For example, in this project we use nginx + php-fpm to serve some PHP app:
https://github.com/PrivateBin/docker-nginx-fpm-alpine
It uses s6 to handle nginx + php-fpm services, meaning we have to maintain configuration for s6 services (written in execline), nginx webserver configuration files (nginx proprietary format) and php-fpm (INI format).
I've created a fork that replaces that stack with nginx unit:
https://github.com/PrivateBin/docker-unit-alpine
No need for a service manager and both webserver and php configuration are in one file[1]. What is not well documented IMHO is that you don't have to load the config at runtime - if you place the JSON file in the (compile time changeable) /var/lib/unit directory it will be loaded on startup, similar to a traditional /etc config file. But it also will get updated at runtime, if configuration is uploaded on the config socket, making it persist service restarts, hence /var is more appropriate than /etc.
[1] https://github.com/PrivateBin/docker-unit-alpine/blob/master...