Apache Kafka Source Example

Tutorial on how to build and deploy a KafkaSource Eventing source using a Knative Serving Service.

Prerequisites

You must ensure that you meet the prerequisites listed in the Apache Kafka overview.

Creating a KafkaSource source CRD

  1. Install the KafkaSource sub-component to your Knative cluster:
    kubectl apply -f https://storage.googleapis.com/knative-releases/eventing-contrib/latest/kafka-source.yaml
    
    
  2. Check that the kafka-controller-manager-0 pod is running.
    kubectl get pods --namespace knative-sources
    NAME                         READY     STATUS    RESTARTS   AGE
    kafka-controller-manager-0   1/1       Running   0          42m
    
  3. Check the kafka-controller-manager-0 pod logs.
    $ kubectl logs kafka-controller-manager-0 -n knative-sources
    2019/03/19 22:25:54 Registering Components.
    2019/03/19 22:25:54 Setting up Controller.
    2019/03/19 22:25:54 Adding the Apache Kafka Source controller.
    2019/03/19 22:25:54 Starting Apache Kafka controller.
    

Apache Kafka Topic (Optional)

  1. If using Strimzi, you can set a topic modifying source/kafka-topic.yaml with your desired:
  • Topic

  • Cluster Name

  • Partitions

  • Replicas

    apiVersion: kafka.strimzi.io/v1beta1
    kind: KafkaTopic
    metadata:
      name: knative-demo-topic
      namespace: kafka
      labels:
        strimzi.io/cluster: my-cluster
    spec:
      partitions: 3
      replicas: 1
      config:
        retention.ms: 7200000
        segment.bytes: 1073741824
    
  1. Deploy the KafkaTopic

    $ kubectl apply -f kafka/source/samples/strimzi-topic.yaml
    kafkatopic.kafka.strimzi.io/knative-demo-topic created
    
  2. Ensure the KafkaTopic is running.

    $ kubectl -n kafka get kafkatopics.kafka.strimzi.io
    NAME                 AGE
    knative-demo-topic   16s
    

Create the Event Display service

  1. Build the Event Display Service (even-display.yaml)

    apiVersion: serving.knative.dev/v1
    kind: Service
    metadata:
      name: event-display
      namespace: default
    spec:
      template:
        spec:
          containers:
            - # This corresponds to
              # https://github.com/knative/eventing-contrib/tree/master/cmd/event_display/main.go
              image: gcr.io/knative-releases/github.com/knative/eventing-contrib/cmd/event_display
    
  2. Deploy the Event Display Service

    $ kubectl apply --filename source/samples/event-display.yaml
    ...
    service.serving.knative.dev/event-display created
    
  3. Ensure that the Service pod is running. The pod name will be prefixed with event-display.

    $ kubectl get pods
    NAME                                            READY     STATUS    RESTARTS   AGE
    event-display-00001-deployment-5d5df6c7-gv2j4   2/2       Running   0          72s
    ...
    

Apache Kafka Event Source

  1. Modify source/event-source.yaml accordingly with bootstrap servers, topics, etc…:

    apiVersion: sources.eventing.knative.dev/v1alpha1
    kind: KafkaSource
    metadata:
      name: kafka-source
    spec:
      consumerGroup: knative-group
      bootstrapServers: my-cluster-kafka-bootstrap.kafka:9092 #note the kafka namespace
      topics: knative-demo-topic
      sink:
        ref:
          apiVersion: serving.knative.dev/v1
          kind: Service
          name: event-display
    
  2. Deploy the event source.

    $ kubectl apply -f kafka/source/samples/event-source.yaml
    ...
    kafkasource.sources.eventing.knative.dev/kafka-source created
    
  3. Check that the event source pod is running. The pod name will be prefixed with kafka-source.

    $ kubectl get pods
    NAME                                  READY     STATUS    RESTARTS   AGE
    kafka-source-xlnhq-5544766765-dnl5s   1/1       Running   0          40m
    
  4. Ensure the Apache Kafka Event Source started with the necessary configuration.

    $ kubectl logs --selector='knative-eventing-source-name=kafka-source'
    {"level":"info","ts":"2019-04-01T19:09:32.164Z","caller":"receive_adapter/main.go:97","msg":"Starting Apache Kafka Receive Adapter...","Bootstrap Server":"...","Topics":".","ConsumerGroup":"...","SinkURI":"...","TLS":false}
    

Verify

  1. Produce a message ({"msg": "This is a test!"}) to the Apache Kafka topic, like shown below:

    kubectl -n kafka run kafka-producer -ti --image=strimzi/kafka:0.14.0-kafka-2.3.0 --rm=true --restart=Never -- bin/kafka-console-producer.sh --broker-list my-cluster-kafka-bootstrap:9092 --topic knative-demo-topic
    If you don't see a command prompt, try pressing enter.
    >{"msg": "This is a test!"}
    
  2. Check that the Apache Kafka Event Source consumed the message and sent it to its sink properly.

    $ kubectl logs --selector='knative-eventing-source-name=kafka-source'
    ...
    {"level":"info","ts":"2019-04-15T20:37:24.702Z","caller":"receive_adapter/main.go:99","msg":"Starting Apache Kafka Receive Adapter...","bootstrap_server":"...","Topics":"knative-demo-topic","ConsumerGroup":"knative-group","SinkURI":"...","TLS":false}
    {"level":"info","ts":"2019-04-15T20:37:24.702Z","caller":"adapter/adapter.go:100","msg":"Starting with config: ","bootstrap_server":"...","Topics":"knative-demo-topic","ConsumerGroup":"knative-group","SinkURI":"...","TLS":false}
    {"level":"info","ts":1553034726.546107,"caller":"adapter/adapter.go:154","msg":"Successfully sent event to sink"}
    
  3. Ensure the Event Display received the message sent to it by the Event Source.

    $ kubectl logs --selector='serving.knative.dev/service=event-display' -c user-container
    
    

☁️ cloudevents.Event Validation: valid Context Attributes, specversion: 1.0 type: dev.knative.kafka.event source: /apis/v1/namespaces/default/kafkasources/kafka-source#my-topic subject: partition:0#564 id: partition:0/offset:564 time: 2020-02-10T18:10:23.861866615Z datacontenttype: application/json Extensions, key: Data, { “msg”: “This is a test!” }


## Teardown Steps

1. Remove the Apache Kafka Event Source

$ kubectl delete -f source/source.yaml kafkasource.sources.eventing.knative.dev “kafka-source” deleted

2. Remove the Event Display

$ kubectl delete -f source/event-display.yaml service.serving.knative.dev “event-display” deleted

3. Remove the Apache Kafka Event Controller

$ kubectl delete -f https://storage.googleapis.com/knative-releases/eventing-contrib/latest/kafka-source.yaml serviceaccount “kafka-controller-manager” deleted clusterrole.rbac.authorization.k8s.io “eventing-sources-kafka-controller” deleted clusterrolebinding.rbac.authorization.k8s.io “eventing-sources-kafka-controller” deleted customresourcedefinition.apiextensions.k8s.io “kafkasources.sources.eventing.knative.dev” deleted service “kafka-controller” deleted statefulset.apps “kafka-controller-manager” deleted

4. (Optional) Remove the Apache Kafka Topic

```shell
$ kubectl delete -f kafka/source/samples/kafka-topic.yaml
kafkatopic.kafka.strimzi.io "knative-demo-topic" deleted

(Optional) Specify the key deserializer

When KafkaSource receives a message from Kafka, it dumps the key in the Event extension called Key and dumps Kafka message headers in the extensions starting with kafkaheader.

You can specify the key deserializer among four types:

  • string (default) for UTF-8 encoded strings
  • int for 32-bit & 64-bit signed integers
  • float for 32-bit & 64-bit floating points
  • byte-array for a Base64 encoded byte array

To specify it, add the label kafkasources.sources.eventing.knative.dev/key-type to the KafkaSource definition like:

apiVersion: sources.eventing.knative.dev/v1alpha1
kind: KafkaSource
metadata:
 name: kafka-source
 labels:
  kafkasources.sources.eventing.knative.dev/key-type: int
spec:
 consumerGroup: knative-group
 bootstrapServers: my-cluster-kafka-bootstrap.kafka:9092 #note the kafka namespace
 topics: knative-demo-topic
 sink:
   ref:
     apiVersion: serving.knative.dev/v1
     kind: Service
     name: event-display