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 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. Download a copy of the code:

    git clone -b "release-0.14" https://github.com/knative/docs knative-docs
cd knative-docs/docs/eventing/samples/kafka/source

  2. Build the Event Display Service (event-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/knative.dev/eventing-contrib/cmd/event_display

  3. Deploy the Event Display Service

    $ kubectl apply --filename event-display.yaml
...
service.serving.knative.dev/event-display created

  4. 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 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-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