Apache Kafka source example¶

Tutorial on how to build and deploy a KafkaSource event source.

Background¶

The KafkaSource reads all the messages, from all partitions, and sends those messages as CloudEvents through HTTP to its configured sink. The KafkaSource supports an ordered consumer delivery guaranty, which is a per-partition blocking consumer that waits for a successful response from the CloudEvent subscriber before it delivers the next message of the partition.

Note

If you need a more sophisticated Kafka Consumer, with direct access to specific partitions or offsets, you can implement a Kafka Consumer by using one of the available Apache Kafka SDKs.

Install the Kafka event source CRD¶

Set up a Kubernetes cluster with the Kafka event source installed. You can install the Kafka event source by using YAML or the Knative Operator.

Optional: Create a Kafka topic¶

If you are using Strimzi:

Create a KafkaTopic YAML file:

apiVersion: kafka.strimzi.io/v1beta2
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

Deploy the KafkaTopic YAML file by running the command:
```
kubectl apply -f <filename>.yaml
```
Where <filename> is the name of your KafkaTopic YAML file.

Example output:
```
kafkatopic.kafka.strimzi.io/knative-demo-topic created
```

Ensure that the KafkaTopic is running by running the command:

kubectl -n kafka get kafkatopics.kafka.strimzi.io

Example output:

NAME                 AGE
knative-demo-topic   16s

Create a Service¶

Clone the sample code GitHub repository, and navigate to the local directory of the repository:

git clone -b "main" https://github.com/knative/docs knative-docs

cd knative-docs/code-samples/eventing/kafka/source

2. Create the event-display Service as a YAML file:

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/tree/main/cmd/event_display/main.go
          image: gcr.io/knative-releases/knative.dev/eventing/cmd/event_display

Apply the YAML file by running the command:
```
kubectl apply -f <filename>.yaml
```
Where <filename> is the name of the file you created in the previous step.

Example output:
```
service.serving.knative.dev/event-display created
```

Ensure that the Service Pod is running, by running the command:

kubectl get pods

The Pod name is prefixed with event-display:

NAME                                            READY     STATUS    RESTARTS   AGE
event-display-00001-deployment-5d5df6c7-gv2j4   2/2       Running   0          72s

Kafka event source¶

Modify source/event-source.yaml accordingly with bootstrap servers, topics, and so on:

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

Deploy the event source:

kubectl apply -f event-source.yaml

Example output:

kafkasource.sources.knative.dev/kafka-source created

Verify that the event source Pod is running:

kubectl get pods

The Pod name is prefixed with kafka-source:

NAME                                  READY     STATUS    RESTARTS   AGE
kafka-source-xlnhq-5544766765-dnl5s   1/1       Running   0          40m

Ensure that the Kafka event source started with the necessary configuration:

kubectl logs --selector='knative-eventing-source-name=kafka-source'

Example output:

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

Verify¶

Produce a message ({"msg": "This is a test!"}) to the Apache Kafka topic as in the following example:

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

Tip

If you don't see a command prompt, try pressing Enter.

Verify that the Kafka event source consumed the message and sent it to its Sink properly. Because 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": ""
      }
    }

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

kubectl logs --selector='knative-eventing-source-name=kafka-source'

Example output:

{"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":"."}

Verify that the Service received the message from the event source:

kubectl logs --selector='serving.knative.dev/service=event-display' -c user-container

Example output:

☁️ 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!"
    }

Clean up steps¶

Delete the Kafka event source:

kubectl delete -f source/source.yaml kafkasource.sources.knative.dev

Example output:

"kafka-source" deleted

Delete the event-display Service:

kubectl delete -f source/event-display.yaml service.serving.knative.dev

Example output:

"event-display" deleted

Remove the Kafka event controller:

kubectl delete -f https://storage.googleapis.com/knative-releases/eventing-contrib/latest/kafka-source.yaml

Example output:

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

Optional: Remove the Apache Kafka Topic

kubectl delete -f kafka-topic.yaml

Example output:

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 the key deserializer, add the label kafkasources.sources.knative.dev/key-type to the KafkaSource definition, as shown in the following example:

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

Optional: Specify the initial offset¶

By default the KafkaSource starts consuming from the latest offset in each partition. If you want to consume from the earliest offset, set the initialOffset field to earliest, for example:

apiVersion: sources.knative.dev/v1beta1
kind: KafkaSource
metadata:
name: kafka-source
spec:
consumerGroup: knative-group
initialOffset: earliest
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

Note

The valid values for initialOffset are earliest and latest. Any other value results in a validation error. This field is honored only if there are no prior committed offsets for that consumer group.

Connecting to a TLS-enabled Kafka Broker¶

The KafkaSource supports TLS and SASL authentication methods. To enable TLS authentication, you must have the following files:

CA Certificate
Client Certificate and Key

KafkaSource expects these files to be in PEM format. If they are in another format, such as JKS, convert them to PEM.

Create the certificate files as secrets in the namespace where KafkaSource is going to be set up, by running the commands:

kubectl create secret generic cacert --from-file=caroot.pem

kubectl create secret tls kafka-secret --cert=certificate.pem --key=key.pem

Apply the KafkaSource. Modify the bootstrapServers and topics fields 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