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/github.com/knative/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/github.com/knative/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/v1alpha1
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/v1alpha1
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
  namespace: test-alpha
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

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/v1alpha1
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