Listener configuration options

Per-listener Kafka configuration

Some Kafka options can be configured per listener rather than only at the broker level using spec.kafka.config. This enables more granular control. For example, you can enforce connection limits or session re-authentication on a specific external listener without affecting internal listeners.

Depending on the option, per-listener configuration uses one of the following mechanisms:

Dedicated fields in the listener configuration

The following options are typed fields in the configuration section of each listener:

• maxConnections – Maximum number of connections allowed for this listener at any time. New connections are blocked if the limit is reached.
• maxConnectionCreationRate – Maximum connection creation rate for this listener. New connections are throttled if the limit is reached.

#...
kind: Kafka
spec:
  kafka:
    listeners:
      - name: external
        port: 9094
        type: loadbalancer
        tls: true
        configuration:
          maxConnections: 1000
          maxConnectionCreationRate: 100

Listener-prefixed properties in spec.kafka.config

The following options can be scoped to a specific listener by adding the listener.name.[***LISTENER NAME***]-[***PORT***]. prefix in spec.kafka.config. The listener name and port in the prefix must match the name and port values of the listener in your Kafka resource, joined with a hyphen:

• connections.max.reauth.ms
• max.connections
• max.connections.per.ip
• max.connections.per.ip.overrides
• max.connection.creation.rate

#...
kind: Kafka
spec:
  kafka:
    config:
      listener.name.external-9094.connections.max.reauth.ms: 3600000
      listener.name.external-9094.max.connections.per.ip: 500

In this example, the listener is named external and runs on port 9094, so the prefix is listener.name.external-9094..

Advertised port template

The advertisedPortTemplate field in the listener configuration controls how Strimzi generates the advertised ports for individual brokers. This is useful for external listener types such as nodeport and loadbalancer, where clients connect directly to specific brokers and need predictable per-broker port numbers.

The template supports a simple mathematical expression using the {nodeId} placeholder and the +, -, and * operators. Strimzi substitutes the broker node ID into the expression to calculate the advertised port for each broker. You can also specify a fixed port number to use the same port for all brokers.

#...
kind: Kafka
spec:
  kafka:
    listeners:
      - name: external
        port: 9094
        type: nodeport
        tls: true
        configuration:
          advertisedPortTemplate: 9000 + {nodeId}

In this example, brokers are advertised on ports 9000, 9001, 9002, and so on, based on their node ID.