Does FileMaker Server 16 prevent use of the system apache in macOS? I'm running FileMaker Server 16 ("FMS") on macOS High Sierra, without the macOS Server package. I set the FMS web server components up on ports 8080 and 8443 because I wanted to continue running other web services on ports 80 and 443. 

I notice that FMS runs /usr/sbin/httpd (i.e. Apache) under its fmserver user, with configuration at /Library/FileMaker Server/HTTPServer/conf/httpd.conf.

I was trying to configure the system Apache (at /etc/apache2/httpd.conf and using apachectl start), but couldn't get it working at all, even with the default config. apachectl -t said Syntax OK. There were no error messages or logs, and connections to port 80 were refused.

The only relevant thing I could find on the web is a report of the FMS installer refusing to install if Apache is running as part of macOS Server.

I was able to serve on port 80 using nginx installed via brew.

Is the fact that FMS is running apache preventing me from running it under another user?
I know that it's possible to run both the system instance of Apache in addition to the FileMaker Server instance in version 16, provided they run on different ports, so I guess that's a 'No' to your question.

For a better answer, I suggest you post the question at the community forum where FileMaker support staff also chimes in where appropriate. You can also report this as an issue there and get swift support from them.

https://community.filemaker.com

https://community.filemaker.com/community/discussions/report-an-issue