Spring Kafka from laptop to dockerized Kafka: Error connecting to node kafka0:9092 (id: 1 rack: null)

Question

Small question regarding connecting a Spring Kafka application to a Dockerized Kafka please.

The code of the Dockerfile is:

version: "3.9"

services:

  kafka:
    networks: [ "mynetwork" ]
    container_name: kafka.mynetwork
    hostname: kafka0
    image: hexhex/kafka-kraft:0.0.10
    environment:
      ADVERTISED_LISTENERS: kafka0:9092
    ports:
      - 9092:9092

  kafka-ui:
    networks: [ "mynetwork" ]
    container_name: kafka-ui.mynetwork
    hostname: kafka-ui.mynetwork
    image: provectuslabs/kafka-ui
    ports:
      - 8080:8080
    environment:
      - KAFKA_CLUSTERS_0_NAME=local
      - KAFKA_CLUSTERS_0_BOOTSTRAPSERVERS=kafka0:9092
    depends_on:
      - kafka

networks:
  mynetwork:
      name: mynetwork

I strongly believe the docker compose file, with its two services, are correct.

I am able to connect to http://localhost:8080 and see the Kafka-UI. I can create topics, etc.

I am able to use the consumer shell inside the kafka container to send and consume message.

Now, I am having a Spring Kafka app, very straightforward, following an online tutorial:

https://www.baeldung.com/spring-kafka

with the code:

@EnableKafka
@Configuration
public class KafkaConsumerConfig {

    @Bean
    public ConsumerFactory<String, Greeting> greetingConsumerFactory() {
        Map<String, Object> props = new HashMap<>();
        props.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
        props.put(ConsumerConfig.GROUP_ID_CONFIG, "greeting");
        props.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest");
        return new DefaultKafkaConsumerFactory<>(props, new StringDeserializer(), new JsonDeserializer<>(Greeting.class));
    }

    @Bean
    public ConcurrentKafkaListenerContainerFactory<String, Greeting> greetingKafkaListenerContainerFactory() {
        ConcurrentKafkaListenerContainerFactory<String, Greeting> factory = new ConcurrentKafkaListenerContainerFactory<>();
        factory.setConsumerFactory(greetingConsumerFactory());
        return factory;
    }

}

@Configuration
public class KafkaProducerConfig {

    @Bean
    public ProducerFactory<String, Greeting> greetingProducerFactory() {
        final Map<String, Object> configProps = Map.of(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092", ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, StringSerializer.class, ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, JsonSerializer.class);
        return new DefaultKafkaProducerFactory<>(configProps);
    }

    @Bean
    public KafkaTemplate<String, Greeting> greetingKafkaTemplate() {
        return new KafkaTemplate<>(greetingProducerFactory());
    }

}

@Service
public class KafkaConsumerService {

    @KafkaListener(topics = "greetingTopicName", groupId = "groupId")
    public void greetingListener(Greeting greeting) {
        System.out.println("greeting " + greeting);
    }

}

@Service
public class KafKaProducerService {
    private static final Logger logger = LoggerFactory.getLogger(KafKaProducerService.class);

    @Autowired
    private KafkaTemplate<String, Greeting> kafkaTemplate;

    public void sendGreetingMessage(Greeting greeting) {
        logger.info(String.format("Message sending -> %s", greeting));
        kafkaTemplate.send("greetingTopicName", greeting);
        logger.info(String.format("Message sent -> %s", greeting));
    }

}

For the bootstrap server, I tried localhost:9092, http://localhost:9092, 0.0.0.0:9092, 127.0.0.1:9092, kafka0:9092 and unfortunately, all yields:

WARN 21172 --- [ntainer#0-0-C-1] org.apache.kafka.clients.NetworkClient   : [Consumer clientId=consumer-groupId-1, groupId=groupId] Error connecting to node kafka0:9092 (id: 2147483646 rack: null)

java.net.UnknownHostException: No such host is known (kafka0)

I am on windows using the latest docker.

Here is the complete trace:

INFO 21172 --- [           main] o.a.k.clients.consumer.ConsumerConfig    : ConsumerConfig values: 
    allow.auto.create.topics = true
    auto.commit.interval.ms = 5000
    auto.offset.reset = latest
    bootstrap.servers = [localhost:9092]

WARN 21172 --- [ntainer#0-0-C-1] org.apache.kafka.clients.NetworkClient   : [Consumer clientId=consumer-groupId-1, groupId=groupId] Error connecting to node kafka0:9092 (id: 2147483646 rack: null)

java.net.UnknownHostException: No such host is known (kafka0)
    at java.base/java.net.Inet6AddressImpl.lookupAllHostAddr(Native Method) ~[na:na]
    at java.base/java.net.InetAddress$PlatformNameService.lookupAllHostAddr(InetAddress.java:933) ~[na:na]
    at java.base/java.net.InetAddress.getAddressesFromNameService(InetAddress.java:1529) ~[na:na]
    at java.base/java.net.InetAddress$NameServiceAddresses.get(InetAddress.java:852) ~[na:na]
    at java.base/java.net.InetAddress.getAllByName0(InetAddress.java:1519) ~[na:na]
    at java.base/java.net.InetAddress.getAllByName(InetAddress.java:1377) ~[na:na]
    at java.base/java.net.InetAddress.getAllByName(InetAddress.java:1305) ~[na:na]
    at org.apache.kafka.clients.DefaultHostResolver.resolve(DefaultHostResolver.java:27) ~[kafka-clients-3.3.1.jar:na]
    at org.apache.kafka.clients.ClientUtils.resolve(ClientUtils.java:110) ~[kafka-clients-3.3.1.jar:na]
    at org.apache.kafka.clients.ClusterConnectionStates$NodeConnectionState.currentAddress(ClusterConnectionStates.java:510) ~[kafka-clients-3.3.1.jar:na]
    at org.apache.kafka.clients.ClusterConnectionStates$NodeConnectionState.access$200(ClusterConnectionStates.java:467) ~[kafka-clients-3.3.1.jar:na]
    at org.apache.kafka.clients.ClusterConnectionStates.currentAddress(ClusterConnectionStates.java:173) ~[kafka-clients-3.3.1.jar:na]
    at org.apache.kafka.clients.NetworkClient.initiateConnect(NetworkClient.java:990) ~[kafka-clients-3.3.1.jar:na]
    at org.apache.kafka.clients.NetworkClient.ready(NetworkClient.java:301) ~[kafka-clients-3.3.1.jar:na]
    at org.apache.kafka.clients.consumer.internals.ConsumerNetworkClient.tryConnect(ConsumerNetworkClient.java:590) ~[kafka-clients-3.3.1.jar:na]
    at org.apache.kafka.clients.consumer.internals.AbstractCoordinator$FindCoordinatorResponseHandler.onSuccess(AbstractCoordinator.java:901) ~[kafka-clients-3.3.1.jar:na]
    at org.apache.kafka.clients.consumer.internals.AbstractCoordinator$FindCoordinatorResponseHandler.onSuccess(AbstractCoordinator.java:877) ~[kafka-clients-3.3.1.jar:na]
    at org.apache.kafka.clients.consumer.internals.RequestFuture$1.onSuccess(RequestFuture.java:206) ~[kafka-clients-3.3.1.jar:na]
    at org.apache.kafka.clients.consumer.internals.RequestFuture.fireSuccess(RequestFuture.java:169) ~[kafka-clients-3.3.1.jar:na]
    at org.apache.kafka.clients.consumer.internals.RequestFuture.complete(RequestFuture.java:129) ~[kafka-clients-3.3.1.jar:na]
    at org.apache.kafka.clients.consumer.internals.ConsumerNetworkClient$RequestFutureCompletionHandler.fireCompletion(ConsumerNetworkClient.java:617) ~[kafka-clients-3.3.1.jar:na]
    at org.apache.kafka.clients.consumer.internals.ConsumerNetworkClient.firePendingCompletedRequests(ConsumerNetworkClient.java:427) ~[kafka-clients-3.3.1.jar:na]
    at org.apache.kafka.clients.consumer.internals.ConsumerNetworkClient.poll(ConsumerNetworkClient.java:312) ~[kafka-clients-3.3.1.jar:na]
    at org.apache.kafka.clients.consumer.internals.ConsumerNetworkClient.poll(ConsumerNetworkClient.java:230) ~[kafka-clients-3.3.1.jar:na]
    at org.apache.kafka.clients.consumer.internals.AbstractCoordinator.ensureCoordinatorReady(AbstractCoordinator.java:265) ~[kafka-clients-3.3.1.jar:na]
    at org.apache.kafka.clients.consumer.internals.AbstractCoordinator.ensureCoordinatorReady(AbstractCoordinator.java:240) ~[kafka-clients-3.3.1.jar:na]
    at org.apache.kafka.clients.consumer.internals.ConsumerCoordinator.coordinatorUnknownAndUnreadySync(ConsumerCoordinator.java:492) ~[kafka-clients-3.3.1.jar:na]
    at org.apache.kafka.clients.consumer.internals.ConsumerCoordinator.poll(ConsumerCoordinator.java:524) ~[kafka-clients-3.3.1.jar:na]
    at org.apache.kafka.clients.consumer.KafkaConsumer.updateAssignmentMetadataIfNeeded(KafkaConsumer.java:1276) ~[kafka-clients-3.3.1.jar:na]
    at org.apache.kafka.clients.consumer.KafkaConsumer.poll(KafkaConsumer.java:1240) ~[kafka-clients-3.3.1.jar:na]
    at org.apache.kafka.clients.consumer.KafkaConsumer.poll(KafkaConsumer.java:1220) ~[kafka-clients-3.3.1.jar:na]
    at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.pollConsumer(KafkaMessageListenerContainer.java:1665) ~[spring-kafka-3.0.0.jar:3.0.0]
    at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.doPoll(KafkaMessageListenerContainer.java:1640) ~[spring-kafka-3.0.0.jar:3.0.0]
    at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.pollAndInvoke(KafkaMessageListenerContainer.java:1441) ~[spring-kafka-3.0.0.jar:3.0.0]
    at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.run(KafkaMessageListenerContainer.java:1338) ~[spring-kafka-3.0.0.jar:3.0.0]
    at java.base/java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1804) ~[na:na]
    at java.base/java.lang.Thread.run(Thread.java:833) ~[na:na]

INFO 21172 --- [ntainer#0-0-C-1] o.a.k.c.c.internals.ConsumerCoordinator  : [Consumer clientId=consumer-groupId-1, groupId=groupId] (Re-)joining group
WARN 21172 --- [ntainer#0-0-C-1] org.apache.kafka.clients.NetworkClient   : [Consumer clientId=consumer-groupId-1, groupId=groupId] Error connecting to node kafka0:9092 (id: 2147483646 rack: null)

java.net.UnknownHostException: kafka0

To avoi confusions: It is a Spring Kafka app (not inside docker) running from laptop, trying to connect to kafka inside docker.

It is not a dockerized spring app trying to connect to a dockerized kafka, it is not a metal spring kafka app trying to connect to a metal kafka.

Thank you