Using Knative Kafka - Develop | Serverless | OpenShift Container Platform 4.8

Kafka event delivery and retries
Kafka source
Kafka broker
Creating a Kafka channel by using YAML
Kafka sink
- Using a Kafka sink
Additional resources

Knative Kafka provides integration options for you to use supported versions of the Apache Kafka message streaming platform with OpenShift Serverless. Kafka provides options for event source, channel, broker, and event sink capabilities.

Knative Kafka functionality is available in an OpenShift Serverless installation if a cluster administrator has installed the KnativeKafka custom resource.

Knative Kafka is not currently supported for IBM Z and IBM Power Systems.

Knative Kafka provides additional options, such as:

Kafka source
Kafka channel
Kafka broker (Technology Preview)
Kafka sink (Technology Preview)

Kafka event delivery and retries

Using Kafka components in an event-driven architecture provides "at least once" event delivery. This means that operations are retried until a return code value is received. This makes applications more resilient to lost events; however, it might result in duplicate events being sent.

For the Kafka event source, there is a fixed number of retries for event delivery by default. For Kafka channels, retries are only performed if they are configured in the Kafka channel Delivery spec.

See the Event delivery documentation for more information about delivery guarantees.

Kafka source

You can create a Kafka source that reads events from an Apache Kafka cluster and passes these events to a sink. You can create a Kafka source by using the OpenShift Container Platform web console, the Knative (kn) CLI, or by creating a KafkaSource object directly as a YAML file and using the OpenShift CLI (oc) to apply it.

Creating a Kafka event source by using the web console

After Knative Kafka is installed on your cluster, you can create a Kafka source by using the web console. Using the OpenShift Container Platform web console provides a streamlined and intuitive user interface to create a Kafka source.

Prerequisites

The OpenShift Serverless Operator, Knative Eventing, and the KnativeKafka custom resource are installed on your cluster.
You have logged in to the web console.
You have access to a Red Hat AMQ Streams (Kafka) cluster that produces the Kafka messages you want to import.
You have created a project or have access to a project with the appropriate roles and permissions to create applications and other workloads in OpenShift Container Platform.

Procedure

In the Developer perspective, navigate to the +Add page and select Event Source.
In the Event Sources page, select Kafka Source in the Type section.
Configure the Kafka Source settings:
1. Add a comma-separated list of Bootstrap Servers.
2. Add a comma-separated list of Topics.
3. Add a Consumer Group.
4. Select the Service Account Name for the service account that you created.
5. Select the Sink for the event source. A Sink can be either a Resource, such as a channel, broker, or service, or a URI.
6. Enter a Name for the Kafka event source.
Click Create.

Verification

You can verify that the Kafka event source was created and is connected to the sink by viewing the Topology page.

In the Developer perspective, navigate to Topology.
View the Kafka event source and sink.

Creating a Kafka event source by using the Knative CLI

You can use the kn source kafka create command to create a Kafka source by using the Knative (kn) CLI. Using the Knative CLI to create event sources provides a more streamlined and intuitive user interface than modifying YAML files directly.

Prerequisites

The OpenShift Serverless Operator, Knative Eventing, Knative Serving, and the KnativeKafka custom resource (CR) are installed on your cluster.
You have created a project or have access to a project with the appropriate roles and permissions to create applications and other workloads in OpenShift Container Platform.
You have access to a Red Hat AMQ Streams (Kafka) cluster that produces the Kafka messages you want to import.
You have installed the Knative (kn) CLI.
Optional: You have installed the OpenShift CLI (oc) if you want to use the verification steps in this procedure.

Procedure

To verify that the Kafka event source is working, create a Knative service that dumps incoming events into the service logs:
```
$ kn service create event-display \
    --image quay.io/openshift-knative/knative-eventing-sources-event-display
```
Create a KafkaSource CR:
```
$ kn source kafka create <kafka_source_name> \
    --servers <cluster_kafka_bootstrap>.kafka.svc:9092 \
    --topics <topic_name> --consumergroup my-consumer-group \
    --sink event-display
```
Replace the placeholder values in this command with values for your source name, bootstrap servers, and topics.

The --servers, --topics, and --consumergroup options specify the connection parameters to the Kafka cluster. The --consumergroup option is optional.

Optional: View details about the KafkaSource CR you created:

$ kn source kafka describe <kafka_source_name>

Example output

Name:              example-kafka-source
Namespace:         kafka
Age:               1h
BootstrapServers:  example-cluster-kafka-bootstrap.kafka.svc:9092
Topics:            example-topic
ConsumerGroup:     example-consumer-group

Sink:
  Name:       event-display
  Namespace:  default
  Resource:   Service (serving.knative.dev/v1)

Conditions:
  OK TYPE            AGE REASON
  ++ Ready            1h
  ++ Deployed         1h
  ++ SinkProvided     1h

Verification steps

Trigger the Kafka instance to send a message to the topic:

$ oc -n kafka run kafka-producer \
    -ti --image=quay.io/strimzi/kafka:latest-kafka-2.7.0 --rm=true \
    --restart=Never -- bin/kafka-console-producer.sh \
    --broker-list <cluster_kafka_bootstrap>:9092 --topic my-topic

Enter the message in the prompt. This command assumes that:

The Kafka cluster is installed in the kafka namespace.
The KafkaSource object has been configured to use the my-topic topic.

Verify that the message arrived by viewing the logs:

$ oc logs $(oc get pod -o name | grep 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/example-kafka-source#example-topic
  subject: partition:46#0
  id: partition:46/offset:0
  time: 2021-03-10T11:21:49.4Z
Extensions,
  traceparent: 00-161ff3815727d8755848ec01c866d1cd-7ff3916c44334678-00
Data,
  Hello!

Knative CLI sink flag

When you create an event source by using the Knative (kn) CLI, you can specify a sink where events are sent to from that resource by using the --sink flag. The sink can be any addressable or callable resource that can receive incoming events from other resources.

The following example creates a sink binding that uses a service, http://event-display.svc.cluster.local, as the sink:

Example command using the sink flag

$ kn source binding create bind-heartbeat \
  --namespace sinkbinding-example \
  --subject "Job:batch/v1:app=heartbeat-cron" \
  --sink http://event-display.svc.cluster.local \ (1)
  --ce-override "sink=bound"

1	`svc` in `http://event-display.svc.cluster.local` determines that the sink is a Knative service. Other default sink prefixes include `channel`, and `broker`.

Creating a Kafka event source by using YAML

Creating Knative resources by using YAML files uses a declarative API, which enables you to describe applications declaratively and in a reproducible manner. To create a Kafka source by using YAML, you must create a YAML file that defines a KafkaSource object, then apply it by using the oc apply command.

Prerequisites

The OpenShift Serverless Operator, Knative Eventing, and the KnativeKafka custom resource are installed on your cluster.
You have created a project or have access to a project with the appropriate roles and permissions to create applications and other workloads in OpenShift Container Platform.
You have access to a Red Hat AMQ Streams (Kafka) cluster that produces the Kafka messages you want to import.
Install the OpenShift CLI (oc).

Procedure

Create a KafkaSource object as a YAML file:

apiVersion: sources.knative.dev/v1beta1
kind: KafkaSource
metadata:
  name: <source_name>
spec:
  consumerGroup: <group_name> (1)
  bootstrapServers:
  - <list_of_bootstrap_servers>
  topics:
  - <list_of_topics> (2)
  sink:
  - <list_of_sinks> (3)

1	A consumer group is a group of consumers that use the same group ID, and consume data from a topic.
2	A topic provides a destination for the storage of data. Each topic is split into one or more partitions.
3	A sink specifies where events are sent to from a source.

Only the v1beta1 version of the API for KafkaSource objects on OpenShift Serverless is supported. Do not use the v1alpha1 version of this API, as this version is now deprecated.

Example KafkaSource object

apiVersion: sources.knative.dev/v1beta1
kind: KafkaSource
metadata:
  name: kafka-source
spec:
  consumerGroup: knative-group
  bootstrapServers:
  - my-cluster-kafka-bootstrap.kafka:9092
  topics:
  - knative-demo-topic
  sink:
    ref:
      apiVersion: serving.knative.dev/v1
      kind: Service
      name: event-display

Apply the KafkaSource YAML file:
```
$ oc apply -f <filename>
```

Verification

Verify that the Kafka event source was created by entering the following command:

$ oc get pods

Example output

NAME                                    READY     STATUS    RESTARTS   AGE
kafkasource-kafka-source-5ca0248f-...   1/1       Running   0          13m

Kafka broker

Kafka broker is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling custome