
  "completed": true

#2. output from test
# ce-source: /apis/v1/namespaces/kafka-ns/kafkasources/ks-build-done#build.pass
# ce-buildstatus: pass
# ce-teststatus: pass
# ce-type: dev.knative.kafka.event
  "id": 1234,
  "message": "[BUILD] BUGmn15840...Create TB......Run tests......Clean TB..."
  "completed": true

#3. output from commit
# ce-source: demo.commit
# ce-buildstatus: pass
# ce-teststatus: pass
# ce-commitstatus: pass
# ce-type: commit.pass
  "message": "[BUILD] BUGmn15840...Create TB......Run tests......Clean TB... [COMMIT] ",
  "completed": true
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