I am a novice with respect to anything networking.
In the [[https://www.redmine.org/projects/redmine/wiki/HowTo_Install_Redmine_on_Ubuntu_step_by_step]] in the section on configuring Apache your are instructed to modify /etc/apache2/mods-available/passenger.conf with
<IfModule mod_passenger.c> PassengerDefaultUser www-data PassengerRoot /usr PassengerRuby /usr/bin/ruby </IfModule>
I found that listing passenger root as /usr caused localhost/redmine to give the index.
changing to usr/lib/ruby/vendor_ruby/phusion_passenger/locations resulted in expected behavior.