apache2nginx is a command line tool, which can be used to generate nginx config file according to given config files of Apache.
The website / repo is at https://github.com/nhnc-nginx/apache2nginx
I have used this for migration and found it very useful.
Created attachment 422076 [details]
A working, but very simple ebuild that very likely can use improvement.
This seems to be quite old, last commit in 2012.