Listener configuration is not valid

[haroon9]

While increasing the replica size from 1 to 3 I faced the following issue:
ERROR ListenersValidator:47 - Reconciliation #16864(timer) Kafka(kafka/kafka): Listener configuration is not valid: [listener ingress is missing a broker host name for broker with ID 4 which is required for Ingress based listeners, listener ingress is missing a broker host name for broker with ID 5 which is required for Ingress based listeners]

This happens when I set the broker IDs like this:

  brokers:
    - broker: 0
      host: broker.0.dev.gridcert.ai
      annotations:
        kubernetes.io/ingress.class: nginx
    - broker: 1
      host: broker.1.dev.gridcert.ai
      annotations:
        kubernetes.io/ingress.class: nginx
    - broker: 2
      host: broker.2.dev.gridcert.ai
      annotations:
        kubernetes.io/ingress.class: nginx

But when I changed the IDs to 4 and 5 works fine.

  brokers:
    - broker: 0
      host: broker.0.dev.gridcert.ai
      annotations:
        kubernetes.io/ingress.class: nginx
    - broker: 4
      host: broker.1.dev.gridcert.ai
      annotations:
        kubernetes.io/ingress.class: nginx
    - broker: 5
      host: broker.2.dev.gridcert.ai
      annotations:
        kubernetes.io/ingress.class: nginx

Is there any misconfiguration on my part? As in the cluster, I do not have other brokers running with IDs 1 and 2.

[scholzj]

From the information you shared, it is hard to understand what the exact configuration and state of your cluster looks like. In any case, if you use Ingress type listener, you need to provide a hostname for every single broker node you have. So if you scaled up your cluster to 3 nodes and have brokers with IDs 1, 4 and 5, you would need to configure the hostnames for them otherwise you will get the error you shared above.

But unless you share more information (e.g. full set of used custom resources), it is hard to say for sure why you don't have nodes 1, 2 and 3 -> maybe you use KRaft and those are the controller node IDs?

[haroon9]

@scholzj thanks for the answer. You are correct, we recently migrated to KRaft mode. The controller nodes have the ID 1,2,3 while the Kafka nodes have 0,4,5. Is this by design with KRaft mode?

[scholzj]

In KRaft, the controller nodes and broker nodes share the same ID space. So yes, the node IDs can be mixed like this. What exactly the IDs will be depends on how you added the nodes etc. You can also use annotations to control which node pools is getting which node IDs etc.