For a cluster that is running in production mode with a production license, once security is enabled, transport TLS/SSL must also be enabled. On the other hand, if we are running with a trial license, then transport TLS/SSL is not obligatory.
If we are running with a production license and we attempt to start the cluster with security enabled before we have enabled transport TLS/SSL, we will see the following error message:
Transport SSL must be enabled for setups with production licenses. Please set [xpack.security.transport.ssl.enabled] to [true] or disable security by setting [xpack.security.enabled] to [false]