This interface layer handles the communication between Kafka and its clients. The provider part of this interface provides the Kafka service. The consumer part requires the existence of a provider to function.

Charms providing the Apache Kafka service provide this interface. This interface layer will set the following states, as appropriate:

• {relation_name}.joined The provider has been related to a client, though the client service may not be available yet. At this point, the provider should broadcast Kafka configuration details using:

  • send_port(self, port)
  • send_zookeepers(self, zk_host_port_pair_list)

• {relation_name}.ready Kafka configuration details have been sent. The provider and client should now be able to communicate.

Kafka provider example:

@when('client.joined', 'zookeeper.ready')
def serve_client(client, zookeeper):
    client.send_port(get_kafka_port())
    client.send_zookeepers(zookeeper.zookeepers())

Clients require this interface to connect to Apache Kafka. This interface layer will set the following states, as appropriate:

• {relation_name}.joined The client charm has been related to a Kafka provider. At this point, the charm waits for Kafka configuration details.

• {relation_name}.ready Kafka is now ready for clients. The client charm should get Kafka configuration details using:

  • kafkas()
  • zookeepers()

Kafka client example:

@when('kafka.joined')
@when_not('kafka.ready')
def wait_for_kafka(kafka):
    hookenv.status_set('waiting', 'Waiting for Kafka to become ready')


@when('kafka.ready')
@when_not('myservice.configured')
def configure(kafka):
    for kafka_unit in kafka.kafkas():
        add_kafka(kafka_unit['host'], kafka_unit['port'])
    set_state('myservice.configured')

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