What is the best practise to pass a conf file to a service?

In normal system with docker, this is just a “-v myconf:guest_conf”. But with RancherOS, there are only a few preshared volumes and I cannot see any as a proper place to hold conf files.

So I tried write_files function of cloud_config.yml. But it confused me. First of all, it is doing something. When I made a wrong path, it blocks system booting. Second of all, writing to actual filesystem, or container, did not get me the file.

So what is the best practise here?

PS: I am running RancherOS on RaspberryPi3.