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Knative broker for Apache Kafka - Brokers | Eventing | Red Hat OpenShift Serverless 1.34
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Knative broker implementation for Apache Kafka

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

The Knative 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 Knative 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 broker implementation for Apache Kafka 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.

Creating an Apache Kafka broker when it is not configured as the default broker type

If your OpenShift Serverless deployment is not configured to use Kafka broker as the default broker type, you can use one of the following procedures to create a Kafka-based broker.

Creating an Apache Kafka broker 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 broker by using YAML, you must create a YAML file that defines a Broker 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.

  • 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 installed the OpenShift CLI (oc).

Procedure

  1. Create a Kafka-based broker as a YAML file:

    apiVersion: eventing.knative.dev/v1
kind: Broker
metadata:
  annotations:
    eventing.knative.dev/broker.class: Kafka (1)
  name: example-kafka-broker
spec:
  config:
    apiVersion: v1
    kind: configmap
    name: kafka-broker-config (2)
    namespace: knative-eventing
    1 The broker class. If not specified, brokers use the default class as configured by cluster administrators. To use the Kafka broker, this value must be Kafka.
    2 The default config map for Knative brokers for Apache Kafka. This config map is created when the Kafka broker functionality is enabled on the cluster by a cluster administrator.

  2. Apply the Kafka-based broker YAML file:

    $ oc apply -f <filename>

Creating an Apache Kafka broker that uses an externally managed Kafka topic

If you want to use a Kafka broker without allowing it to create its own internal topic, you can use an externally managed Kafka topic instead. To do this, you must create a Kafka Broker object that uses the kafka.eventing.knative.dev/external.topic annotation.

Prerequisites

  • The OpenShift Serverless Operator, Knative Eventing, and the KnativeKafka custom resource are installed on your OpenShift Container Platform cluster.

  • You have access to a Kafka instance such as Red Hat AMQ Streams, and have created a Kafka topic.

  • 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 installed the OpenShift CLI (oc).

Procedure

  1. Create a Kafka-based broker as a YAML file:

    apiVersion: eventing.knative.dev/v1
kind: Broker
metadata:
  annotations:
    eventing.knative.dev/broker.class: Kafka (1)
    kafka.eventing.knative.dev/external.topic: <topic_name> (2)
...
    1 The broker class. If not specified, brokers use the default class as configured by cluster administrators. To use the Kafka broker, this value must be Kafka.
    2 The name of the Kafka topic that you want to use.

  2. Apply the Kafka-based broker YAML file:

    $ oc apply -f <filename>

Knative Broker implementation for Apache Kafka with isolated data plane

The Knative Broker implementation for Apache Kafka with isolated data plane 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 customers to test functionality and provide feedback during the development process.

For more information about the support scope of Red Hat Technology Preview features, see Technology Preview Features Support Scope.

The Knative Broker implementation for Apache Kafka has 2 planes:

Control plane

Consists of controllers that talk to the Kubernetes API, watch for custom objects, and manage the data plane.

Data plane

The collection of components that listen for incoming events, talk to Apache Kafka, and send events to the event sinks. The Knative Broker implementation for Apache Kafka data plane is where events flow. The implementation consists of kafka-broker-receiver and kafka-broker-dispatcher deployments.

When you configure a Broker class of Kafka, the Knative Broker implementation for Apache Kafka uses a shared data plane. This means that the kafka-broker-receiver and kafka-broker-dispatcher deployments in the knative-eventing namespace are used for all Apache Kafka Brokers in the cluster.

However, when you configure a Broker class of KafkaNamespaced, the Apache Kafka broker controller creates a new data plane for each namespace where a broker exists. This data plane is used by all KafkaNamespaced brokers in that namespace. This provides isolation between the data planes, so that the kafka-broker-receiver and kafka-broker-dispatcher deployments in the user namespace are only used for the broker in that namespace.

As a consequence of having separate data planes, this security feature creates more deployments and uses more resources. Unless you have such isolation requirements, use a regular Broker with a class of Kafka.

Creating a Knative broker for Apache Kafka that uses an isolated data plane

The Knative Broker implementation for Apache Kafka with isolated data plane 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 customers to test functionality and provide feedback during the development process.

For more information about the support scope of Red Hat Technology Preview features, see Technology Preview Features Support Scope.

To create a KafkaNamespaced broker, you must set the eventing.knative.dev/broker.class annotation to KafkaNamespaced.

Prerequisites

  • The OpenShift Serverless Operator, Knative Eventing, and the KnativeKafka custom resource are installed on your OpenShift Container Platform cluster.

  • You have access to an Apache Kafka instance, such as Red Hat AMQ Streams, and have created a Kafka topic.

  • 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 installed the OpenShift CLI (oc).

Procedure

  1. Create an Apache Kafka-based broker by using a YAML file:

    apiVersion: eventing.knative.dev/v1
kind: Broker
metadata:
  annotations:
    eventing.knative.dev/broker.class: KafkaNamespaced (1)
  name: default
  namespace: my-namespace (2)
spec:
  config:
    apiVersion: v1
    kind: configmap
    name: my-config (2)
...
    1 To use the Apache Kafka broker with isolated data planes, the broker class value must be KafkaNamespaced.
    2 The referenced configmap object my-config must be in the same namespace as the Broker object, in this case my-namespace.

  2. Apply the Apache Kafka-based broker YAML file:

    $ oc apply -f <filename>

The configmap object in spec.config must be in the same namespace as the Broker object:

apiVersion: v1
kind: configmap
metadata:
  name: my-config
  namespace: my-namespace
data:
  ...

After the creation of the first Broker object with the KafkaNamespaced class, the kafka-broker-receiver and kafka-broker-dispatcher deployments are created in the namespace. Subsequently, all brokers with the KafkaNamespaced class in the same namespace will use the same data plane. If no brokers with the KafkaNamespaced class exist in the namespace, the data plane in the namespace is deleted.

Configuring Apache Kafka broker settings

You can configure the replication factor, bootstrap servers, and the number of topic partitions for a Kafka broker, by creating a config map and referencing this config map in the Kafka Broker object.

Knative Eventing supports the full set of topic config options that Kafka supports. To set these options, you must add a key to the configmap with the default.topic.config. prefix.

Prerequisites

  • You have cluster or dedicated administrator permissions on OpenShift Container Platform.

  • The OpenShift Serverless Operator, Knative Eventing, and the KnativeKafka custom resource (CR) are installed on your OpenShift Container Platform cluster.

  • You have created a project or have access to a project that has the appropriate roles and permissions to create applications and other workloads in OpenShift Container Platform.

  • You have installed the OpenShift CLI (oc).

Procedure

  1. Modify the kafka-broker-config config map, or create your own config map that contains the following configuration:

    apiVersion: v1
kind: configmap
metadata:
  name: <config_map_name> (1)
  namespace: <namespace> (2)
data:
  default.topic.partitions: <integer> (3)
  default.topic.replication.factor: <integer> (4)
  bootstrap.servers: <list_of_servers> (5)
  default.topic.config.<config_option>: <value> (6)
    1 The config map name.
    2 The namespace where the config map exists.
    3 The number of topic partitions for the Kafka broker. This controls how quickly events can be sent to the broker. A higher number of partitions requires greater compute resources.
    4 The replication factor of topic messages. This prevents against data loss. A higher replication factor requires greater compute resources and more storage.
    5 A comma separated list of bootstrap servers. This can be inside or outside of the OpenShift Container Platform cluster, and is a list of Kafka clusters that the broker receives events from and sends events to.
    6 A topic config option. For more information, see the full set of possible options and values.

    The default.topic.replication.factor value must be less than or equal to the number of Kafka broker instances in your cluster. For example, if you only have one Kafka broker, the default.topic.replication.factor value should not be more than "1".
    Example Kafka broker config map
    apiVersion: v1
kind: configmap
metadata:
  name: kafka-broker-config
  namespace: knative-eventing
data:
  default.topic.partitions: "10"
  default.topic.replication.factor: "3"
  bootstrap.servers: "my-cluster-kafka-bootstrap.kafka:9092"
  default.topic.config.retention.ms: "3600"

  2. Apply the config map:

    $ oc apply -f <config_map_filename>

  3. Specify the config map for the Kafka Broker object:

    Example Broker object
    apiVersion: eventing.knative.dev/v1
kind: Broker
metadata:
  name: <broker_name> (1)
  namespace: <namespace> (2)
  annotations:
    eventing.knative.dev/broker.class: Kafka (3)
spec:
  config:
    apiVersion: v1
    kind: configmap
    name: <config_map_name> (4)
    namespace: <namespace> (5)
...
    1 The broker name.
    2 The namespace where the broker exists.
    3 The broker class annotation. In this example, the broker is a Kafka broker that uses the class value Kafka.
    4 The config map name.
    5 The namespace where the config map exists.

  4. Apply the broker:

    $ oc apply -f <broker_filename>

Security configuration for the Knative broker implementation for Apache Kafka

Kafka clusters are generally secured by using the TLS or SASL authentication methods. You can configure a Kafka broker or channel to work against a protected Red Hat AMQ Streams cluster by using TLS or SASL.

Red Hat recommends that you enable both SASL and TLS together.

Configuring TLS authentication for Apache Kafka brokers

Transport Layer Security (TLS) is used by Apache Kafka clients and servers to encrypt traffic between Knative and Kafka, as well as for authentication. TLS is the only supported method of traffic encryption for the Knative broker implementation for Apache Kafka.

Prerequisites

  • You have cluster or dedicated administrator permissions on OpenShift Container Platform.

  • The OpenShift Serverless Operator, Knative Eventing, and the KnativeKafka CR are installed on your OpenShift Container Platform 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 a Kafka cluster CA certificate stored as a .pem file.

  • You have a Kafka cluster client certificate and a key stored as .pem files.

  • Install the OpenShift CLI (oc).

Procedure

  1. Create the certificate files as a secret in the knative-eventing namespace:

    $ oc create secret -n knative-eventing generic <secret_name> \
  --from-literal=protocol=SSL \
  --from-file=ca.crt=caroot.pem \
  --from-file=user.crt=certificate.pem \
  --from-file=user.key=key.pem

    Use the key names ca.crt, user.crt, and user.key. Do not change them.

  2. Edit the KnativeKafka CR and add a reference to your secret in the broker spec:

    apiVersion: operator.serverless.openshift.io/v1alpha1
kind: KnativeKafka
metadata:
  namespace: knative-eventing
  name: knative-kafka
spec:
  broker:
    enabled: true
    defaultConfig:
      authSecretName: <secret_name>
...

Configuring SASL authentication for Apache Kafka brokers

Simple Authentication and Security Layer (SASL) is used by Apache Kafka for authentication. If you use SASL authentication on your cluster, users must provide credentials to Knative for communicating with the Kafka cluster; otherwise events cannot be produced or consumed.

Prerequisites

  • You have cluster or dedicated administrator permissions on OpenShift Container Platform.

  • The OpenShift Serverless Operator, Knative Eventing, and the KnativeKafka CR are installed on your OpenShift Container Platform 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 a username and password for a Kafka cluster.

  • You have chosen the SASL mechanism to use, for example, PLAIN, SCRAM-SHA-256, or SCRAM-SHA-512.

  • If TLS is enabled, you also need the ca.crt certificate file for the Kafka cluster.

  • Install the OpenShift CLI (oc).

Procedure

  1. Create the certificate files as a secret in the knative-eventing namespace:

    $ oc create secret -n knative-eventing generic <secret_name> \
  --from-literal=protocol=SASL_SSL \
  --from-literal=sasl.mechanism=<sasl_mechanism> \
  --from-file=ca.crt=caroot.pem \
  --from-literal=password="SecretPassword" \
  --from-literal=user="my-sasl-user"

    • Use the key names ca.crt, password, and sasl.mechanism. Do not change them.

    • If you want to use SASL with public CA certificates, you must use the tls.enabled=true flag, rather than the ca.crt argument, when creating the secret. For example:

      $ oc create secret -n <namespace> generic <kafka_auth_secret> \
  --from-literal=tls.enabled=true \
  --from-literal=password="SecretPassword" \
  --from-literal=saslType="SCRAM-SHA-512" \
  --from-literal=user="my-sasl-user"

  2. Edit the KnativeKafka CR and add a reference to your secret in the broker spec:

    apiVersion: operator.serverless.openshift.io/v1alpha1
kind: KnativeKafka
metadata:
  namespace: knative-eventing
  name: knative-kafka
spec:
  broker:
    enabled: true
    defaultConfig:
      authSecretName: <secret_name>
...

Additional resources