Apache Kafka listeners

Charmed Apache Kafka comes with a set of listeners that can be enabled for inter- and intracluster communication.

Internal listeners are used for internal traffic and exchange of information between Apache Kafka brokers, whereas external listeners are used for external clients to be optionally enabled based on the relations created on particular charm endpoints. Each listener is characterised by a specific port, scope and protocol.

In the following table, we summarise the protocols, the port and the relation that each listener is bound to. Note that based on whether a certificates relation is present, one of two mutually exclusive types of listeners can be opened.

Listener name	Driving endpoints	Protocol	Port	Scope
SASL_INTERNAL	cluster	SASL_PLAINTEXT	19092	internal
SASL_INTERNAL	cluster + certificates	SASL_SSL	19093	internal
SASL_EXTERNAL	kafka-client	SASL_PLAINTEXT	9092	external
SASL_EXTERNAL	kafka-client + certificates	SASL_SSL	9093	external
SSL_EXTERNAL	trusted-certificate + certificates	SSL	9094	external
SSL_EXTERNAL	trusted-ca + certificates	SSL	9094	external

Note

Since cluster is a peer relation, the SASL_INTERNAL listener is always enabled.