Apache Kafka Binding Example

KafkaBinding is responsible for injecting Kafka bootstrap connection information into a Kubernetes resource that embed a PodSpec (as spec.template.spec). This enables easy bootstrapping of a Kafka client.

Create a Job that uses KafkaBinding

In the below 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

Prerequisites

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:

   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

Create the Event Display service

1. (Optional) Source code for Event Display service

   Get the source code of Event Display container image from here

2. 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-contrib/cmd/event_display

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

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

   Alternatively, you can create the knative service using the kn cli like below

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

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 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
     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.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

Kafka Binding Resource

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

   Get the source code of kafka-publisher container image from here

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

   apiVersion: batch/v1
   kind: Job
   metadata:
     labels:
       kafka.topic: "logs"
     name: kafka-publisher-job
   spec:
     backoffLimit: 1
     completions: 1
     parallelism: 1
     template:
       metadata:
         annotations:
           sidecar.istio.io/inject: "false"
       spec:
         restartPolicy: Never
         containers:
           - image: docker.io/murugappans/kafka-publisher-1974f83e2ff7c8994707b5e8731528e8@sha256:fd79490514053c643617dc72a43097251fed139c966fd5d131134a0e424882de
             env:
               - name: KAFKA_TOPIC
                 value: "logs"
               - name: KAFKA_KEY
                 value: "0"
               - name: KAFKA_HEADERS
                 value: "content-type:application/json"
               - name: KAFKA_VALUE
                 value: '{"msg":"This is a test!"}'
             name: kafka-publisher

3. Check that the Job has run successfully.

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

Verify

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
   Extensions,
     kafkaheadercontenttype: application/json
     key: 0
     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, please have the below 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

2. 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:
    - my-secure-kafka-bootstrap.kafka:443

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