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Chapter 6. GenericKafkaListener schema reference

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Used in: KafkaClusterSpec

Full list of GenericKafkaListener schema properties

Configures listeners to connect to Kafka brokers within and outside OpenShift.

You configure the listeners in the Kafka resource.

Example Kafka resource showing listener configuration

apiVersion: kafka.strimzi.io/v1beta2
kind: Kafka
metadata:
  name: my-cluster
spec:
  kafka:
    #...
    listeners:
      - name: plain
        port: 9092
        type: internal
        tls: false
      - name: tls
        port: 9093
        type: internal
        tls: true
        authentication:
          type: tls
      - name: external1
        port: 9094
        type: route
        tls: true
      - name: external2
        port: 9095
        type: ingress
        tls: true
        authentication:
          type: tls
        configuration:
          bootstrap:
            host: bootstrap.myingress.com
          brokers:
          - broker: 0
            host: broker-0.myingress.com
          - broker: 1
            host: broker-1.myingress.com
          - broker: 2
            host: broker-2.myingress.com
    #...

6.1. listeners

You configure Kafka broker listeners using the listeners property in the Kafka resource. Listeners are defined as an array.

Example listener configuration

listeners:
  - name: plain
    port: 9092
    type: internal
    tls: false

The name and port must be unique within the Kafka cluster. By specifying a unique name and port for each listener, you can configure multiple listeners. The name can be up to 25 characters long, comprising lower-case letters and numbers.

6.2. port

The port number is the port used in the Kafka cluster, which might not be the same port used for access by a client.

  • loadbalancer listeners use the specified port number, as do internal and cluster-ip listeners
  • ingress and route listeners use port 443 for access
  • nodeport listeners use the port number assigned by OpenShift

For client connection, use the address and port for the bootstrap service of the listener. You can retrieve this from the status of the Kafka resource.

Example command to retrieve the address and port for client connection

oc get kafka <kafka_cluster_name> -o=jsonpath='{.status.listeners[?(@.name=="<listener_name>")].bootstrapServers}{"\n"}'

Important

When configuring listeners for client access to brokers, you can use port 9092 or higher (9093, 9094, and so on), but with a few exceptions. The listeners cannot be configured to use the ports reserved for interbroker communication (9090 and 9091), Prometheus metrics (9404), and JMX (Java Management Extensions) monitoring (9999).

6.3. type

The type is set as internal, or for external listeners, as route, loadbalancer, nodeport, ingress or cluster-ip. You can also configure a cluster-ip listener, a type of internal listener you can use to build custom access mechanisms.

internal

You can configure internal listeners with or without encryption using the tls property.

Example internal listener configuration

#...
spec:
  kafka:
    #...
    listeners:
      #...
      - name: plain
        port: 9092
        type: internal
        tls: false
      - name: tls
        port: 9093
        type: internal
        tls: true
        authentication:
          type: tls
    #...

route

Configures an external listener to expose Kafka using OpenShift Routes and the HAProxy router.

A dedicated Route is created for every Kafka broker pod. An additional Route is created to serve as a Kafka bootstrap address. Kafka clients can use these Routes to connect to Kafka on port 443. The client connects on port 443, the default router port, but traffic is then routed to the port you configure, which is 9094 in this example.

Example route listener configuration

#...
spec:
  kafka:
    #...
    listeners:
      #...
      - name: external1
        port: 9094
        type: route
        tls: true
    #...

ingress

Configures an external listener to expose Kafka using Kubernetes Ingress and the Ingress NGINX Controller for Kubernetes.

A dedicated Ingress resource is created for every Kafka broker pod. An additional Ingress resource is created to serve as a Kafka bootstrap address. Kafka clients can use these Ingress resources to connect to Kafka on port 443. The client connects on port 443, the default controller port, but traffic is then routed to the port you configure, which is 9095 in the following example.

You must specify the hostnames used by the bootstrap and per-broker services using GenericKafkaListenerConfigurationBootstrap and GenericKafkaListenerConfigurationBroker properties.

Example ingress listener configuration

#...
spec:
  kafka:
    #...
    listeners:
      #...
      - name: external2
        port: 9095
        type: ingress
        tls: true
        authentication:
          type: tls
        configuration:
          bootstrap:
            host: bootstrap.myingress.com
          brokers:
          - broker: 0
            host: broker-0.myingress.com
          - broker: 1
            host: broker-1.myingress.com
          - broker: 2
            host: broker-2.myingress.com
  #...

Note

External listeners using Ingress are currently only tested with the Ingress NGINX Controller for Kubernetes.

loadbalancer

Configures an external listener to expose Kafka using a Loadbalancer type Service.

A new loadbalancer service is created for every Kafka broker pod. An additional loadbalancer is created to serve as a Kafka bootstrap address. Loadbalancers listen to the specified port number, which is port 9094 in the following example.

You can use the loadBalancerSourceRanges property to configure source ranges to restrict access to the specified IP addresses.

Example loadbalancer listener configuration

#...
spec:
  kafka:
    #...
    listeners:
      - name: external3
        port: 9094
        type: loadbalancer
        tls: true
        configuration:
          loadBalancerSourceRanges:
            - 10.0.0.0/8
            - 88.208.76.87/32
    #...

nodeport

Configures an external listener to expose Kafka using a NodePort type Service.

Kafka clients connect directly to the nodes of OpenShift. An additional NodePort type of service is created to serve as a Kafka bootstrap address.

When configuring the advertised addresses for the Kafka broker pods, Streams for Apache Kafka uses the address of the node on which the given pod is running. You can use preferredNodePortAddressType property to configure the first address type checked as the node address.

Example nodeport listener configuration

#...
spec:
  kafka:
    #...
    listeners:
      #...
      - name: external4
        port: 9095
        type: nodeport
        tls: false
        configuration:
          preferredNodePortAddressType: InternalDNS
    #...

Note

TLS hostname verification is not currently supported when exposing Kafka clusters using node ports.

cluster-ip

Configures an internal listener to expose Kafka using a per-broker ClusterIP type Service.

The listener does not use a headless service and its DNS names to route traffic to Kafka brokers. You can use this type of listener to expose a Kafka cluster when using the headless service is unsuitable. You might use it with a custom access mechanism, such as one that uses a specific Ingress controller or the OpenShift Gateway API.

A new ClusterIP service is created for each Kafka broker pod. The service is assigned a ClusterIP address to serve as a Kafka bootstrap address with a per-broker port number. For example, you can configure the listener to expose a Kafka cluster over an Nginx Ingress Controller with TCP port configuration.

Example cluster-ip listener configuration

#...
spec:
  kafka:
    #...
    listeners:
      - name: clusterip
        type: cluster-ip
        tls: false
        port: 9096
    #...

6.4. tls

The TLS property is required.

To enable TLS encryption, set the tls property to true. For route and ingress type listeners, TLS encryption must be always enabled.

6.5. authentication

Authentication for the listener can be specified as:

  • mTLS (tls)
  • SCRAM-SHA-512 (scram-sha-512)
  • Token-based OAuth 2.0 (oauth)
  • Custom (custom)

6.6. networkPolicyPeers

Use networkPolicyPeers to configure network policies that restrict access to a listener at the network level. The following example shows a networkPolicyPeers configuration for a plain and a tls listener.

In the following example:

  • Only application pods matching the labels app: kafka-sasl-consumer and app: kafka-sasl-producer can connect to the plain listener. The application pods must be running in the same namespace as the Kafka broker.
  • Only application pods running in namespaces matching the labels project: myproject and project: myproject2 can connect to the tls listener.

The syntax of the networkPolicyPeers property is the same as the from property in NetworkPolicy resources.

Example network policy configuration

listeners:
  #...
  - name: plain
    port: 9092
    type: internal
    tls: true
    authentication:
      type: scram-sha-512
    networkPolicyPeers:
      - podSelector:
          matchLabels:
            app: kafka-sasl-consumer
      - podSelector:
          matchLabels:
            app: kafka-sasl-producer
  - name: tls
    port: 9093
    type: internal
    tls: true
    authentication:
      type: tls
    networkPolicyPeers:
      - namespaceSelector:
          matchLabels:
            project: myproject
      - namespaceSelector:
          matchLabels:
            project: myproject2
# ...

6.7. GenericKafkaListener schema properties

PropertyProperty typeDescription

name

string

Name of the listener. The name will be used to identify the listener and the related OpenShift objects. The name has to be unique within given a Kafka cluster. The name can consist of lowercase characters and numbers and be up to 11 characters long.

port

integer

Port number used by the listener inside Kafka. The port number has to be unique within a given Kafka cluster. Allowed port numbers are 9092 and higher with the exception of ports 9404 and 9999, which are already used for Prometheus and JMX. Depending on the listener type, the port number might not be the same as the port number that connects Kafka clients.

type

string (one of [ingress, internal, route, loadbalancer, cluster-ip, nodeport])

Type of the listener. The supported types are as follows:

  • internal type exposes Kafka internally only within the OpenShift cluster.
  • route type uses OpenShift Routes to expose Kafka.
  • loadbalancer type uses LoadBalancer type services to expose Kafka.
  • nodeport type uses NodePort type services to expose Kafka.
  • ingress type uses OpenShift Nginx Ingress to expose Kafka with TLS passthrough.
  • cluster-ip type uses a per-broker ClusterIP service.

tls

boolean

Enables TLS encryption on the listener. This is a required property.

authentication

KafkaListenerAuthenticationTls, KafkaListenerAuthenticationScramSha512, KafkaListenerAuthenticationOAuth, KafkaListenerAuthenticationCustom

Authentication configuration for this listener.

configuration

GenericKafkaListenerConfiguration

Additional listener configuration.

networkPolicyPeers

NetworkPolicyPeer array

List of peers which should be able to connect to this listener. Peers in this list are combined using a logical OR operation. If this field is empty or missing, all connections will be allowed for this listener. If this field is present and contains at least one item, the listener only allows the traffic which matches at least one item in this list.

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