Expose the Kafka cluster to external applications

There are two methods to expose your Apache Kafka cluster so that external client applications that run outside the Kubernetes cluster can access it:

using LoadBalancer type services
using NodePort type services

The LoadBalancer method is a convenient way to publish your Kafka cluster, as you don’t have to set up a Load Balancer, provision public IPs, configure routing rules, and so on, since all these are taken care for you. Also, this method has the advantage of reducing your attack surface, since you don’t have to make the Kubernetes cluster’s nodes directly reachable from outside, because incoming external traffic is routed to the nodes of the Kubernetes cluster through the Load Balancer.

The NodePort method provides access to Kafka for external clients through the external public IP of the nodes of the Kubernetes cluster.

This NodePort method is a good fit when:

your Kubernetes distribution or hosting environment does not support Load Balancers,
business requirements make the extra hops introduced by the Load Balancer and Ingress controller unacceptable, or
the environment where the Kubernetes cluster is hosted is locked down, and thus the Kubernetes nodes are not reachable through their public IPs from outside.

External listeners

You can expose the Kafka cluster outside the Kubernetes cluster by declaring one or more externalListeners in the KafkaCluster custom resource. The following externalListeners configuration snippet creates two external access points through which the Kafka cluster’s brokers can be reached. These external listeners are registered in the advertised.listeners Kafka broker configuration as EXTERNAL1://...,EXTERNAL2://....

By default, external listeners use the LoadBalancer access method.

listenersConfig:
  externalListeners:
    - type: "plaintext"
      name: "external1"
      externalStartingPort: 19090
      containerPort: 9094
    - type: "plaintext"
      name: "external2"
      externalStartingPort: 19090
      containerPort: 9095

Expose cluster using a LoadBalancer

To configure an external listener that uses the LoadBalancer access method, complete the following steps.

Edit the KafkaCluster custom resource.
Add an externalListeners section under listenersConfig. The following example creates a Load Balancer for the external listener, external1. Each broker in the cluster receives a dedicated port number on the Load Balancer which is computed as broker port number = externalStartingPort + broker id. This will be registered in each broker’s config as advertised.listeners=EXTERNAL1://<loadbalancer-public-ip>:<broker port number>.
```
listenersConfig:
  externalListeners:
    - type: "plaintext"
      name: "external1"
      externalStartingPort: 19090
      containerPort: 9094
      accessMethod: LoadBalancer
```
Configure an ingress controller in the ingressController field of the KafkaCluster custom resource. For example:
```
spec:
  ingressController: "envoy"
```
The ingress controllers that are currently supported are:
- envoy: uses Envoy Proxy as an ingress controller.
- istioingress: uses Istio Gateway as an ingress controller. This is the default controller for Kafka clusters provisioned with Streaming Data Manager, since those clusters run inside an Istio mesh.
Configure additional parameters for the ingress controller as needed for your environment, for example, number of replicas, resource requirements and resource limits. You can be configure such parameters using the envoyConfig and istioIngressConfig fields, respectively.
(Optional) For external access through a static URL instead of the load balancer’s public IP, specify the URL in the hostnameOverride field of the external listener that resolves to the public IP of the load balancer. The broker address will be advertised as, advertised.listeners=EXTERNAL1://kafka-1.dev.my.domain:<broker port number>.
```
listenersConfig:
  externalListeners:
    - type: "plaintext"
      name: "external1"
      externalStartingPort: 19090
      containerPort: 9094
      accessMethod: LoadBalancer
      hostnameOverride: kafka-1.dev.my.domain
```
Apply the KafkaCluster custom resource to the cluster.

Expose cluster using a NodePort

Using the NodePort access method, external listeners make Kafka brokers accessible through either the external IP of a Kubernetes cluster’s node, or on an external IP that routes into the cluster.

To configure an external listener that uses the NodePort access method, complete the following steps.

Edit the KafkaCluster custom resource.
Add an externalListeners section under listenersConfig. The following example creates a NodePort type service separately for each broker. Brokers can be reached from outside the Kubernetes cluster at <any node public ip>:<broker port number> where the <broker port number> is computed as externalStartingPort + broker id. The externalStartingPort must fall into the range allocated for nodeports on the Kubernetes cluster, which is specified via –service-node-port-range (see the Kubernetes documentation).
```
listenersConfig:
  externalListeners:
    - type: "plaintext"
      name: "external1"
      externalStartingPort: 32000
      containerPort: 9094
      accessMethod: NodePort
```
(Optional) For external access through a dynamic URL, specify a suffix in the hostnameOverride field of the external listener:
```
listenersConfig:
  externalListeners:
    - type: "plaintext"
      name: "external1"
      externalStartingPort: 32000
      containerPort: 9094
      accessMethod: NodePort
      hostnameOverride: .dev.example.com
```
The hostnameOverride behaves differently here than with LoadBalancer access method. In this case, each broker will be advertised as advertised.listeners=EXTERNAL1://<kafka-cluster-name>-<broker-id>.<external listener name>.<namespace><value-specified-in-hostnameOverride-field>:<broker port number>. If a three-broker Kafka cluster named kafka is running in the kafka namespace, the advertised.listeners for the brokers will look like this:
- broker 0:
  - advertised.listeners=EXTERNAL1://kafka-0.external1.kafka.dev.my.domain:32000
- broker 1:
  - advertised.listeners=EXTERNAL1://kafka-1.external1.kafka.dev.my.domain:32001
- broker 2:
  - advertised.listeners=EXTERNAL1://kafka-2.external1.kafka.dev.my.domain:32002
Apply the KafkaCluster custom resource to the cluster.

NodePort external IP

Kafka brokers can be made accessible on external IPs that are not node IP, but can route into the Kubernetes cluster. These external IPs can be set for each broker in the KafkaCluster custom resource as in the following example:

brokers:
- id: 0
  brokerConfig:
    nodePortExternalIP:
        external1: 13.53.214.23 # if "hostnameOverride" is not set for "external1" external listener, then broker is advertised on this IP
- id: 1
    brokerConfig:
    nodePortExternalIP:
        external1: 13.48.71.170 # if "hostnameOverride" is not set for "external1" external listener, then broker is advertised on this IP
- id: 2
    brokerConfig:
    nodePortExternalIP:
        external1: 13.49.70.146 # if "hostnameOverride" is not set for "external1" external listener, then broker is advertised on this IP

If hostnameOverride field is not set, then broker address is advertised as follows:

broker 0:
- advertised.listeners=EXTERNAL1://13.53.214.23:9094
broker 1:
- advertised.listeners=EXTERNAL1://13.48.71.170:9094
broker 2:
- advertised.listeners=EXTERNAL1://13.49.70.146:9094

If both hostnameOverride and nodePortExternalIP fields are set:

broker 0:
- advertised.listeners=EXTERNAL1://kafka-0.external1.kafka.dev.my.domain:9094
broker 1:
- advertised.listeners=EXTERNAL1://kafka-1.external1.kafka.dev.my.domain:9094
broker 2:
- advertised.listeners=EXTERNAL1://kafka-2.external1.kafka.dev.my.domain:9094

Note: If nodePortExternalIP is set, then the containerPort from the external listener config is used as a broker port, and is the same for each broker.

SASL authentication on external listeners

To enable sasl_plaintext authentication on the external listener, modify the externalListeners section of the KafkaCluster CR according to the following example. This will enable an external listener on port 19090.

  listenersConfig:
    externalListeners:
    - config:
        defaultIngressConfig: ingress-sasl
        ingressConfig:
          ingress-sasl:
            istioIngressConfig:
              gatewayConfig:
                credentialName: istio://sds
                mode: SIMPLE
      containerPort: 9094
      externalStartingPort: 19090
      name: external
      type: sasl_plaintext

To connect to this listener using the Kafka 3.1.0 (and above) console producer, complete the following steps:

Set the producer properties like this. Replace the parameters between brackets as needed for your environment:

sasl.mechanism=OAUTHBEARER
security.protocol=SASL_SSL
sasl.login.callback.handler.class=org.apache.kafka.common.security.oauthbearer.secured.OAuthBearerLoginCallbackHandler
sasl.oauthbearer.token.endpoint.url=<https://myidp.example.com/oauth2/default/v1/token>
sasl.jaas.config=org.apache.kafka.common.security.oauthbearer.OAuthBearerLoginModule required \
  clientId="<oauth-client-id>" \
  clientSecret="<client-secret>" \
  scope="kafka:write";
ssl.truststore.location=/ssl/trustore.jks
ssl.truststore.password=truststorepass
ssl.endpoint.identification.algorithm=

Run the following command:

kafka-console-producer.sh --bootstrap-server <your-loadbalancer-ip>:19090 --topic <your-topic-name> --producer.config producer.properties

To consume messages from this listener using the Kafka 3.1.0 (and above) console consumer, complete the following steps:

Set the consumer properties like this. Replace the parameters between brackets as needed for your environment:

group.id=consumer-1
group.instance.id=consumer-1-instance-1
client.id=consumer-1-instance-1
sasl.mechanism=OAUTHBEARER
security.protocol=SASL_SASL
sasl.login.callback.handler.class=org.apache.kafka.common.security.oauthbearer.secured.OAuthBearerLoginCallbackHandler
sasl.oauthbearer.token.endpoint.url=<https://myidp.example.com/oauth2/default/v1/token>
sasl.jaas.config=org.apache.kafka.common.security.oauthbearer.OAuthBearerLoginModule required \
  clientId="<oauth-client-id>" \
  clientSecret="<client-secret>" \
  scope="kafka:read" ;
ssl.endpoint.identification.algorithm=
ssl.truststore.location=/ssl/trustore.jks
ssl.truststore.password=trustorepass

Run the following command:

kafka-console-consumer.sh --bootstrap-server <your-loadbalancer-ip>:19090 --topic <your-topic-name> --consumer.config /opt/kafka/config/consumer.properties --from-beginning