Kafka 0.9.0.1 Java Consumer stuck in awaitMetadataUpdate()

问题

I'm trying to get a simple Kafka Consumer to work using the Java API v0.9.0.1. The kafka server I'm using is a docker container, also running version 0.9.0.1. Below is the consumer code:

public class Consumer {
    public static void main(String[] args) throws IOException {

        KafkaConsumer<String, String> consumer;
        try (InputStream props = Resources.getResource("consumer.props").openStream()) {
            Properties properties = new Properties();
            properties.load(props);
            consumer = new KafkaConsumer<>(properties);
        }

        consumer.subscribe(Arrays.asList("messages"));
        try {
            while (true) {
                ConsumerRecords<String, String> records = consumer.poll(100);
                for (ConsumerRecord<String, String> record : records)
                    System.out.println("Message received: " + record.value());
            }
        }catch(WakeupException ex){
            System.out.println("Exception caught " + ex.getMessage());
        }finally{
            consumer.close();
            System.out.println("After closing KafkaConsumer");
        }
    }
}

However, when starting the consumer, it calls the poll(100) method above and never returns. Debugging, it looks like it gets stuck running the following method in org.apache.kafka.clients.consumer.internals.ConsumerNetworkClient forever:

public void awaitMetadataUpdate() {
    int version = this.metadata.requestUpdate();

    do {
        this.poll(9223372036854775807L);
    } while(this.metadata.version() == version);

}

(both version and this.metadata.version() always seem to be == 2). Additionally, though it throws no errors, messages from my java producer never seen to make it to the queue. I've verified that using the command line kafka tools, I can both send and receive messages from the queue.

Anyone have any clue what's going on here?

回答1:

In case this helps anyone else with similar issues, the solution for me was to set the following environment variables:

ADVERTISED_HOST=localhost
ADVERTISED_PORT=9092

(of course, the values here may change to suit your installation)

Apparently the command line consumer and producer scripts can manage to find and communicate with the broker correctly without these env variables being set, but the Java API implementations cannot. No errors are thrown either, just an infinite loop on the first poll when it tries to update the metadata.

来源：https://stackoverflow.com/questions/37770024/kafka-0-9-0-1-java-consumer-stuck-in-awaitmetadataupdate