Apache Kafka Binding Example

In the following example a Kubernetes Job will be using the KafkaBinding to produce messages on a Kafka Topic, which will be received by the Event Display service via Kafka Source

1. You must ensure that you meet the prerequisites listed in the Apache Kafka overview.
2. This feature is available from Knative Eventing 0.15+

Creating a KafkaSource source CRD

1. Install the KafkaSource sub-component to your Knative cluster:

1. 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

1. (Optional) Source code for Event Display service

Get the source code of Event Display container image from here

1. Deploy the Event Display Service via kubectl:

apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: event-display
spec:
  template:
    spec:
      containers:
        - image: gcr.io/knative-releases/knative.dev/eventing/cmd/event_display

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

1. (Optional) Deploy the Event Display Service via kn cli:

Alternatively, you can create the knative service by running the following command in the kn CLI.

kn service create event-display --image=gcr.io/knative-releases/knative.dev/eventing/cmd/event_display

Apache Kafka Event Source

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

apiVersion: sources.knative.dev/v1beta1
kind: KafkaSource
metadata:
  name: kafka-source
spec:
  consumerGroup: knative-group
  bootstrapServers:
    - my-cluster-kafka-bootstrap.kafka:9092 #note the kafka namespace
  topics:
    - logs
    ref:
      apiVersion: serving.knative.dev/v1
      kind: Service
      name: event-display

1. Deploy the event source.

   $ kubectl apply -f event-source.yaml
   kafkasource.sources.knative.dev/kafka-source created

2. 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

Create the KafkaBinding that will inject kafka bootstrap information into select Jobs:

1. Modify kafka-binding.yaml accordingly with bootstrap servers etc…:

apiVersion: bindings.knative.dev/v1beta1
kind: KafkaBinding
metadata:
  name: kafka-binding-test
spec:
  subject:
    apiVersion: batch/v1
    kind: Job
    selector:
      matchLabels:
        kafka.topic: "logs"
  bootstrapServers:
    - my-cluster-kafka-bootstrap.kafka:9092

In this case, we will bind any Job with the labels kafka.topic: "logs".

Create Kubernetes Job

1. Source code for kafka-publisher service

1. Now we will use the kafka-publisher container to send events to kafka topic when the Job runs.

1. Check that the Job has run successfully.

$ kubectl get jobs
NAME                  COMPLETIONS   DURATION   AGE
kafka-publisher-job   1/1          7s         7s

1. 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#logs
  subject: partition:0#1
  id: partition:0/offset:1
  time: 2020-05-17T19:45:02.7Z
  datacontenttype: application/json
  kafkaheadercontenttype: application/json
  traceparent: 00-f383b779f512358b24ffbf6556a6d6da-cacdbe78ef9b5ad3-00
Data,
  {
    "msg": "This is a test!"
  }

Connecting to a TLS enabled Kafka broker

The KafkaBinding supports TLS and SASL authentication methods. For injecting TLS authentication, you must have the following files:

• CA Certificate
• Client Certificate and Key

These files are expected to be in pem format, if it is in other format like jks , please convert to pem.

1. Create the certificate files as secrets in the namespace where KafkaBinding is going to be set up

$ kubectl create secret generic cacert --from-file=caroot.pem
secret/cacert created
$ kubectl create secret tls kafka-secret --cert=certificate.pem --key=key.pem
secret/key created

1. Apply the kafkabinding-tls.yaml, change bootstrapServers accordingly.

   apiVersion: sources.knative.dev/v1beta1
   kind: KafkaBinding
   metadata:
    name: kafka-source-with-tls
   spec:
    subject:
      apiVersion: batch/v1
       kind: Job
       selector:
         matchLabels:
           kafka.topic: "logs"
    net:
      tls:
        enable: true
        cert:
          secretKeyRef:
            key: tls.crt
            name: kafka-secret
        key:
          secretKeyRef:
            key: tls.key
            name: kafka-secret
        caCert:
          secretKeyRef:
            key: caroot.pem
            name: cacert
    consumerGroup: knative-group
    bootstrapServers: