I’m a kafka beginner and I am doing a course on it. Was following along and had to create a producer demo file but I keep getting this error:
[kafka-producer-network-thread | producer-1] WARN org.apache.kafka.clients.NetworkClient – [Producer clientId=producer-1] Connection to node -1 (localhost/127.0.0.1:9092) could not be established. Node may not be available.
[kafka-producer-network-thread | producer-1] WARN org.apache.kafka.clients.NetworkClient – [Producer clientId=producer-1] Bootstrap broker localhost:9092 (id: -1 rack: null) disconnected
[kafka-producer-network-thread | producer-1] INFO org.apache.kafka.clients.NetworkClient – [Producer clientId=producer-1] Node -1 disconnected.
Here is my code:

package io.conduktor.demos.kafka;

import org.apache.kafka.clients.producer.KafkaProducer;
import org.apache.kafka.clients.producer.ProducerRecord;
import org.apache.kafka.common.protocol.types.Field;
import org.apache.kafka.common.serialization.StringSerializer;
import org.slf4j.ILoggerFactory;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.Properties;

public class ProducerDemo {

    private static final Logger log = LoggerFactory.getLogger(ProducerDemo.class.getSimpleName());

    public static void main(String[] args) {
        log.info("Hello World!");

        //create Producer Properties
        Properties properties = new Properties();

        //connect to Localhost
        properties.setProperty("bootstrap.servers", "localhost:9092");

        //connect to Conduktor playground
        //properties.setProperty("bootstrap.servers", "cluster.playground.cdkt.io:9092");
        //properties.setProperty("security.protocol", "SASL_SSL");
        //properties.setProperty("sasl.jaas.config", "org.apache.kafka...");
        //properties.setProperty("sasl.mechanism", "PLAIN");

        //set producer properties
        properties.setProperty("key.serializer", StringSerializer.class.getName());
        properties.setProperty("value.serializer", StringSerializer.class.getName());

        //create the Producer
        KafkaProducer<String, String> producer = new KafkaProducer<>(properties);

        //create a producer Record
        ProducerRecord<String, String> producerRecord =
                new ProducerRecord<>("demo_java","hello world");

        //send data
        producer.send(producerRecord);

        //tell the producer to send all data and block until done --synchronous
        producer.flush();

        //flush and close the producer
        producer.close();

    }
}

I have tried changing the hostports, node ID’s, check for firewalls(all inactive), there’s zero security and I can’t wrap my head around fixing it.