Connection to node -1 could not be established. Broker may not be available - Kafka & Zookeeper

Encountering the error message "Kafka + Zookeeper: Connection to node -1 could not be established. Broker may not be available" suggests an issue with establishing a connection to the Kafka broker through Zookeeper.

1. Ensure both Kafka and Zookeeper are running and accessible.
2. Verify network configuration to allow connections to Kafka and Zookeeper.

   Check the Kafka server configuration in the server.properties file.

   Change the line:

   #listeners=PLAINTEXT://:9092

   to:

   listeners=PLAINTEXT://localhost:9092

   Additionally, make sure to remove the '#' symbol at the beginning of the line to uncomment it.

   This change specifies that Kafka should listen for incoming connections on the localhost interface at port 9092. The original configuration, with '#listeners=PLAINTEXT://:9092', doesn't specify the hostname, which might lead to connectivity issues. By explicitly setting the hostname to 'localhost', you ensure that Kafka listens for connections on the local machine.

3. Check Kafka and Zookeeper configuration files for correct settings, including advertised.listeners and listeners.
4. Verify the client application's configuration, particularly the bootstrap.servers property.
5. Ensure dependencies and versions of Kafka and Zookeeper libraries are compatible.
6. Implement proper error handling and retry mechanisms to handle transient connection issues.

By meticulously following these steps and rectifying any configuration or dependency issues, you should be able to resolve the error and establish a successful connection between Kafka and Zookeeper.