Hello and thanks for your response.
As I mentioned, I installed on FreeBSD. With FreeBSD we have 3 options to install - the pkg system (precompiled), the ports system (compiled on host) and the manual system (you do by hand). I installed using the ports (cd /usr/ports/sysutils/logstash8 && make install clean). The control script - /usr/local/etc/rc.d/logstash - was written by the port maintainer. You can see it below:
FreeBSD control script for logstash
I do not see anything in it that would invoke the requirement for Kerberos so I do not think it's the issue, but I am new to all this so I am counting on help from the experts.