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Using Knative Kafka - Develop | Serverless | OpenShift Container Platform 4.6
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Using Knative Kafka

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

  • Kafka sink

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

  1. In the Developer perspective, navigate to the Add page and select Event Source.

  2. In the Event Sources page, select Kafka Source in the Type section.

  3. 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.

  4. Click Create.

Verification

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

  1. In the Developer perspective, navigate to Topology.

  2. View the Kafka event source and sink.

    View the Kafka source and service in the Topology view

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

  1. 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

  2. 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.

  3. 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

  1. 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.

  2. 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

  1. 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

  2. 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

For production-ready Knative Eventing deployments, Red Hat recommends using the Knative Kafka broker implementation. The Kafka broker is an Apache Kafka native implementation of the Knative broker, which sends CloudEvents directly to the Kafka instance.

The Federal Information Processing Standards (FIPS) mode is disabled for Kafka broker.

The Kafka broker has a native integration with Kafka for storing and routing events. This allows better integration with Kafka for the broker and trigger model over other broker types, and reduces network hops. Other benefits of the Kafka broker implementation include:

  • At-least-once delivery guarantees

  • Ordered delivery of events, based on the CloudEvents partitioning extension

  • Control plane high availability

  • A horizontally scalable data plane

The Knative Kafka broker stores incoming CloudEvents as Kafka records, using the binary content mode. This means that all CloudEvent attributes and extensions are mapped as headers on the Kafka record, while the data spec of the CloudEvent corresponds to the value of the Kafka record.

For information about using Kafka brokers, see Creating brokers.

Creating a Kafka channel by using YAML

Creating Knative resources by using YAML files uses a declarative API, which enables you to describe channels declaratively and in a reproducible manner. You can create a Knative Eventing channel that is backed by Kafka topics by creating a Kafka channel. To create a Kafka channel by using YAML, you must create a YAML file that defines a KafkaChannel 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 OpenShift Container Platform cluster.

  • Install the OpenShift CLI (oc).

  • 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

  1. Create a KafkaChannel object as a YAML file:

    apiVersion: messaging.knative.dev/v1beta1
kind: KafkaChannel
metadata:
  name: example-channel
  namespace: default
spec:
  numPartitions: 3
  replicationFactor: 1

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

  2. Apply the KafkaChannel YAML file:

    $ oc apply -f <filename>

Kafka sink

Kafka sinks are a type of event sink that are available if a cluster administrator has enabled Kafka on your cluster. You can send events directly from an event source to a Kafka topic by using a Kafka sink.

Using a Kafka sink

You can create an event sink called a Kafka sink that sends events to a Kafka topic. 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 sink by using YAML, you must create a YAML file that defines a KafkaSink object, then apply it by using the oc apply command.

Prerequisites

  • The OpenShift Serverless Operator, Knative Eventing, 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.

  • Install the OpenShift CLI (oc).

Procedure

  1. Create a KafkaSink object definition as a YAML file:

    Kafka sink YAML
    apiVersion: eventing.knative.dev/v1alpha1
kind: KafkaSink
metadata:
  name: <sink-name>
  namespace: <namespace>
spec:
  topic: <topic-name>
  bootstrapServers:
   - <bootstrap-server>

  2. To create the Kafka sink, apply the KafkaSink YAML file:

    $ oc apply -f <filename>

  3. Configure an event source so that the sink is specified in its spec:

    Example of a Kafka sink connected to an API server source
    apiVersion: sources.knative.dev/v1alpha2
kind: ApiServerSource
metadata:
  name: <source-name> (1)
  namespace: <namespace> (2)
spec:
  serviceAccountName: <service-account-name> (3)
  mode: Resource
  resources:
  - apiVersion: v1
    kind: Event
  sink:
    ref:
      apiVersion: eventing.knative.dev/v1alpha1
      kind: KafkaSink
      name: <sink-name> (4)
    1 The name of the event source.
    2 The namespace of the event source.
    3 The service account for the event source.
    4 The Kafka sink name.

Additional resources