Knative Sink for Apache Kafka

The KafkaSink is an Apache Kafka-native Sink implementation persisting the incoming CloudEvent to a configurable Apache Kafka Topic. This page shows how to install and configure the Knative KafkaSink.

Prerequisites

You must have access to a Kubernetes cluster with Knative Eventing installed.

Installation

1. Install the Kafka controller:

   kubectl apply -f https://storage.googleapis.com/knative-nightly/eventing-kafka-broker/latest/eventing-kafka-controller.yaml
   

2. Install the KafkaSink data plane:

   kubectl apply -f https://storage.googleapis.com/knative-nightly/eventing-kafka-broker/latest/eventing-kafka-sink.yaml
   

3. Verify that kafka-controller and kafka-sink-receiver Deployments are running:

   kubectl get deployments.apps -n knative-eventing
   

   Example output:

   NAME                           READY   UP-TO-DATE   AVAILABLE   AGE
   eventing-controller            1/1     1            1           10s
   eventing-webhook               1/1     1            1           9s
   kafka-controller               1/1     1            1           3s
   kafka-sink-receiver            1/1     1            1           5s
   

KafkaSink example

A KafkaSink object looks similar to the following:

apiVersion: eventing.knative.dev/v1alpha1
kind: KafkaSink
metadata:
  name: my-kafka-sink
  namespace: default
spec:
  topic: mytopic
  bootstrapServers:
   - my-cluster-kafka-bootstrap.kafka:9092

Output Topic Content Mode

The CloudEvent specification defines 2 modes to transport a CloudEvent: structured and binary.

A "structured-mode message" is one where the event is fully encoded using a stand-alone event format and stored in the message body.

The structured content mode keeps event metadata and data together in the payload, allowing simple forwarding of the same event across multiple routing hops, and across multiple protocols.

A "binary-mode message" is one where the event data is stored in the message body, and event attributes are stored as part of message meta-data.

The binary content mode accommodates any shape of event data, and allows for efficient transfer and without transcoding effort.

A KafkaSink object with a specified contentMode looks similar to the following:

apiVersion: eventing.knative.dev/v1alpha1
kind: KafkaSink
metadata:
  name: my-kafka-sink
  namespace: default
spec:
  topic: mytopic
  bootstrapServers:
   - my-cluster-kafka-bootstrap.kafka:9092

  # CloudEvent content mode of Kafka messages sent to the topic.
  # Possible values:
  # - structured
  # - binary
  #
  # default: binary.
  #
  # CloudEvent spec references:
  # - https://github.com/cloudevents/spec/blob/v1.0.2/cloudevents/spec.md#message
  # - https://github.com/cloudevents/spec/blob/v1.0.2/cloudevents/bindings/kafka-protocol-binding.md#33-structured-content-mode
  # - https://github.com/cloudevents/spec/blob/v1.0.2/cloudevents/bindings/kafka-protocol-binding.md#32-binary-content-mode
  contentMode: binary # or structured

Security

Knative supports the following Apache Kafka security features:

• Authentication using SASL without encryption
• Authentication using SASL and encryption using SSL
• Authentication and encryption using SSL
• Encryption using SSL without client authentication

Enabling security features

To enable security features, in the KafkaSink spec, you can reference a secret:

apiVersion: eventing.knative.dev/v1alpha1
kind: KafkaSink
metadata:
   name: my-kafka-sink
   namespace: default
spec:
   topic: mytopic
   bootstrapServers:
      - my-cluster-kafka-bootstrap.kafka:9092
   auth:
     secret:
       ref:
         name: my_secret

Note

The secret my_secret must exist in the same namespace of the KafkaSink. Certificates and keys must be in PEM format._

Authentication using SASL

Knative supports the following SASL mechanisms:

• PLAIN
• SCRAM-SHA-256
• SCRAM-SHA-512

To use a specific SASL mechanism replace <sasl_mechanism> with the mechanism of your choice.

Authentication using SASL without encryption

kubectl create secret --namespace <namespace> generic <my_secret> \
  --from-literal=protocol=SASL_PLAINTEXT \
  --from-literal=sasl.mechanism=<sasl_mechanism> \
  --from-literal=user=<my_user> \
  --from-literal=password=<my_password>

Authentication using SASL and encryption using SSL

kubectl create secret --namespace <namespace> generic <my_secret> \
  --from-literal=protocol=SASL_SSL \
  --from-literal=sasl.mechanism=<sasl_mechanism> \
  --from-file=ca.crt=caroot.pem \
  --from-literal=user=<my_user> \
  --from-literal=password=<my_password>

Encryption using SSL without client authentication

kubectl create secret --namespace <namespace> generic <my_secret> \
  --from-literal=protocol=SSL \
  --from-file=ca.crt=<my_caroot.pem_file_path> \
  --from-literal=user.skip=true

Authentication and encryption using SSL

kubectl create secret --namespace <namespace> generic <my_secret> \
  --from-literal=protocol=SSL \
  --from-file=ca.crt=<my_caroot.pem_file_path> \
  --from-file=user.crt=<my_cert.pem_file_path> \
  --from-file=user.key=<my_key.pem_file_path>

Note

The ca.crt can be omitted to enable fallback and use the system's root CA set.

Kafka Producer configurations

A Kafka Producer is the component responsible for sending events to the Apache Kafka cluster. You can change the configuration for Kafka Producers in your cluster by modifying the config-kafka-sink-data-plane ConfigMap in the knative-eventing namespace.

Documentation for the settings available in this ConfigMap is available on the Apache Kafka website, in particular, Producer configurations.

Enable debug logging for data plane components

To enable debug logging for data plane components change the logging level to DEBUG in the kafka-config-logging ConfigMap.

1. Create the kafka-config-logging ConfigMap as a YAML file that contains the following:

   apiVersion: v1
   kind: ConfigMap
   metadata:
     name: kafka-config-logging
     namespace: knative-eventing
   data:
     config.xml: |
       <configuration>
         <appender name="jsonConsoleAppender" class="ch.qos.logback.core.ConsoleAppender">
           <encoder class="net.logstash.logback.encoder.LogstashEncoder"/>
         </appender>
         <root level="DEBUG">
           <appender-ref ref="jsonConsoleAppender"/>
         </root>
       </configuration>
   

2. 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.

3. Restart the kafka-sink-receiver:

   kubectl rollout restart deployment -n knative-eventing kafka-sink-receiver