Apache Kafka Source Example

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

Prerequisites

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 "{{< branch >}}" 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.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:
      - 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.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":"2020-05-28T10:39:42.104Z","caller":"adapter/adapter.go:81","msg":"Starting with config: ","Topics":".","ConsumerGroup":"...","SinkURI":"...","Name":".","Namespace":"."}
    

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. Since these logs are captured in debug level, edit the key level of config-logging configmap in knative-sources namespace to look like this:

    data:
      loglevel.controller: info
      loglevel.webhook: info
      zap-logger-config: |
        {
          "level": "debug",
          "development": false,
          "outputPaths": ["stdout"],
          "errorOutputPaths": ["stderr"],
          "encoding": "json",
          "encoderConfig": {
            "timeKey": "ts",
            "levelKey": "level",
            "nameKey": "logger",
            "callerKey": "caller",
            "messageKey": "msg",
            "stacktraceKey": "stacktrace",
            "lineEnding": "",
            "levelEncoder": "",
            "timeEncoder": "iso8601",
            "durationEncoder": "",
            "callerEncoder": ""
          }
        }
    
    

    Now manually delete the kafkasource deployment and allow the kafka-controller-manager deployment running in knative-sources namespace to redeploy it. Debug level logs should be visible now.

    $ kubectl logs --selector='knative-eventing-source-name=kafka-source'
    ...
    
    {"level":"debug","ts":"2020-05-28T10:40:29.400Z","caller":"kafka/consumer_handler.go:77","msg":"Message claimed","topic":".","value":"."}
    {"level":"debug","ts":"2020-05-28T10:40:31.722Z","caller":"kafka/consumer_handler.go:89","msg":"Message marked","topic":".","value":"."}
    
  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.knative.dev
    "kafka-source" deleted
    
    
    1. Remove the Event Display
    
    \$ kubectl delete -f source/event-display.yaml service.serving.knative.dev
    "event-display" deleted
    
    
    1. 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.knative.dev"
    deleted service "kafka-controller" deleted statefulset.apps
    "kafka-controller-manager" deleted
    
    
  2. (Optional) Remove the Apache Kafka Topic

    $ 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.knative.dev/key-type to the KafkaSource definition like:

apiVersion: sources.knative.dev/v1beta1
kind: KafkaSource
metadata:
 name: kafka-source
 labels:
   kafkasources.sources.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

Connecting to a TLS enabled Kafka broker

The KafkaSource supports TLS and SASL authentication methods. For enabling TLS authentication, please have the below files

  • CA Certificate
  • Client Certificate and Key

KafkaSource expects these files 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 KafkaSource 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 KafkaSource, change bootstrapServers and topics accordingly.

    apiVersion: sources.knative.dev/v1beta1
    kind: KafkaSource
    metadata:
     name: kafka-source-with-tls
    spec:
     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
    topics:
    - knative-demo-topic
    sink:
      ref:
        apiVersion: serving.knative.dev/v1
        kind: Service
        name: event-display