Note on IPs and DNS *mostly AWS

 1. Your Zookeeper & Kafka must know their hostname and/or IP

2. These are not supposed to change over time, even after a reboot, otherwise your setup will be broken.

3. Options:

    - Use an Elastic Public IP == constat public IP

        you will be able to access your cluster from the outside (e.g. laptop)

    - Use a secondary ENI == constant private IP (this course)

        you will not be able to access your cluster from the outside

        you will only be able to access the cluster from within your network

    - Use DNS names (private or public) == no need to keep fixed IP

        public means you can access instances from outside

        private means you can't access instance from outside