Apache Kafka Source Example

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

Prerequisites

• Ensure that you meet the prerequisites listed in the Apache Kafka overview.
• A Kubernetes cluster with Knative Kafka Source installed.

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

```

1. 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