Running tomcat app as low privilege user?

Question

I'm totally new to tomcat so I might be missing something stupidly simple.
I'm trying to run drools' kie-workbench 7.5 in tomcat 8. I configured tomcat and the app to work with root but it doesn't work with user tomcat that I gave ownership and 777 privileges to the whole TOMCAT_HOME directory.
I used this ansible recipe to install tomcat after I tried manually with no luck with both.
192.168.50.8:8080 loads tomcat but when I try to access 192.168.50.8:8080/kie-drools-wb-7.5.0.Final-tomcat8 which is the address of the app I get this error page.
I tried to run tomcat with this command: sudo -u tomcat TOMCAT_HOME/bin/startup.sh
I also tried running it with jsvc with these instructions
And running it as a service doesn't work from my manual installation or the Ansible recipe.

Edit:
logs after launching tomcat with jsvc:
catalina.err, catalina.2018-02-11.log, localhost_access_log..2018-02-11.txt, localhost.2018-02-11.log

Answer 1

The logs are showing the following error:

Caused by: java.nio.file.AccessDeniedException: /.index/datasources/write.lock

Check that you have the correct permissions over that directory.

Hope it helps,