// Module included in the following assemblies:
//
// assembly-configuring-kafka-listeners.adoc

[id='proc-accessing-kafka-using-loadbalancers-{context}']
= Accessing Kafka using loadbalancers

[role="_abstract"]
Use loadbalancers to access a Kafka cluster from an external client outside the Kubernetes cluster.

To connect to a broker, you specify a hostname and port number for the Kafka bootstrap address, as well as the certificate used for TLS encryption.

The procedure shows basic `loadbalancer` listener configuration.
You can use listener properties to enable TLS encryption (`tls`) and specify a client authentication mechanism (`authentication`).
Add additional configuration using `configuration` properties.
For example, you can use the following configuration properties with `loadbalancer` listeners:

`loadBalancerSourceRanges`:: Restricts traffic to a specified list of CIDR (Classless Inter-Domain Routing) ranges.  
`externalTrafficPolicy`:: Specifies whether the service routes external traffic to node-local or cluster-wide endpoints.
`loadBalancerIP`:: Requests a specific IP address when creating a loadbalancer.

For more information on listener configuration, see the link:{BookURLConfiguring}#type-GenericKafkaListener-reference[`GenericKafkaListener` schema reference^].

.Prerequisites

* A running Cluster Operator

In this procedure, the Kafka cluster name is `my-cluster`.
The name of the listener is `external3`.

.Procedure

. Configure a `Kafka` resource with an external listener set to the `loadbalancer` type.
+
For example:
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[source,yaml,subs=attributes+]
----
apiVersion: {KafkaApiVersion}
kind: Kafka
metadata:
  labels:
    app: my-cluster
  name: my-cluster
  namespace: myproject
spec:
  kafka:
    # ...
    listeners:
      - name: external3
        port: 9094
        type: loadbalancer
        tls: true
        authentication:
          type: tls
        # ...
    # ...
----

. Create or update the resource.
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[source,shell,subs=+quotes]
kubectl apply -f _<kafka_configuration_file>_
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A cluster CA certificate to verify the identity of the kafka brokers is also created in the secret `my-cluster-cluster-ca-cert`.
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`loadbalancer` type services and loadbalancers are created for each Kafka broker, as well as an external bootstrap service.
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.Loadbalancer services and loadbalancers created for the bootstraps and brokers
[source,shell]
----
NAME                                  TYPE            CLUSTER-IP      PORT(S)
my-cluster-kafka-external3-0          LoadBalancer    172.30.204.234  9094:30011/TCP
my-cluster-kafka-external3-1          LoadBalancer    172.30.164.89   9094:32544/TCP 
my-cluster-kafka-external3-2          LoadBalancer    172.30.73.151   9094:32504/TCP
my-cluster-kafka-external3-bootstrap  LoadBalancer    172.30.30.228   9094:30371/TCP

NAME                                  EXTERNAL-IP (loadbalancer)
my-cluster-kafka-external3-0          a8a519e464b924000b6c0f0a05e19f0d-1132975133.us-west-2.elb.amazonaws.com
my-cluster-kafka-external3-1          ab6adc22b556343afb0db5ea05d07347-611832211.us-west-2.elb.amazonaws.com 
my-cluster-kafka-external3-2          a9173e8ccb1914778aeb17eca98713c0-777597560.us-west-2.elb.amazonaws.com
my-cluster-kafka-external3-bootstrap  a8d4a6fb363bf447fb6e475fc3040176-36312313.us-west-2.elb.amazonaws.com
----
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The bootstrap address used for client connection is propagated to the `status` of the `Kafka` resource.
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.Example status for the bootstrap address
[source,yaml,subs="+attributes"]
----
status:
  clusterId: Y_RJQDGKRXmNF7fEcWldJQ
  conditions:
    - lastTransitionTime: '2023-01-31T14:59:37.113630Z'
      status: 'True'
      type: Ready
  kafkaVersion: {DefaultKafkaVersion}    
  listeners:
    # ...
    - addresses:
        - host: >-
            a8d4a6fb363bf447fb6e475fc3040176-36312313.us-west-2.elb.amazonaws.com
          port: 9094
      bootstrapServers: >-
        a8d4a6fb363bf447fb6e475fc3040176-36312313.us-west-2.elb.amazonaws.com:9094
      certificates:
        - |
          -----BEGIN CERTIFICATE-----
          
          -----END CERTIFICATE-----
      name: external3
  observedGeneration: 2
  operatorLastSuccessfulVersion: {ProductVersion}
 # ...
----
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The DNS addresses used for client connection are propagated to the `status` of each loadbalancer service.
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.Example status for the bootstrap loadbalancer
[source,yaml]
----
status:
  loadBalancer:
    ingress:
      - hostname: >-
          a8d4a6fb363bf447fb6e475fc3040176-36312313.us-west-2.elb.amazonaws.com
 # ...
----

. Retrieve the bootstrap address you can use to access the Kafka cluster from the status of the `Kafka` resource.
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[source,shell,subs=+quotes]
----
kubectl get kafka my-cluster -o=jsonpath='{.status.listeners[?(@.name=="external3")].bootstrapServers}{"\n"}'

a8d4a6fb363bf447fb6e475fc3040176-36312313.us-west-2.elb.amazonaws.com:9094
----

. Extract the cluster CA certificate.
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[source,shell]
----
kubectl get secret my-cluster-cluster-ca-cert -o jsonpath='{.data.ca\.crt}' | base64 -d > ca.crt
----

. Configure your client to connect to the brokers.

.. Specify the bootstrap host and port in your Kafka client as the bootstrap address to connect to the Kafka cluster. For example, `a8d4a6fb363bf447fb6e475fc3040176-36312313.us-west-2.elb.amazonaws.com:9094`.

.. Add the extracted certificate to the truststore of your Kafka client to configure a TLS connection.
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If you enabled a client authentication mechanism, you will also need to configure it in your client.

NOTE: If you are using your own listener certificates, check whether you need to add the CA certificate to the client's truststore configuration. 
If it is a public (external) CA, you usually won't need to add it.
