When you mount a single file into Docker, e.g.: -v /path/to/proxy/my_config.conf:/etc/nginx/conf.d/my_config.conf:ro,Z and wonder why your changes do not appear in the container check your editor to edit the original file and not renaming/replacing the original file.

When you use vim add a modeline to your file for example:
# Required when single files are mounted to container, so that inode does not change.
# vim: backupcopy=yes